Refrigerant filter drier canisters:
This article discusses when, where, how and why refrigerant driers are installed on refrigeration, air conditioning and cooling systems. 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.
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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.
Article discussion topics: 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
Carson Dunlop Associates' sketch illustrates where the filter/dryer is most often found at air conditioning or heat pump equipment: on the liquid refrigerant line, in one or more of these locations:
Most HVACR refrigerant filter-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.
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.
A typical indoor refrigerant filter/drier location is shown in our sketch at left: see the blue canister with red arrow showing refrigerant direction flow in Carrier's sketch at left (edited)).
Watch out: UNIT DAMAGE HAZARD Failure to follow this caution may result in equipment damage or improper operation. Installation of filter drier in liquid line is required.
Below our photo illustrates the installation of a refrigerant filter/drier at the A-coil - you can see the horizontal drier canister to the right of (and protecting) the tan-colored Thermostatic Expansion Valve (TEV).
Source: PURONR (R--410A) REFRIGERANT QUICK REFERENCE GUIDE-
Watch out: be sure to check the installation instructions for your specific HVAC equipment before installing a filter-drier. And be sure that you are installing the proper type of filter-drier, intended for use on a suction line or on a liquid refrigerant line.
For example, some newer equipment such as the 24 ANA Infinity™ Series Air Conditioners with Puron® Refrigerant, include instructions that state:
Our photograph illustrates the installation of filter driers on both the liquid refrigerant line and the gas "suction line" at an outdoor compressor-condenser unit.
Watch out: the filter drier types are not identical - the proper filter/drier type must be matched to its location and use on liquid versus gas refrigerant piping.
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 can observe that two refrigerant filter-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, possibly a compressor replacement.
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.
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 "suction 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.
The burnout filter drier is a special unit able to remove acids and contaminants that were created when the old compressor burned out. These driers also usually provide the ability to compare pressures across the device. If the filter/drier is clogging and thus causes a reduced pressure on the suction side, the compression ratio in the compressor increases, compressor efficiency drops, and in extreme cases the equipment could be damaged.
Watch out: experts warn that the suction line dryer is not only important, but that it must be sized properly to match the system's design flow rate of refrigerant.
More details about what moisture and contaminants do to a refrigeration system are discussed at REFRIGERANT LEAK DETECTION
Martin Chan said:
Hi! I was wondering how long is the life expectancy of the dryer filter? Once fixed, how do we know when to change a new one ? Are there any reasons for changing a drier filter ? Could I run a VRV system without the use of a drier filter ? What is the difference between installing a drier filter and not installing, for a VRV system ?
Martin I have several different answers to the question of refrigeration system filter-drier life:
A filter drier that is installed as good practice or precaution on a healthy HVACR system is left in place often for many years, even the life of the equipment.
A filter drier that was installed (usually two of them) following replacement of a burned-out compressor is often changed after a year, on the theory that it may have collected a fair amount of crud that ought to be removed to avoid risking blocking refrigerant flow. After that swapout the new filters are left in place indefinitely unless the technician finds a reason to do otherwise.
After those standard cases, on occasion a refrigerant filter drier MIGHT be removed and replaced if tests on the system showed that it is clogging.
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.)
Watch out: some filter driers installed on refrigerant piping have special short-term intended uses such as during new equipment installation or when used as a compressor burnout filter drier. E.g. Carrier's new equipment installation instructions state
Do not leave Puron suction line filter driers in line longer than 72 hours. 
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After 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 explain 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
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.
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
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.
(Aug 23, 2012) Susan said:
I had a new condensing unit put in. Does the installer need to come out after a month and put in a new dryer? Is it a suction or line dryer?
IF the old compressor burned up it's good practice to change out that filter drier as you suggest, though often the tech may leave the burnout filter drier in place for a longer interval before changing it. It depends on the type of dryer and where it was installed.
Watch out: Do not leave Puron suction line filter driers in line longer than 72 hours. 
(Mar 23, 2013) Zamree said:
Installation vertical orientation of liquid line filter drier for vrv/vrf or package compare to horrizontal posiotion - identify compressor pressure at starting too loading,create amp increase and long run compressor head temperature high and some case compressor easily burn out. This may come to critical if the field piping >30m, too many elevation(more then 10). System pressure unstable.
I'm so sorry but I don't understand your question. Sounds like you need an HVAC refrigeration engineer.
(May 12, 2014) Bob Gorman said:
Having installed External filter dryer. will they lose the refrigerant during installation and will have to be replaced?
Bob, filter-drier canisters do not lose refrigerant and are replaced as per discussed in the article above. If the HVACR technician follows good procedure while connecting her test equipment, gauges, charging cylinder etc. to the system refrigerant is not "lost" in the procedure such that adding refrigerant would be needed.
(June 2, 2014) Dave said:
I have a rheum heat pump installed new in 09 was fine till last year. Unit started making a whistle noise only on ac start up and shutdown not heat mode. Had 410a charge checked and about a pound was added. Noise was now less but he came back and added a little more 410a --- no change in noise.
Then ran heat pump a few months later and it shutdown on high pressure---suspect too much 410a ? Came back and let some out using the gauge set. Runs on heat pump now and ac but still make noise. Unit is in a condo / coil & or evaporator gas noise surging in line till it equalizes ? Very annoying at night. Did not do this for the first 3 years any ideas ? He doesn't know what to do & either do I.
Take a look at
and let me know if that helps.
(June 9, 2014) Grace said:
What happens if your compressor may need to be replaced due to liquid line dryer being found in the hot gas line? Can the compressor be saved? Thank you!
A Suction Line filter drier is installed to protect the compressor against damage and its installation is good practice. After a compressor burnout, because there is extra risk of contaminants in the refrigeration piping system, a special burnout filter dryer, capable of filtering out acids, is installed to protect the new copressor.
If we omit the burnout filter/dryer the risk is that we contaminate, damage, or reduce the life of the new compressor.
At this point of discovery of the error you cite, the right move is to install the proper filter dryer. If the system is working normally that's the best we can do, though you might discuss a dealer-supported extended warranty if the installer accepts responsibilty for the original error.
6/17/2014 edmund magras said:
A company installed a dry filter backward. It went un-noticed for about a year before it was replaced should I be concerned
The backwards drier itself won't cause damage to your system, but it may not have been filtering properly, leaving a risk of debris-clogging of the refrigerant metering device or other components. If those had clogged you'd know it because the system would not be working properly
Therefore my OPINION is that if the drier is now installed properly you're ok.
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