What does a filter drier do? A filter drier traps moisture, acid and dirt in the refrigerant before they reach the metering device and compressor. Sporlan rates liquid line driers at a 1 psi pressure drop, and Danfoss says to replace the drier each time the system is opened.
Key Takeaways
- Danfoss: “The filter drier should be replaced each time the refrigeration system is opened” (Danfoss technical article).
- Sporlan rates a liquid line drier’s flow capacity at a 1 psi pressure drop with 86°F liquid, under AHRI Standard 710 (Sporlan Bulletin 40-10).
- For R-410A air conditioning, Sporlan caps suction line drier pressure drop at 3 psi permanent and 8 psi temporary.
- Standard driers must never see reverse flow; heat pumps use bi-flow models such as Sporlan HPC, Danfoss DMB and Copeland BFK.
- Copeland sizes driers at 9 drops of water capacity per pound of refrigerant plus oil, so 10 lb of R-410A and 2.5 lb of POE needs 113 drops (Copeland AE11-1297).
- Anyone who opens the circuit to swap a drier must hold EPA 608 certification, Type II for high-pressure systems such as R-410A (40 CFR 82.161).
What does a filter drier do?
A filter drier does three jobs in one brazed shell: it adsorbs water, captures acid and strains out solids. In Sporlan’s words, moisture “is always present in refrigeration systems, especially with the use of hygroscopic polyolester (POE) lubricants,” and it drives acids, sludge, copper plating and corrosion.
Copeland’s AE11-1297 bulletin adds that POE oils are “extremely hygroscopic” and hydrolyze in the presence of water, creating acids. The solids matter too: Sporlan notes that metal chips and scale can plug capillary tubes and the inlet screen of a thermostatic expansion valve, which is why the drier sits just upstream of it.
What is inside a filter drier?
Inside is a molded core or packed beads of desiccant. Molecular sieve holds water, activated alumina holds acid, and some burnout cores add activated carbon. Danfoss lists its DCB core as 80% molecular sieve with 20% activated alumina, and its DMB core as 100% molecular sieve. Copeland caps its EK blend at 25% activated alumina behind a 20 micron outlet filter.
Ratings follow AHRI Standard 710. Water capacity is stated in drops, and 20 drops equal one gram. Danfoss gives a worked case: a DML 53 drier takes 8.5 kg (18.7 lb) of R134a from 1050 ppm of moisture down to 75 ppm at 24°C (75°F).
Liquid line, suction line or bi-flow filter drier: which goes where?
A liquid line filter drier goes between the condenser and the metering device, a suction line filter drier sits just ahead of the compressor for cleanup, and a heat pump needs a bi-flow drier because its liquid line runs both ways. Sporlan calls the liquid line the most effective location.
| Type | Where it goes | Main job | Maker data |
|---|---|---|---|
| Liquid line (one way) | Condenser outlet to metering device | Dry, capture acid, filter | Sporlan: never subject to reverse flow |
| Bi-flow (heat pump) | Liquid line of a reversing system | Same job in both flow directions | Sporlan HPC uses a check valve; Danfoss DMB flows outside to center either way |
| Suction line | Just ahead of the compressor | Cleanup after a compressor burnout | Sporlan: 3 psi permanent, 8 psi temporary (R-410A air conditioning) |
| Replaceable core shell | Liquid or suction line, larger systems | Swap cores without cutting pipe | Sporlan: mount horizontally so debris cannot drop into the outlet |
Sporlan says suction gas moves “about six times the velocity” of liquid, so suction driers need larger shells to hold pressure drop down. That is the drier in the cleanup kit after a compressor replacement.
Danfoss says a standard drier works in only one direction, so a system with a four-way reversing valve needs either two driers with check valves or one bi-flow drier. The Emerson BFK instructions (mirrored copy) warn that pressure drop rises when a liquid and vapor mix flows through it on single expansion valve heat pumps, so size up.
What are the symptoms of a clogged filter drier?
The classic sign of a clogged filter drier is a cold, sweating or frosted outlet. Danfoss says condensation “or even ice” at the outlet, with normal condensing temperature and no subcooler, most likely means the core is clogged with dirt.
A restriction starves the evaporator, so expect low suction pressure and high superheat. Our superheat and subcooling guide walks through those readings. A technician confirms it this way:
- Run the system until pressures settle.
- Read pressure at access ports before and after the drier; Danfoss says a gauge check “will show a correspondingly high pressure drop.”
- Compare against the maker rating: liquid line driers are rated at 1 psi at rated flow, so a much larger drop points to a loaded core.
- Replace the drier; Danfoss calls replacement “the only remedy.”
Correction
A guide ranking for this search attaches a 2 to 3 psi limit to the liquid line drier. In Sporlan’s bulletin, the 2 and 3 psi figures are suction line limits for permanent air conditioning installs, and suction driers are rated under ANSI/AHRI Standard 730. We found no maker document with a liquid line temperature drop threshold, so measure pressure instead.
When should you replace a filter drier?
Replace a filter drier every time the refrigerant circuit is opened, when the core is saturated or restricted, and after a compressor burnout. Danfoss puts the first rule plainly, and the Emerson instructions add that a very wet system may need the drier replaced “several times” to reach a safe moisture level.
On a moisture indicator, Danfoss says green is acceptable and yellow signals a problem. After a burnout, Sporlan says to measure pressure drop across a suction line drier during the first hour’s operation and replace it if the drop becomes excessive.
Worked sizing math
Copeland’s method sizes water capacity at 9 drops per pound of refrigerant, plus the same for the POE oil charge. Its example: (10 lb R-410A + 2.5 lb POE) × 9 = 113 drops. The same method applied to a heat pump with an 8 lb R-410A charge and 1.5 lb of oil gives (8 + 1.5) × 9 = 85.5, so pick a drier rated for at least 86 drops at the 50 ppm R-410A basis. Danfoss adds that a slightly larger drier has no real downside beyond length.
How is a filter drier installed correctly?
A filter drier is installed with the arrow pointing toward the metering device, brazed under a nitrogen purge with the shell kept cool, then pressure tested and evacuated.
- Recover the charge first; our refrigerant recovery guide covers the EPA levels.
- Keep the seal caps on until the moment of installation, as Emerson instructs, to keep moisture and dirt out.
- Match flow to the arrow on the label. Emerson says to locate it as close as possible to the expansion device inlet.
- Braze with dry nitrogen flowing, which Danfoss says prevents internal scale. Use a wet wrap and keep the flame off the shell, per the Danfoss DML installation guide and Sporlan; Emerson caps body temperature at 330°C (626°F).
- Pressure test, then pull a deep vacuum with an HVAC vacuum pump, often through the Schrader valve service ports.
- After run time, check the moisture indicator color, as Emerson recommends.
Long or reused refrigerant line sets raise the stakes, because any moisture left in the tubing ends up in the core.
Who may open the circuit, and what changes with A2L refrigerants?
Only an EPA 608 certified technician may open the circuit to change a filter drier. Under 40 CFR 82.161, anyone who could “violate the integrity of the refrigerant circuit” must pass an approved exam, and high-pressure appliances call for Type II. Our EPA 608 certification explainer covers the types.
Before opening, 40 CFR 82.156 sets evacuation levels. A high-pressure system under 200 pounds of charge goes to 0 inches of mercury with modern recovery equipment. A repair that is not “major” under 82.152, where the system will not be vented afterward, may stop at 0 psig. Major means removing a compressor, condenser, evaporator or auxiliary coil, or leaving more than four square inches of flow area open for over 15 minutes.
A2L refrigerants change part selection and flame handling. Danfoss approves DML connections below 25 mm for A2L refrigerants including R32 and R454B, and Sporlan says its Bulletin 40-10 driers are designed for A2L and A3 use. On A2L systems such as R-454B equipment, Copeland says never use a torch to remove a compressor, only tubing cutters. Follow the equipment maker’s instructions for drier joints.
How we researched this
Researched October 14, 2026. We read 15 documents, including two ranking competitor pages, and cite 9: Sporlan (Parker) Bulletin 40-10, three Danfoss documents, Copeland Application Engineering Bulletin AE11-1297 R7, Emerson’s ADK/BFK/FDB instructions, and 40 CFR 82.152, 82.156 and 82.161 from the eCFR. Maker figures are maker data, not independent tests. Bulletin 40-10 is cited from an archived copy because Parker blocks direct downloads.
Excluded: unsourced figures on ranking pages (compressor life gains, failure percentages), and retail prices, because no federal series covers drier replacement cost. Reddit was not used.
Frequently asked questions
Can you run an AC without a filter drier?
It will run, but nothing then catches moisture or debris. Sporlan says moisture is always present in systems using POE oil and drives acids, sludge and corrosion, while solids can plug a TXV screen or capillary tube. Danfoss treats a new drier as part of every job that opens the system.
How much does it cost to replace a filter drier?
No federal source publishes a price, so we do not quote one. Most of the cost is labor: recovering the charge to the 40 CFR 82.156 levels, brazing, pressure testing, evacuating and recharging, all by an EPA 608 certified technician.
Which way does the arrow on a filter drier point?
The arrow shows refrigerant flow, so it points away from the condenser and toward the metering device. Emerson says flow must match the label arrow on its one-way ADK and FDB driers. A bi-flow drier such as the BFK has no fixed direction because the heat pump reverses flow.
Is it filter drier or filter dryer?
Both spellings mean the same part. Sporlan, Danfoss and Copeland all spell it drier, as does the ASHRAE Standard 63 test method, “Methods of Testing Liquid Line Refrigerant Driers.” Searchers type both, but the catalogs and installation guides a technician works from say drier.
Where is the filter drier located on a central AC?
On the liquid line, the smaller of the two copper lines, between the condenser outlet and the metering device. Emerson recommends placing it as close as possible to the expansion device inlet, so depending on the equipment it may sit near the indoor coil or inside the outdoor unit.
How long can a suction line filter drier stay in the system?
Sporlan says a suction line drier is generally left in the line after cleanup, with the cores in replaceable models swapped for filter elements to cut pressure drop. Its limits for R-410A air conditioning are 3 psi drop for a permanent install and 8 psi for a temporary cleanup install.
Sources
- Sporlan Division of Parker Hannifin. “Bulletin 40-10: Catch-All Liquid and Suction Line Filter-Driers (January 2022), archived copy.” https://web.archive.org/web/2025/http://www.parker.com/Literature/Sporlan/Sporlan%20pdf%20files/Sporlan%20pdf%20040/40-10%20Catch-All%20Filter-Driers.pdf. Accessed October 2026.
- Danfoss. “Filter driers and sight glasses.” https://www.danfoss.com/en/service-and-support/case-stories/dcs/filter-driers-and-sight-glasses/. Accessed October 2026.
- Danfoss. “Refrigeration filter drier (DMB/DCB product page).” https://www.danfoss.com/en-us/products/dcs/filter-driers-and-strainers/filter-driers/. Accessed October 2026.
- Danfoss. “ELIMINATOR Hermetic filter drier Type DML/DMLE/DCL/DCLE installation guide.” https://assets.danfoss.com/documents/latest/203629/AN165086432065en-000601.pdf. Accessed October 2026.
- Copeland. “Application Engineering Bulletin AE11-1297 R7: Liquid Line Filter Driers (October 2024).” https://webapps.copeland.com/online-product-information/Publication/LaunchPDF?Index=AEB&PDF=1297. Accessed October 2026.
- Emerson Climate Technologies. “Operating instructions, Filter Drier Series ADK/BFK/FDB (R09, April 2020), mirrored copy.” https://www.c-o-k.ru/library/instructions/emerson/zapchasti-komplektuyuschie/102091.pdf. Accessed October 2026.
- eCFR. “40 CFR 82.161 Technician certification.” https://www.ecfr.gov/current/title-40/chapter-I/subchapter-C/part-82/subpart-F/section-82.161. Accessed October 2026.
- eCFR. “40 CFR 82.156 Proper evacuation of refrigerant from appliances.” https://www.ecfr.gov/current/title-40/chapter-I/subchapter-C/part-82/subpart-F/section-82.156. Accessed October 2026.
- eCFR. “40 CFR 82.152 Definitions.” https://www.ecfr.gov/current/title-40/chapter-I/subchapter-C/part-82/subpart-F/section-82.152. Accessed October 2026.
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