Refrigerant, Oil & Coolant System Sealing
H-O Products die-cuts and converts the wet-side gasket set on HVAC and refrigeration equipment: compressor flange gaskets, service-valve and fitting seals, oil-exposed gaskets for POE and PAG lubricants, chilled-water and glycol-loop gaskets, condensate-pan seals, and the elastomer set behind the move to low-GWP refrigerants, built to your drawing. Refrigerant and oil compatibility is reviewed against the vendor TDS compatibility tables, not assumed from a family name.
Built for: reciprocating, scroll, and screw compressors; air-cooled and water-cooled chillers; condensing units and refrigeration racks; hydronic and glycol loops; and the A2L-adjacent material reviews driving the low-GWP transition, with elastomer classes referenced per ASTM D2000 and fluid-immersion behavior per ASTM D471 on the grade TDSs.
To seal a refrigerant, oil, and coolant system, pick the elastomer from the fluid pair, not the part name. Compressor flange gaskets that see refrigerant and refrigerant oil together commonly specify HNBR by durometer or neoprene (CR) by designation, with compatibility read from the vendor TDS compatibility tables. Service-valve and fitting seals take HNBR or FKM/Viton® where the fluid runs hot or aggressive.
POE and PAG oil-exposed gaskets need a grade whose TDS immersion data covers the synthetic lubricant, because oils tuned for one chemistry can attack a compound suited to another. Chilled-water and glycol-loop gaskets specify EPDM by designation, the family at home in water and glycol and deliberately kept out of the oil zones. Condensate-pan seals take EPDM or cork-nitrile cut to the pan profile.
And the low-GWP refrigerant transition is a review, not a single answer: A2L-adjacent material selection is done by designation against the vendor TDS compatibility tables for the named refrigerant and oil. Elastomer classes are referenced per ASTM D2000; fluid-immersion behavior per ASTM D471; refrigerant safety classes (incl. A2L) per ASHRAE 34.
Compatibility is per vendor TDS compatibility tables; final material selection should be validated in the application. See the quote form for ordering details.
Material-level, per the vendor TDS: ASTM D2000 (rubber line-call classification for HNBR, neoprene, FKM, EPDM) · ASTM D471 (rubber property, effect of liquids: the fluid-immersion method behind every compatibility statement here) · ASTM D1056 (flexible cellular rubber classes for sponge and foam seals) · UL 94 (flame classes, incl. V-0, on the rated grades). Referenced by designation as system or fluid context: ASHRAE 34 (refrigerant designation and safety classification, including the A2L lower-flammability class).
Refrigerant and oil compatibility is read from the vendor TDS compatibility tables for the named fluid pair, not claimed as a blanket family property.
- Compressor flange, refrigerant + oil: HNBR by durometer / neoprene
- Hot or aggressive fitting seals: FKM/Viton® by designation
- POE/PAG oil-exposed gaskets: grade per the oil's TDS immersion data
- Chilled-water / glycol loops: EPDM by designation
- Condensate-pan seals: EPDM sponge / cork-nitrile
- Low-GWP / A2L-adjacent review: by designation, per vendor TDS
- Conformable seal in aggressive fluid: Viton® sponge 1628
- Near-universal chemistry, extreme duty: FFKM
Where are you in the spec process?
This page serves engineers who already know the gasket they want and engineers still matching an elastomer to a refrigerant-and-oil pair. Pick the path that matches where you are; you don't have to read the rest.
Send a drawing, get a quote
A compressor flange gasket, a service-valve seal, an oil-exposed gasket, a glycol-loop gasket, a condensate-pan seal, or a complete die-cut per-unit wet-side gasket kit on your drawing.
Skip to the quote form →Walk the six sealing jobs one fluid at a time
Six numbered jobs (compressor, valves, oil, glycol, condensate, low-GWP transition), a refrigerant-duty checklist builder, a fluid-vs-family comparison matrix, and six material families with TDS-cited methods and by-designation standards language.
Start with job 1 →
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1Send drawingUpload a DXF, STEP, or PDF, or describe the flange, valve, or pan joint. Name the refrigerant and the oil. A sample part works too.
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2Compatibility reviewEngineering reviews the refrigerant-and-oil pair, temperature, and pressure against the vendor TDS compatibility tables and ASTM D471 immersion data, checks flange loading and compressibility, and frames the standards language correctly: elastomer classes per ASTM D2000 on the TDS, refrigerant safety classes (ASHRAE 34, incl. A2L) by designation.
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3PrototypeSamples typically ship in 3–5 business days for common die-cut configurations on materials we keep on hand. Made-to-order; MOQ varies by material and part.
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4ProductionStandard production runs ship about 2 weeks after drawing approval, on flatbed die-cutting, CNC knife cutting for kiss-cut gasket sets, slitting for strip stock, waterjet cutting for thick sections, and kitting for per-unit gasket kits. Ongoing parts run with material traceability and lot-code TDS records.
Where H-O parts do the work
Six sealing jobs cover the wet side of an HVAC system: the compressor flange, where refrigerant and oil are most concentrated; the service valves and fittings a technician remakes for the life of the machine; the oil-exposed joints that live in POE or PAG; the chilled-water and glycol loop, where the chemistry flips; the condensate pan, wet by design; and the low-GWP transition, which re-opens every one of them.
Click a tab to see the exposure, the constraint, and the material families H-O converts for that job.
Compressor flange gaskets
The compressor is where the system's two fluids are most concentrated and most hostile at once: refrigerant gas at pressure and the lubricating oil that travels with it, both at the temperature the compression cycle produces. A bolted terminal-box flange, a head gasket, a mounting-foot or service-port gasket on a reciprocating, scroll, or screw compressor has to hold that refrigerant-and-oil mixture for the life of the machine without swelling, hardening, or extruding out of the joint.
The elastomer is chosen from the fluid pair, not from the flange size, and the pairing is read from the vendor TDS compatibility tables rather than assumed from a family name.
What H-O converts. Die-cut flange gaskets, terminal-box and head gaskets, washers, and bolt-patterned cover gaskets from HNBR (60/70/80 durometer) and neoprene (CR) by designation, with FKM/Viton® stepping in where the refrigerant-and-oil pair runs hot or aggressive enough that the vendor TDS compatibility tables put nitrile chemistry out of range.
Reinforced bolted covers take rubberized cork or cloth-inserted nitrile where the joint needs extrusion resistance. Parts ship to the flange drawing through flatbed die-cutting and waterjet cutting for thick sections.
Material guidance. HNBR is the common workhorse for refrigerant-oil flanges: its saturated backbone gives measurably better heat and oil aging than standard nitrile, with ASTM D2000 line callouts on the grade TDS and three durometers covering soft conformable covers (60) through firm high-bolt-load flanges (80). Neoprene is specified by designation where its balance of refrigerant behavior and cost suits the joint.
The controlling discipline is the same in every case: confirm the candidate grade against the vendor TDS compatibility tables for the actual refrigerant-and-oil pair and the joint temperature, because the same compound can pass one mixture and fail another. Performance depends on grade, geometry, compression, and environment; final material selection should be validated in the application.
Grade-level properties, standards and caveats for these families are in the material reference below — one card per family, with the TDS links.
Flange and cover drawings with bolt patterns and compressed-thickness targets, the refrigerant designation (per ASHRAE 34) and the lubricant type (POE, PAG, mineral), the operating temperature and pressure at the joint, lengths and quantities per unit, and whether gaskets mount dry or with adhesive backing. Name both fluids; the compatibility review needs the pair.
Service-valve & fitting seals
Every place the refrigerant circuit can be opened, charged, or measured is a sealed joint that a technician will break and remake over the system's life: service valves, Schrader-style access ports, sight-glass and sensor fittings, flare and union backups.
These seals are small, but they are the joints most often disturbed in the field, so they have to seal on the first remake and the fortieth without taking a set or hardening in the refrigerant-and-oil stream. The fluid pair and the service temperature pick the chemistry; the joint geometry picks the form.
What H-O converts. Die-cut and kiss-cut gaskets, backup washers, bonnet and cap seals, and flat seals for valve bodies and fitting faces from HNBR and FKM/Viton® by designation, with Viton® sponge 1628 where a conformable closed-cell form is needed at low closure force and FFKM reserved for the small number of joints whose fluid list is aggressive enough that the FKM compatibility margin is in question. Small precision parts run through CNC knife cutting and ship kiss-cut on liner.
Material guidance. FKM is the family to reach for when HNBR's heat ceiling or a more aggressive refrigerant-and-oil pair is the limiting line on the TDS comparison; its TDS lists the service-temperature range and the immersion behavior, and the conformable sponge form seats at the low loads a small fitting actually produces. FFKM is priced like the extreme-duty material it is, so it is specified surgically: one aggressive port on an otherwise-HNBR system, not the whole valve set.
As with every job on this page, the refrigerant-and-oil compatibility is read from the vendor TDS compatibility tables for the named fluids, not from the family name.
Grade-level properties, standards and caveats for these families are in the material reference below — one card per family, with the TDS links.
Valve-body and fitting drawings or the maker and model, the refrigerant and oil the port sees, the remake frequency expected in service, seal cross-sections and gland dimensions, the operating temperature, and per-unit quantities. Note any joint that sees a different or more concentrated fluid than the rest of the circuit.
POE/PAG oil-exposed gaskets
The lubricant is the quiet half of the fluid pair, and it is the half that surprises people. Modern systems run synthetic oils, polyolester (POE) on many HFC and low-GWP systems and polyalkylene glycol (PAG) on others, and these synthetics are chemically different from the mineral oils older compounds were tuned for. An elastomer that shrugs off mineral oil can swell or extract in POE or PAG, and the failure shows up not at commissioning but months later as a softened, weeping gasket.
Oil-exposed seals at the oil separator, sight glass, sump, and crankcase are specified from the oil's own immersion data, not from a generic "oil-resistant" label.
What H-O converts. Die-cut sump, separator, sight-glass, and crankcase gaskets, washers, and flat seals from HNBR, FKM/Viton®, and solid nitrile (NBR) by durometer, with the grade chosen from the lubricant's TDS immersion table. Reinforced and bolted-cover duty takes rubberized cork where compressibility and recovery carry the seal. Parts run through flatbed die-cutting with bolt patterns to drawing.
Material guidance. "Oil-resistant" is not one property: a compound tuned for petroleum mineral oil can behave differently in POE or PAG, so the honest predictor is the grade's immersion data per ASTM D471 for the actual synthetic, read off the vendor TDS compatibility tables. HNBR is the common first answer for hot synthetic-oil duty; FKM extends the range where the oil and temperature push past it.
Where the TDS is silent on a specific lubricant, a coupon immersion in the actual oil is the honest answer rather than a family-level assumption. Final material selection should be validated in the application.
Grade-level properties, standards and caveats for these families are in the material reference below — one card per family, with the TDS links.
The lubricant type and grade (POE, PAG, mineral, or the OEM oil designation), the refrigerant it travels with, the operating temperature at the joint, the gasket drawings and compressed-thickness targets, and per-unit quantities. If the oil is a proprietary blend, send its name so the review runs against the maker's immersion data.
Chilled-water & glycol-loop gaskets
The hydronic side of a chiller or heat pump is a different chemistry problem entirely, and the family that wins here is the one that loses on the refrigerant side. Chilled-water headers, glycol-loop flanges, pump and valve bodies, heat-exchanger end-bells, and strainer covers carry water and water-glycol mixtures, sometimes with corrosion inhibitors, often outdoors and cold. EPDM is at home in exactly this duty: the same non-polar backbone that makes it swell in mineral oil is what makes it indifferent to hot water, glycol, and ozone.
Keeping EPDM in the water zones and out of the oil zones is the single most important family-boundary discipline on this page.
What H-O converts. Die-cut flange and end-bell gaskets, pump-body and valve-cover gaskets, strainer and header gaskets, and slit strip from EPDM solid by designation and EPDM sponge for the compressible joints. Potable-water-contact duty in equipment that touches drinking water specifies 576 NSF-certified EPDM, whose TDS cites the NSF/ANSI 61 designation. Thick sections cut clean on waterjet; strip comes off slitting.
Material guidance. EPDM owns water and glycol; its ozone and weathering behavior is reported on the grade TDSs and its compression classes per ASTM D1056 match flange closure forces. The named coolant and its concentration are the spec, not "glycol" as a category: an inhibited propylene-glycol mixture and an ethylene-glycol mixture can interact differently with the elastomer, and the pairing is confirmed against the fluid maker's compatibility data.
Where a circuit genuinely sees both water and oil mist, the joint moves up to FKM, which covers both duties. Final material selection should be validated in the application.
Grade-level properties, standards and caveats for these families are in the material reference below — one card per family, with the TDS links.
The named coolant chemistry and concentration (water, ethylene or propylene glycol percentage, inhibitor package), the flange or end-bell drawings, the operating temperature and pressure, whether the equipment touches potable water (for the NSF designation), compressed-thickness targets, and per-unit quantities.
Condensate-pan seals
Below the coil sits the part of the system that is wet by design: the condensate pan, where water collects, sits, and drains, often with a faintly acidic or biologically active character and standing moisture for the life of the unit.
Pan-to-casing seals, drain-fitting gaskets, secondary-pan seals, and the joint between pan sections have to hold water that lingers for the life of the unit, resist the microbial and mild-chemical environment that standing condensate develops, and keep their seal where a leak means water inside the cabinet or onto the ceiling below.
The duty is wet, cool, and patient, which is exactly EPDM's home ground.
What H-O converts. Die-cut pan-perimeter gaskets, drain-fitting and grommet seals, secondary-pan gaskets, and slit strip from EPDM sponge and EPDM solid by designation, with cork-nitrile (rubberized cork) cut to the pan profile where a compressible composite gasket suits the bolted joint, and closed-cell foam where a low-closure-force pan seam needs a conformable layer. Parts ship and kiss-cut to the pan drawing through flatbed die-cutting and CNC knife cutting.
Material guidance. EPDM is the common default for condensate duty because its water and ozone resistance is reported on the grade TDSs and it does not feed the biological growth standing water encourages the way some organic foams can. Closed-cell construction matters: the seal must not wick condensate along its own length. Cork-nitrile suits bolted pan joints where compressibility and recovery do the work.
Keep the family in the water track; the refrigerant-and-oil families have no advantage here and the wrong cell structure invites wicking. Final material selection should be validated in the application.
Grade-level properties, standards and caveats for these families are in the material reference below — one card per family, with the TDS links.
Pan and drain-fitting drawings with seal cross-sections, the pan material and finish, whether the seal mounts dry or with adhesive backing, the joint closure force if known, gasket thicknesses, and per-unit quantities. Note any condensate-treatment chemistry the pan carries.
Low-GWP refrigerant transition guidance
The refrigerant under the gasket is changing. The move to lower global-warming-potential refrigerants is putting A2L lower-flammability refrigerants and new low-GWP blends into equipment that used to run older HFCs, and a seal qualified against one refrigerant carries no automatic standing in another.
This job is a review rather than a single material answer: when a platform changes refrigerant, every wet-side seal on it has to be re-checked against the new refrigerant-and-oil pair, by designation, using the vendor TDS compatibility tables, because the elastomer that held the old fluid may or may not hold the new one.
What H-O converts. The same family set the rest of this page covers, re-selected for the new fluid pair: HNBR, FKM/Viton®, neoprene, and EPDM by designation, with A2L-adjacent material reviews done against the vendor TDS compatibility tables for the named low-GWP refrigerant and its lubricant. H-O converts the chosen material and supplies its TDS and lot-code documentation; the refrigerant pairing rests on the vendor compatibility data, and the refrigerant safety class (per ASHRAE 34, including A2L) belongs to the refrigerant, not to the gasket.
Material guidance. Treat a refrigerant change as a full seal re-review, not a substitution. Name the new refrigerant by its ASHRAE 34 designation and its safety class, name the new lubricant, and re-run each seal location against the vendor TDS compatibility tables for that pair.
Where a UL 94 flame class is called on a seal material near an A2L charge, the listing is per grade and per thickness on the TDS and rides alongside the compatibility requirement rather than replacing it; H-O does not certify or approve materials against flammability of the charged system, which belongs to the equipment maker's own evaluation.
Final material selection should be validated in the application.
Grade-level properties, standards and caveats for these families are in the material reference below — one card per family, with the TDS links.
A2L is a refrigerant safety class, not a material rating. The A2L designation (per ASHRAE 34) describes the refrigerant's lower flammability and toxicity, and the system-level flammability evaluation belongs to the equipment maker. The gasket's contribution is documented material properties: an ASTM D2000 class on the TDS, ASTM D471 immersion behavior for the named refrigerant-and-oil pair, and a UL 94 flame class where the grade lists one. H-O cites all of these by designation and does not certify the charged system.
Five decisions that drive a refrigerant-and-oil seal spec
Wet-side sealing is not a single-property choice. The right gasket satisfies several independent constraints at once, and missing one produces a seal that passes the factory leak check, ships fine, and weeps a year later after the elastomer has swollen, hardened, or lost recovery in service. Read the five factors below in order; each one constrains the others.
Match the elastomer to the fluid pair, not to the part name. "Refrigerant-resistant" and "oil-resistant" are not single properties: a compound tuned for one refrigerant-and-oil combination can behave differently in another, and the EPDM that thrives in a glycol loop swells in refrigerant oil. Read both fluids off the equipment spec, then read the family's behavior off the vendor TDS compatibility tables and its ASTM D471 immersion data before anything else.
Show all 5 selection factors tap to expand
1. The fluid pair decides the chemistry
Name the actual refrigerant and the actual lubricant, not the categories. The refrigerant and the oil travel together, and the elastomer answer comes from the pair: nitrile and HNBR handle many refrigerant-oil combinations, FKM covers the hotter and more aggressive ones, EPDM owns water and glycol but swells in oil. Write the refrigerant (by ASHRAE 34 designation), the lubricant, its concentration, and any cleaning chemistry on the drawing, and verify the family against its TDS compatibility tables per ASTM D471. [2]
2. Temperature can disqualify the fluid's first answer
A compound that handles the fluid cold can fail it hot: heat accelerates swell and hardening, and aging follows the methods on the TDS. Standard nitrile serves general oil duty; sustained elevated temperature moves the spec to HNBR, whose hydrogenated backbone is the reason the grade exists; FKM lists its service range on the TDS for the hot end. State the continuous temperature at the gasket, not the room ambient, and confirm the family's TDS range covers it with margin. [1]
3. Bolted-flange mechanics: compressibility and recovery
A compressor or pump cover seals because the gasket compresses to follow flange waviness and recovers as bolts relax and the machine thermal-cycles. Homogeneous elastomer sheet seals by elastic deformation and needs flatter flanges or higher bolt load; rubberized cork is engineered for compressibility and recovery at modest loads; cloth-inserted constructions resist extrusion on heavy covers. Match the construction to the flange stiffness and bolt pattern, and put the compressed thickness on the drawing. Cellular classes per ASTM D1056. [3]
4. The refrigerant safety class is the refrigerant's, not the seal's
The low-GWP transition puts A2L lower-flammability refrigerants into more equipment, and the ASHRAE 34 safety class describes the refrigerant, not the gasket. The system-level flammability evaluation belongs to the equipment maker. Where a UL 94 flame class is called on a seal material near an A2L charge, the listing is per grade and per thickness on the TDS and rides alongside the compatibility requirement. Name the refrigerant designation and class on the drawing; the gasket is cited by its own material designations. [4]
5. Service life: aging beyond the fluid itself
Outdoor and mechanical-room service adds aging paths the immersion table does not show: ozone cracking on the weather side, heat aging, and compression set that lets a long-installed gasket take a permanent squeeze and lose recovery. For decades-long equipment service, weigh recovery and aging data as heavily as the day-one immersion numbers, and ask for the lot-code TDS records H-O keeps with each shipment. When a system changes refrigerant or oil, re-review the seals; a seal qualified against one fluid carries no automatic standing in another. [2]
Specification Tools
Two tools to take you from "we're sealing a refrigerant-and-oil system" to here's the converted-parts checklist for the drawing set: a refrigerant-duty checklist builder that assembles the part list with its citations, and a side-by-side comparison of every elastomer family on this page.
1. Refrigerant-and-oil seal checklist builder
Check the sealing points your system carries. The builder assembles the corresponding converted parts into a checklist with the family, what to send with the drawing, and the citation language (elastomer classes per ASTM D2000 on the vendor TDS; refrigerant safety class per ASHRAE 34 by designation; compatibility per vendor TDS compatibility tables). The default selection below is pre-built for a typical refrigeration system; every part is also printed in the material reference section, so nothing here exists only behind a script.
Seal checklist: 3 parts selected
Each checked sealing point adds its part below. The list is the starting bill of materials for the compatibility review, not a certification: elastomer classes (ASTM D2000) and immersion behavior (ASTM D471) come from the grade TDS, refrigerant safety classes (ASHRAE 34, incl. A2L) are cited by designation, and refrigerant-and-oil compatibility is read from the vendor TDS compatibility tables for the named fluid pair.
- Compressor flange gaskets: HNBR by durometer (neoprene by designation; FKM where hot/aggressive)Send: flange drawings, bolt patterns, refrigerant + oil, joint temperature/pressure. Cite: ASTM D2000 class per TDS; compatibility per vendor TDS tables.
- Service-valve & fitting seals: HNBR / FKMViton by designationSend: valve/fitting drawings, fluid pair, remake frequency, gland dimensions. Cite: ASTM D471 immersion per TDS; compatibility per vendor TDS tables.
- Condensate-pan seals: EPDM sponge / solid, cork-nitrile to the pan profileSend: pan and drain drawings, seal cross-sections, mounting style. Cite: ASTM D1056 classes per TDS; closed-cell construction against wicking.
2. Side-by-side: fluid-sealing family comparison matrix
Every elastomer family called out on this page, with construction, the property that drives its selection, the standards its TDS cites, and the sealing job it serves. Click a column header to sort. Click any material name to jump to its accordion entry. Compatibility classes are family-level starting points; the vendor TDS compatibility tables govern for the named fluid pair.
| Material | Construction | Selection driver | Standards on the TDS / by designation | Sealing job | |
|---|---|---|---|---|---|
| The refrigerant-and-oil track (compressor, valves, oil side) | |||||
| HNBR Hydrogenated Nitrile (60/70/80 Durometer)Solid elastomer | Solid HNBR sheet | Hot refrigerant-oil headroom | ASTM D2000 line callouts per grade TDS | Compressor flanges, oil side | |
| FKM / Viton® (75D Solid, Sponge 1628)Fluoroelastomer | Solid + closed-cell sponge | Hot or aggressive fluid pairs | ASTM D2000; TDS temperature range | Hot valves, oil, aggressive ports | |
| Neoprene (CR) Foam & SolidPolychloroprene | Solid + closed-cell foam | Balanced refrigerant duty at cost | ASTM D1056 / D2000 per grade TDS | Compressor, general flanges | |
| Nitrile NBR (Commercial / Transformer-Oil / Bio-Diesel Grades)Solid elastomer | Solid NBR sheet | General petroleum-oil duty | ASTM D2000, D471 per grade TDS | Oil-side gaskets, washers | |
| FFKM Perfluoroelastomer (GP 70/75D, Steam 75D)Perfluoroelastomer | Solid elastomer | Near-universal chemistry, extreme duty | Maker TDS compatibility tables | Aggressive ports (surgical use) | |
| The water-and-condensate track (glycol loops, pans) | |||||
| EPDM Solid (Industrial & 576 NSF Grades)Ethylene-propylene | Solid elastomer | Water/glycol & weather, kept off oil | ASTM D2000; NSF/ANSI 61 designation (576) | Glycol loops, water flanges | |
| EPDM SpongeSponge rubber | Closed-cell EPDM sponge | Compressible water-side sealing | ASTM D1056 classes per grade TDS | Condensate pans, compressible joints | |
| Rubberized & Technical Cork (cork-nitrile)Cork-elastomer composite | Cork granule + elastomer binder | Compressibility & recovery at bolt loads | ASTM F36 / F146 compressibility & immersion | Bolted covers, pan joints | |
| BISCO® Cellular Silicone (warm dry side)Silicone foam/sponge | Cellular silicone | Temperature endurance, dry duty | UL 94 listings per grade TDS | Warm dry-side gaskets | |
Skip ahead and request your compatibility review now
If your drawing set already calls out an HNBR durometer, an FKM grade, a neoprene gasket, an EPDM glycol-loop gasket, or a condensate-pan seal, send it over with the refrigerant and oil named for review against the vendor TDS compatibility tables.
Refrigerant-and-oil seal failures you can prevent at spec
Wet-side seal failures rarely show at the factory leak check. The gasket seats, the joint torques down, the test passes. Then it weeps months or years later, after the elastomer has swollen in a fluid it was not compounded for, hardened in heat, or relaxed below its sealing stress. Five patterns cover most of what fails on this page, and each is a specification decision made before the parts are cut.
Fluid attack is slow and one-way. Swell, hardening, and extraction play out over weeks to years and do not reverse. The fix is at spec, against the vendor TDS compatibility tables and ASTM D471 immersion data for the named refrigerant-and-oil pair, not at the return bench. Refrigerant-and-oil compatibility is read from the vendor tables, not assumed from a family name.
Show all 5 failure modes tap to expand
1. The gasket swelled because "oil-resistant" was read as one property
A nitrile compound tuned for petroleum mineral oil goes into service against a POE or PAG synthetic, and the immersion behavior is different: volume swell climbs, hardness drops, and the cover begins to weep at the bolt spacing. The mechanism is chemistry, not quality: ASTM D471 immersion data is fluid-specific, and a compound is only as resistant as its data in your actual lubricant.
The fix: name the refrigerant and the lubricant on the drawing, and select the grade whose vendor TDS compatibility tables cover that pair, HNBR or FKM where the oil and temperature push past standard nitrile. [2]
2. EPDM went where oil lives (or nitrile went where water lives)
The two most common cross-family substitutions both fail. EPDM in refrigerant oil swells dramatically: the same non-polar backbone that makes it indifferent to water and glycol soaks up the lubricant. Nitrile in a chilled-water or glycol loop has no advantage and craze-cracks in outdoor ozone. The fix: hold the family boundary.
The refrigerant-and-oil track takes nitrile, HNBR, neoprene, and FKM; the water, glycol, and condensate track takes EPDM; and a joint that genuinely sees both (oil mist plus water) moves up to FKM, whose TDS covers both duties. [1]
3. The cover gasket lost its squeeze: compressibility and recovery ignored
A compressor or pump cover gasket is a spring as much as a seal.
Specify one too hard for the flange and bolt load and it cannot conform to flange waviness; specify one with poor recovery and thermal breathing plus bolt relaxation walk the sealing stress down until the joint weeps. The fix: match gasket construction to flange stiffness and bolt pattern, specify compressed thickness on the drawing, use rubberized cork where compressibility and recovery carry the seal, and move to a reinforced construction for heavy bolted covers that would otherwise extrude.
Cellular classes per ASTM D1056. [3]
4. A refrigerant change reused a seal that no longer qualified
A platform moved from an older HFC to a low-GWP or A2L refrigerant, the oil changed with it, and the existing seal drawing was carried over unchanged, because it had worked before. A seal qualified against one refrigerant-and-oil pair carries no automatic standing in another, and the failure reads as mysterious because nothing in the geometry changed. The fix: treat a refrigerant change as a full seal re-review.
Name the new refrigerant by its ASHRAE 34 designation and safety class, name the new lubricant, and re-run each seal location against the vendor TDS compatibility tables for that pair; the families may hold, the grades may not. [4]
5. The condensate seal wicked, or fed what grows in standing water
A pan seal cut from the wrong cell structure wicks condensate along its own length, carrying water past the joint it was meant to close; an organic open-cell foam in standing condensate can also become a substrate for the biological growth a wet pan develops.
The leak shows up as water inside the cabinet or on the ceiling below. The fix: keep condensate seals closed-cell and in the EPDM family whose water and ozone resistance is reported on the TDS, or use cork-nitrile cut to the pan profile for bolted joints; size by closure force per ASTM D1056 and validate in the application.
Material reference
Detailed specs for the elastomer families referenced on this page: the refrigerant-and-oil track (HNBR by durometer, FKM/Viton®, neoprene, solid nitrile, and FFKM for the extreme end), and the water-and-condensate track (EPDM solid and sponge, cork-nitrile, and cellular silicone for the warm dry side).
Values are per the vendor TDS on file for each grade with the method named; refrigerant-and-oil compatibility is reviewed against the vendor TDS compatibility tables and ASTM D471 immersion data, not assumed. H-O die-cuts, kiss-cuts, slits, and kits every family to drawing.
HNBR Hydrogenated Nitrile (60 / 70 / 80 Durometer)Compressor & oil-side gaskets · ASTM D2000 line callouts per grade TDS
HNBR is the honest middle answer: better than NBR in heat, not an FKM substitute in aggressive chemistry. Put the ASTM D2000 line callout, durometer, and thickness on the drawing, and confirm the grade against the vendor TDS compatibility tables for the actual refrigerant-and-oil pair.
FKM / Viton® (75D Solid, Sponge 1628)Hot & aggressive fluid pairs · ASTM D2000; TDS temperature range
Specify form first (solid vs sponge), then the ASTM D2000 designation where the drawing requires it. As with every family here, refrigerant-and-oil compatibility is read from the vendor TDS compatibility tables for the named fluids, not from the family name.
Neoprene (CR) Foam & SolidCompressor & general flange gaskets · ASTM D1056 / D2000 per grade TDS
Neoprene is specified by designation against the refrigerant-and-oil pair, not as a blanket "refrigerant-compatible" claim. Pick the closed-cell class to the closure force per ASTM D1056 for foam and the line callout per ASTM D2000 for solid.
EPDM Solid (Industrial Grades + 576 NSF-Certified)Chilled-water, glycol & condensate · ASTM D2000; NSF/ANSI 61 designation (576)
Keep EPDM in the water track and out of the oil zones; that family boundary is the single most important discipline on this page. The named coolant and its concentration are the spec, confirmed against the fluid maker's compatibility data.
EPDM SpongeCondensate pans & compressible water-side joints · ASTM D1056 classes per grade TDS
Pick the closed-cell class to the closure force as with every ASTM D1056 material; closed-cell construction is the controlling property against wicking in standing condensate.
Solid Nitrile (NBR), FFKM, Rubberized Cork & Cellular SiliconeOil-side, extreme-duty, bolted-cover & warm dry-side families · methods per grade TDS
These four families round out the catalog this page draws from. NBR, cork, and silicone are workhorses with clear lanes; FFKM is the priced-like-it extreme-duty answer used surgically. Refrigerant-and-oil compatibility for any of them is read from the vendor TDS compatibility tables for the named fluid pair.
Refrigerant, oil & coolant sealing: engineer-grade FAQ
Ten of the questions we hear most from compressor, chiller, and refrigeration teams. If your question isn't here, send a drawing with the refrigerant and oil named, or call, engineering picks up.
Is this gasket compatible with R-454B (or another named refrigerant)?
That is a question for the vendor TDS compatibility tables, not for a family name. H-O does not publish blanket compatibility claims against a named refrigerant; instead, engineering reads the candidate grade against the vendor compatibility tables for the actual refrigerant-and-oil pair, supported by ASTM D471 immersion behavior on the grade TDS. Name both fluids on the drawing and the review runs against data. Where the table is silent on your specific pair, a coupon immersion in the actual fluids is the honest answer. [2]
Why do I have to name the oil and not just the refrigerant?
Because the seal sees both. The refrigerant and the lubricant travel together through the circuit, and the oil is the half that most often surprises people: a synthetic POE or PAG is chemically different from the mineral oils older compounds were tuned for, and an elastomer that shrugs off one can swell or extract in another. The compatibility review needs the pair, the refrigerant by its designation and the lubricant by type or OEM grade, read against the vendor TDS compatibility tables.
HNBR or FKM for a compressor flange: how do I choose?
By temperature and by the fluid pair. HNBR is the common workhorse for refrigerant-oil flanges, with better heat and oil aging than standard nitrile and an ASTM D2000 line callout on the grade TDS. Move to FKM/Viton when HNBR's heat ceiling or a more aggressive refrigerant-and-oil pair is the limiting line on the vendor TDS comparison. Match the durometer and compression to the real bolt load either way, and confirm the choice against the vendor TDS compatibility tables for the named fluids. [1]
Can EPDM be used on the refrigerant side?
Generally no, and the reason is chemistry rather than quality. EPDM's non-polar backbone is what makes it indifferent to water, glycol, and ozone, and the same backbone soaks up refrigerant oils and swells. Keep EPDM in the water-and-condensate track (chilled-water headers, glycol loops, condensate pans) and out of the compressor, valve, and oil zones, which take nitrile, HNBR, neoprene, or FKM. A joint that genuinely sees both water and oil mist moves up to FKM, whose TDS covers both duties.
What does A2L mean for the gasket material?
A2L is a refrigerant safety class, not a material rating. The designation, per ASHRAE 34, describes the refrigerant's lower flammability and toxicity, and the system-level flammability evaluation belongs to the equipment maker. The gasket's contribution is documented material properties: an ASTM D2000 class on the TDS, ASTM D471 immersion behavior for the named refrigerant-and-oil pair, and a UL 94 flame class where the grade lists one, per grade and per thickness. H-O cites all of these by designation and does not certify the charged system. [4]
We're changing refrigerant. Do the seals need to be re-reviewed?
Yes, and it is a cheap review compared to the alternative. A seal qualified against one refrigerant-and-oil pair carries no automatic standing in another; the oil usually changes with the refrigerant, and different chemistries interact differently with every elastomer family. Send the new refrigerant by its ASHRAE 34 designation, the new lubricant, and the existing seal drawings; engineering re-runs each location against the vendor TDS compatibility tables. The families may hold, the grades may not. [4]
What seals a chilled-water or glycol loop?
EPDM, by designation. The hydronic side carries water and water-glycol mixtures, and EPDM is at home there: its ozone and weathering behavior is reported on the grade TDSs, and its compression classes per ASTM D1056 match flange closure forces. The named coolant and its concentration are the spec, not 'glycol' as a category, since an inhibited propylene-glycol mixture and an ethylene-glycol mixture can interact differently with the elastomer. Equipment that touches potable water specifies the 576 NSF-certified EPDM for the NSF/ANSI 61 designation. [3]
What material is right for a condensate pan?
A closed-cell EPDM sponge or solid, or cork-nitrile cut to the pan profile for bolted joints. Condensate duty is wet, cool, and patient, with standing water that can be faintly acidic or biologically active, so the seal has to resist that environment and must not wick water along its own length, which is why closed-cell construction matters.
EPDM's water and ozone resistance is reported on the grade TDS, and it does not feed biological growth the way some organic open-cell foams can. Size by closure force per ASTM D1056 and validate in the application. [3]
Will adhesive-backed seals stick to the equipment surface?
Often, with the right PSA, but it has to be validated rather than assumed. Adhesive-backed gasket performance depends on the substrate, its surface energy and preparation, temperature, exposure, dwell time, applied pressure, joint geometry, and assembly method, and refrigerant oils and condensate at the joint add a chemical variable.
Validate the adhesive system on the actual surface before the part is released; H-O laminates the PSA grade your validation selects and documents it per the adhesive vendor's TDS. A sample part is the fastest path to a recommendation.
Can H-O kit the whole wet-side gasket set, and does H-O mold or extrude?
Yes to kitting: compressor flange gaskets, valve and fitting seals, oil-side gaskets, glycol-loop gaskets, and condensate-pan seals can ship as one kit per unit, parts on liner in assembly order, with lot-code TDS records per material. H-O and converts sheet, roll, and strip stock to drawing; we do not mold or extrude in-house, and molded or extruded profiles are coordinated through a partner network. Conversion runs in Winsted, Connecticut under an ISO 9001:2015 certified quality management system.
Glossary: terms used on this page
Quick reference for the refrigerant, oil, and elastomer terminology used throughout. Each entry links to the relevant standard or method where applicable.
ASHRAE 34 / refrigerant safety class (by designation)
The standard that assigns refrigerant designations (the R-number) and safety classifications by toxicity and flammability, per [4]. The A2L class denotes lower toxicity and lower flammability. The class belongs to the refrigerant; on this page it is cited by designation, and the system-level flammability evaluation belongs to the equipment maker.
A2L refrigerant
A refrigerant in the lower-flammability, lower-toxicity safety class under ASHRAE 34, common in the low-GWP transition. A2L is a refrigerant property, not a material rating; gasket materials near an A2L charge are cited by their own designations (ASTM D2000 class, UL 94 flame class per grade TDS), and compatibility is read from the vendor TDS compatibility tables.
GWP (global warming potential)
A measure of a refrigerant's climate impact relative to carbon dioxide. The move to lower-GWP refrigerants is the driver behind the transition reviews on this page: changing the refrigerant usually changes the oil, and a seal qualified against the old pair has to be re-reviewed against the new one.
POE oil (polyolester)
A synthetic lubricant used with many HFC and low-GWP refrigerants. POE is chemically different from mineral oil, so an elastomer suited to mineral oil is not automatically suited to POE; the gasket grade is selected from the oil's TDS immersion data per ASTM D471.
PAG oil (polyalkylene glycol)
A synthetic refrigerant lubricant common in certain systems. Like POE, PAG is a synthetic whose interaction with an elastomer is read from the vendor TDS compatibility tables rather than assumed from a generic oil-resistance label.
ASTM D2000 line callout
The standard classification system for rubber materials in automotive and industrial applications, per ASTM D2000 [1]. The coded line callout on the drawing names the elastomer type, hardness, and property requirements; HNBR, NBR, neoprene, FKM, and EPDM grades carry their D2000 designations on the TDS.
ASTM D471 (effect of liquids)
Rubber Property, Effect of Liquids, per ASTM D471 [2]: coupons are immersed in the service fluid at a defined temperature and time, and the change in volume, hardness, and tensile is reported. The method behind every compatibility statement on this page; where the TDS is silent on a fluid pair, a coupon immersion is the honest answer.
ASTM D1056 compression class
The classification for flexible cellular materials (sponge and expanded rubber) per ASTM D1056 [3], grouping grades by the pressure needed to compress them. The number that matches a foam or sponge seal to its real closure force, reported on the neoprene and EPDM sponge grade TDSs.
HNBR (hydrogenated nitrile)
Acrylonitrile-butadiene rubber with a hydrogenated, saturated backbone, giving measurably better heat and oil aging than standard NBR. The common workhorse for elevated-temperature refrigerant-oil flanges, available in 60, 70, and 80 durometer with ASTM D2000 callouts on the TDS.
FKM / Viton® (fluoroelastomer)
A fluoroelastomer family with a wide service-temperature range and broad fluid resistance, in solid and closed-cell sponge forms. The step past HNBR for hot or aggressive refrigerant-and-oil pairs; compatibility for the specific fluids is read from the vendor TDS tables.
EPDM (ethylene-propylene-diene monomer)
An elastomer with a non-polar backbone that is indifferent to water, glycol, and ozone but swells in refrigerant oil. The family for chilled-water, glycol-loop, and condensate-pan duty, and deliberately kept out of the oil zones. The 576 grade is NSF-certified for potable-water contact.
Cork-nitrile (rubberized cork)
Cork granules bound in a nitrile or other elastomer binder, giving controlled compressibility from the cork phase and oil resistance from the binder. Specified for bolted compressor covers and condensate-pan joints where compress-and-recover behavior carries the seal; compressibility per ASTM F36, immersion per ASTM F146 on the TDS.
Kiss-cut
Die-cutting through the material but not its release liner, so adhesive-backed seals peel off a sheet in assembly order. The standard ship format for valve-seal and gasket sets that mount with a PSA.
Last updated · Reviewed by H-O Products engineering (ISO 9001:2015 certified converter, Winsted, CT).
Standards, test methods & technical references
The standards, methods, and vendor technical data sheets cited throughout this page. Refrigerant designation and safety classes are cited by designation: they belong to the refrigerant, and the system-level evaluation belongs to the equipment maker. Refrigerant-and-oil compatibility is read from the vendor TDS compatibility tables. Standards editions current as of June 2026; verify against the publishing body before final spec.
H-O converts materials tested to the material-level methods on the source vendor's TDS; H-O does not certify systems, refrigerants, or independently certify materials.
[1] ASTM D2000
Standard Classification System for Rubber Products in Automotive Applications, published by ASTM International. The line-call classification framework behind the HNBR, NBR, neoprene, FKM, and EPDM designations cited on the grade TDSs.
[2] ASTM D471
Standard Test Method for Rubber Property — Effect of Liquids, published by ASTM International. The fluid-immersion method behind every refrigerant-and-oil compatibility statement on this page; results are reported on the maker TDS for the fluids tested.
[3] ASTM D1056
Standard Specification for Flexible Cellular Materials — Sponge or Expanded Rubber, published by ASTM International. The classification and method framework behind the neoprene and EPDM sponge compression classes cited on the grade TDSs.
[4] ASHRAE 34 (by designation)
Designation and Safety Classification of Refrigerants, published by ASHRAE. The framework that assigns refrigerant R-numbers and toxicity/flammability safety classes, including the A2L lower-flammability class. Cited by designation only; the class belongs to the refrigerant, and the system-level flammability evaluation belongs to the equipment maker.
[5] UL 94 (classes per grade TDS)
Standard for Tests for Flammability of Plastic Materials for Parts in Devices and Appliances, published by UL. Flammability classes (including V-0) belong to the listed material grades per their vendor TDSs; this page cites them only where the grade's own TDS reports them, per grade and per thickness.
Updated . Standards editions current at publication; verify against the publishing body before final spec. H-O converts materials tested to the methods cited; H-O does not certify systems or refrigerants. Lot-specific documentation available on request.
Get a refrigerant, oil & coolant sealing engineering quote
Send a drawing set, part sample, or system spec with the refrigerant and oil named. We typically respond within one business day with a material recommendation, prototype lead time, and TDS compatibility verification against your fluid pair, temperature, and pressure.
See also: related H-O application pages
Engineering content for the adjacent fluid-sealing sub-application, sibling HVAC sub-applications, the converting capabilities behind these parts, and the owning industry hub. Each page covers material selection, failure modes, and converter-side process detail for its application family.
Material data & standards. All hardness, temperature, and compatibility values on this page are taken from the source vendor's technical data sheets with the method named (ASTM D2000 line callouts, ASTM D471 fluid immersion, ASTM D1056 cellular classes; UL 94 flame classes per the listed grade TDSs).
Refrigerant designation and safety classes (ASHRAE 34, including the A2L lower-flammability class) are cited by designation only: they describe the refrigerant, the safety class belongs to the refrigerant, and the system-level flammability evaluation belongs to the equipment maker.
Refrigerant-and-oil compatibility is read from the vendor TDS compatibility tables for the named fluid pair, not claimed as a blanket family property. H-O converts materials; H-O does not design systems, select refrigerants, certify systems, or independently certify materials against the standards cited. Performance depends on grade, geometry, compression, and environment; final material selection should be validated in the application against the vendor TDS.
Conversion scope. H-O and converts sheet, roll, and strip stock to drawing in Winsted, Connecticut: die-cut and kiss-cut gaskets, washers, and seals, slit strip, waterjet-cut thick sections, and kitted per-unit wet-side gasket sets, with material traceability and lot-code TDS records. H-O does not mold or extrude in-house; molded or extruded profiles are coordinated through a partner network. Lead-time and MOQ details are in the process strip and the quote form above.