Air Conditioning & Heat Pump Refrigerant Drier / Filter Use & Installation
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What is that grey canister you see at an air conditioning component: why are driers and filters installed on refrigeration equipment?
When is a refrigerant gas drier usually installed
Where should the refrigerant drier be installed on refrigeration equipment
Special refrigerant drier/filter for use when a compressor motor has been replaced
Diagnosing a saturated or dirt-clogged refrigerant drier canister
How to fix air conditioning or refrigerator refrigerant gas leaks

This article discusses when, where, how and why refrigerant driers are installed on refrigeration, air conditioning and cooling systems.

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Installing a Refrigerant Dryer / Filter Unit on the Air Conditioning or Heat Pump Refrigerant Line

Refrigerant dryer device (C) Daniel Friedman

Our photo at page top shows the typical location of a refrigerant dryer canister at the compressor/condenser component of a split system air conditioning system.

If your air conditioning or heat pump system has lost its cooling capacity or won't start see REPAIR GUIDE for AIR CONDITIONERS. See How to determine the cooling capacity of air conditioning equipment if the system seems to be working but is inadequate to cool your building. Also see REFRIGERANTS, see PRESSURE READINGS, COMPRESSOR, and A/C REFRIGERANT LEAK DETECTION for more details.and see REFRIGERANT PIPING & DISTANCES. Contact us to suggest text changes and additions and, if you wish, to receive online listing and credit for that contribution.

Once an air conditioner or heat pump system refrigerant leak has been repaired, it will be necessary to flush the refrigerant piping system (usually using nitrogen), pull a new vacuum on the system, and then re-charge the system with the proper type and quantity of refrigerant.

Our photo at left shows that a Catch-All™ C-163_S refrigerant dryer and filter has been installed on the high pressure refrigerant line leaving the outdoor compressor/condenser unit. This is where we usually see this device installed. Notice that the refrigerant dryer, which removes un-wanted moisture from the refrigeration system, is labeled with the types of refrigerant with which it is designed to be used.

Most driers are designed to be soldered in place, as is the unit shown at left. Some driers may permit connection using flare fittings - a connection we consider less secure and more leak prone.

When a refrigeration system is or has been "open" - has been emptied of refrigerant for re-charging, for example, the last repair step before re-charging the repaired air conditioning or heat pump system with refrigerant is to install a filter/drier such as shown in our photo at left.

The purpose of a refrigerant drier is to absorb (and thus remove) moisture in the refrigeration system. The effects of moisture on refrigeration systems are detailed at REFRIGERANT LEAK DETECTION but in sum we can say that moisture in the system can prevent proper operation and can even completely stop the system from working at all, even causing costly damage.

We also find a drier installed on refrigeration systems that have been serviced for a refrigeration leak, especially a low-side piping leak, because of the increased chance that the system has been contaminated by moisture and perhaps dirt. In fact if the system was open and badly contaminated the HVAC technician may install a drier right after the repair and may install a new or second drier on the same system a few months later.

While some technicians always install a filter/drier on the refrigerant system, even at original installation, more often when we see a refrigerant drier canister on a system (usually at the compressor/condenser unit) we assume that the system has undergone some service or repair as that's most often when the device is added.

Refrigerant Filter Installation Positions

Where is the Drier Usually Located on an Air Conditioning, Heat Pump, or other Refrigeration System?

The drier is installed at the coolest location on the system, on the liquid line, outside of the refrigerated space, and ahead of any refrigerant metering devices like thermostatic expansion valves or capillary tubes.

In our photo (left) you can see that the drier has been installed outdoors, at the point where the high side liquid refrigerant line is exiting the compressor/condenser unit.

In our photo below left you'll see a filter/drier installed in two locations on the air conditioning system compressor/condenser.

Refrigerant Debris Filtering

Refrigerant Driers not only remove moisture, they also are intended to filter debris from the refrigerant piping system.

Filtering the refrigerant liquid leaving the compressor/condenser protects the Thermal Expansion Valve or capillary tube from clogging. In at least some refrigerant drier/filter models, the presence of the strainer means that the drier/strainer device has to be installed in a particular direction such that particles of the desiccant do not break free and travel through the refrigerant piping system.

In our air conditioner compressor / condenser unit photo (left) you may notice that two driers are installed, one on the low side and one on the high side. The suggestion is that repair work has been done on this system.

Why is a filter-dryer critical on an air conditioner or refrigeration system that has been worked-on?

Water anywhere inside the refrigerant handling system (tubing, compressor, condenser, or refrigerant metering cap tube or thermostatic expansion valve) freezes, making the system inoperative. The inside of any refrigeration system must be pure refrigerant: no air, no dirt, no water, and no mix of various refrigerant gases other than a single gas for which the system is designed.

Watch out: above we mentioned that on a badly contaminated refrigeration system the technician may install a new or a second drier a few months after the original repair/service. If a drier has become saturated in the course of doing its job (of removing moisture from the refrigerant system), it begins to restrict the flow of refrigerant through the system. This refrigerant flow restriction will cause pressure changes indicated by a temperature difference on either side of the drier - that's one way you could quickly test for a clogged refrigerant drier.

Watch out: if you change the size of the drier that you have installed on a refrigeration system that does not use a refrigerant receiver (as is the case with most residential appliances and air conditioners/heat pumps, you will have to compensate in the charge used in the system (if it is a "critically-charged" or precise charge system as we've discussed here). For example if you install a larger drier than was previously in place you'd need more refrigerant charge in order to assure that the frost line will still extend to the end of the evaporator.

Special Burnout Filters Used after a Compressor Motor Replacement

A "burnout drier" is a special drier installed on refrigeration systems when a compressor motor has burned out and the compressor is changed out. In this case we have to clean the acid and lacquer out of the refrigeration system. (Using Karene-R11).

The system is washed out and then the burnout drier is put in temporarily in the low side or return refrigerant line, replaced one or more times as needed, until the system is cleaned. Therefore you might not normally see a drier in this position on a system except during that repair process.

More details about what moisture and contaminants do to a refrigeration system are discussed at REFRIGERANT LEAK DETECTION

What is the Life Expectancy of a Refrigerant Drier Installed on an Air Conditioner or Heat Pump or Refrigerator/Freezer?

Ordinarily a drier should last the life of the equipment, given no leaks or problems with the system that require that the refrigerant piping be cut. (The piping will be cut and the system opened, for example, if a cooling coil or condensing coil has to be replaced.)

Frequently Asked Questions (FAQs) about refrigerant driers

Question / Comment: Failure to install a burnout filter/dryer may have led to early failure of the replacement unit

Afet a contractor replaced a failed compressor ) that failed via acid burnout) he left in the 16 year old suction line filer,,,he never put in a burnout filter at all....the compressor failed in just 13 months they normally last 18 plus years. I think he should refund the 42,000 he charged me what do you think.

When I asked the contractor to explan his substandard work he said I can't prove 100% that the dirty gunked up suction line filter caused the 3 1/2 ton Copland compressor to fail ,,,what a joke. - Tom Morris

Reply:

Tom, we agree with you. Good practice would have been to install a burnout dryer-filter on the system and perhaps, depending on how dirty the system was from the first burnout, to return and swap in a second filter unit after a period of time. The cost to the tech to come back to make that second change is not trivial however, and both owner and tech are tempted to skip it. The risk is clogging of the thermal expansion valve or other parts in the future, leading to still more repairs.

But I wouldn't assume that the prime or only cause of failure of the replacement compressor was just due to the dryer omission. A tech who doesn't know about the importance of all of the steps in replacing a burned out A/C or heat pump compressor may not have known other important steps to take.

Question: Where does the refrigerant drier/filter go?

Dan,
Regarding installation of a filter/dryer; the filters I have seen on HVAC parts sites are for installation on the suction side. When I installed an AC in my house in '88, I installed a filter/dryer in the liquid line, near the coil as recommended at the time. It seems to me that it makes more sense to filter the liquid entering the TXV than to filter the gas entering the compressor. What am I missing? I purchased the compressor on eBay. It turns out that it was exactly the P/N specified in the parts list for the equipment. The gaspack contained what I assume was an earlier equivalent part. - Doug

Reply:

Doug we see filter dryers installed at both sides of the compressor. It depends ... if a system is thought to be contaminated there are advantages of having a filter at both ends of the compressor motor, and it certainly doesn't hurt.

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REFRIGERANTS
  GAUGE, REFRIGERATION PRESSURE TEST
  REFRIGERANT CHARGING PROCEDURE
  REFRIGERANT DRIERS & FILTERS
  REFRIGERANT LEAK DETECTION
  REFRIGERANT LEAK REPAIR
  REFRIGERANT METERING DEVICES TEVs
  REFRIGERANT METERING CAPILLARY TUBES
  REFRIGERANT PIPING & DISTANCES
  REFRIGERANT PRESSURE READINGS

Thanks to to Guy Benfante, Chesapeake, VA 8/26/07 for the photograph of an ice-blocked air conditioning system evaporator coil and for his suggestion that we provide an air conditioning system troubleshooting FAQ.
Thanks to Mark Cramer, Tampa Florida, for assistance in technical review of the "Critical Defects" section and for the photograph of the deteriorating gray Owens Corning flex duct in a hot attic. Mr. Cramer is a Florida home inspector and home inspection educator.
Carson, Dunlop & Associates Ltd., 120 Carlton Street Suite 407, Toronto ON M5A 4K2. (416) 964-9415 1-800-268-7070 info@carsondunlop.com. Thanks to Alan Carson and Bob Dunlop, for permission to use illustrations from their publication, The Illustrated Home which illustrates construction details and building components. Carson Dunlop provides home inspection education including the ASHI-adopted Home Inspection Training Program (home study course), publications such as the Home Reference Book, report writing materials including the Horizon report writer, and home inspection services. Alan Carson is a past president of ASHI, the American Society of Home Inspectors.
Carson Dunlop, Associates, Toronto, have provided us with (and we recommend) Carson Dunlop Weldon & Associates' Technical Reference Guide to manufacturer's model and serial number information for heating and cooling equipment ($69.00 U.S.).
Thanks to reader Don Jackson for HVAC refrigerant leak soldering repair tips (Aug-Sept 2008).
Wikipedia provided background information about the definition of HEPA and airborne particle interception.
Modern Refrigeration and Air Conditioning, A. D. Althouse, C.H. Turnquist, A. Bracciano, Goodheart-Willcox Co., 1982
Principles of Refrigeration, R. Warren Marsh, C. Thomas Olivo, Delmar Publishers, 1979
"Air Conditioning & Refrigeration I & II", BOCES Education, Warren Hilliard (instructor), Poughkeepsie, New York, May - July 1982, [classroom notes from air conditioning and refrigeration maintenance and repair course attended by the website author]
Refrigeration and Air Conditioning Technology, 5th Ed., William C. Whitman, William M. Johnson, John Tomczyk, Cengage Learning, 2005, ISBN 1401837654, 9781401837655 1324 pages
Carson Dunlop, Associates, Toronto, have provided us with (and we recommend) Carson Dunlop Weldon & Associates' Technical Reference Guide to manufacturer's model and serial number information for heating and cooling equipment ($69.00 U.S.).
Air Conditioning Inspection, Diagnosis, Repair, Efficiency all the basics for home owners, inspectors, new repairmen

Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair

Our recommended books about building & mechanical systems design, inspection, problem diagnosis, and repair, and about indoor environment and IAQ testing, diagnosis, and cleanup are at the InspectAPedia Bookstore. Also see our Book Reviews - InspectAPedia.
Complete List of Air Conditioning & Heat Pump Design, Inspection, Repair Books at the InspectAPedia Bookstore.

The Home Reference Book - the Encyclopedia of Homes, Carson Dunlop & Associates, Toronto, Ontario, 2010, $69.00 U.S., is available from Carson Dunlop. The Home Reference Book is a bound volume of more than 450 illustrated pages that assist home inspectors and home owners in the inspection and detection of problems on buildings. The text is intended as a reference guide to help building owners operate and maintain their home effectively. InspectAPedia.com ^® author/editor Daniel Friedman is a contributing author. Field inspection worksheets are included at the back of the volume.

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Installing a Refrigerant Dryer / Filter Unit on the Air Conditioning or Heat Pump Refrigerant Line

Refrigerant Filter Installation Positions

Where is the Drier Usually Located on an Air Conditioning, Heat Pump, or other Refrigeration System?

Refrigerant Debris Filtering

Why is a filter-dryer critical on an air conditioner or refrigeration system that has been worked-on?

Special Burnout Filters Used after a Compressor Motor Replacement

What is the Life Expectancy of a Refrigerant Drier Installed on an Air Conditioner or Heat Pump or Refrigerator/Freezer?

Frequently Asked Questions (FAQs) about refrigerant driers

Question / Comment: Failure to install a burnout filter/dryer may have led to early failure of the replacement unit

Reply:

Question: Where does the refrigerant drier/filter go?

Reply:

Questions & Answers regarding this article

Ask a Question or Search InspectAPedia

Technical Reviewers & References

Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair