Filter-dryers and Capillary Tubes


Replacement filter-dryer


Filter-dryers are placed at the outlet of the condenser in household refrigerators and contain mesh screens to trap contaminants and chemicals to absorb moisture. This provides protection to the capillary tube which can become clogged and block the flow of liquid refrigerant to the evaporator. A completely blocked capillary tube will stop all refrigerant from reaching the evaporator and no cooling takes place.

A clogged capillary tube is difficult to diagnose since it seems the unit is low on refrigerant (the evaporator doesn’t receive refrigerant, but not because it has leaked out). This is one situation where piercing-valves and manifold gauges are necessary to be certain. A system with a clogged cap tube and a good compressor will pull the low-side suction pressure down into a vacuum as low as 20 inches of hg. The condenser will be cold since it contains liquid refrigerant under high pressure. If the high-side pressure is low and the low-side is in a vacuum, the problem is likely a lack of refrigerant rather than a clogged capillary tube.

The filter-dryers installed to protect the capillary tube can also clog and the symptoms look the same as a clogged capillary tube. If a filter-dryer is only partially clogged and creates a pressure drop it will be coated with frost. A frosted dryer or frost on the cap tube at the outlet of the dryer indicates a partially clogged dryer that needs to be replaced. Dryers are cheap, but the economics of hiring a refrigeration tech to recover the refrigerant, replace the dryer, and then evacuate and recharge the system will depend on the age and cost of the system and type of refrigerant. R12 systems are likely better retired.

Capillary tubes usually clog in the first few inches after the dryer unless the system is contaminated with moisture. Moisture will almost always freeze and form an ice-plug at the inlet to the evaporator. This happens if the system is opened, moist air allowed to enter the piping, and a complete evacuation with a quality vacuum-pump is not performed prior to recharging.

Cap tubes can be replaced, but it is not an easy task. Almost all are attached to the suction line for much of their length. Their internal bore and length are part of the refrigerator design and cannot be replaced with just any cap tube one might have. The size depends on the type of refrigerant and capacity of the compressor.

In my foolish youth, I used to replace clogged cap tubes on almost new refrigerators by removing the evaporator, suction line, and cap tube back to the compressor area (as long as they were not buried in the foam insulation) and replacing the whole thing with a similar evaporator/suction line/ cap tube assembly from a scrapped refrigerator. The refrigerator that I am using now received this treatment, a new compressor, and a charge of R-409a over eight years ago.

In the past year I have seen three Frigidaire side-by-side refrigerators in which the capillary tube had not been brazed into the filter-dryer during manufacture. Thus they were sold (and returned to the retailer) without refrigerant. The replacement of the filter-dryer, evacuation, and charging with R-134a was worth it since they retailed for almost two thousand dollars each. Two other new Frigidaire units that I saw had broken cap tubes where they entered the filter-dryer. This likely happened in shipment (its a long way to China) due to the crappy placement of filter-dryers on Frigidaire side-by-sides.


Filed under appliance, diagnose and repair, refrigerator repair

25 responses to “Filter-dryers and Capillary Tubes

  1. Roge

    Thanks for the info. I am working on a refrigerator; the area where the capillary tube enters the evaporator has ice. The evap has no frost. The condenser is room temperature except for approx 3′ from the compressor. I think maybe the capillary tube has moisture. Would that be correct?

    • fridgeman

      Test for an ice-blockage by placing a warm cloth around the cap-tube where it enters the evaporator. If the evaporator begins to form frost, moisture freezing inside the sealed system is likely. If there is no change, suspect a shortage of refrigerant or if an older unit a worn compressor valve.

      • Roge

        Thank you much. Turned out that the system had restrictions so I emptied the system and replaced the dryer (then re-gas). It is working fine now.

    • Barbara

      I agree!! Great site!!
      Roge…. Our repairman says he can’t access the dryers and capillaries. Our GE monegram built in needs to be replaced??? I don’t think so. What do I tell these people? Does GE really make appliances that can’t be repaired? Thanks!

      • fridgeman

        Most dryers are accessible and can be replaced but many manufacturers now route the cap tube and suction line beneath the skin of the chassis. They have no reason to want you to be able to repair the unit since they are in the refrigerator selling business.

  2. CJ

    I have a kenmore side by side (model 10657362700) that I purchase in 2007. The refrigerator was in a house unplugged for about two years (still has blue tape on unit; never used). I plugged the unit up about 3 months ago and it worked. Soon after we unplugged the unit. Now, the refrigerator does not work (does not get cold on both sides, only lights and water works). I have been told that the cap tubes are clogged. Is that possible since we never used the unit or did the down time could have caused this problem? Could it be something else? As you can see I need help. Thank you for your time.


    • fridgeman

      I doubt if the down time caused the problem. Have you verified that the compressor is starting and running? I have seen many more almost new refrigerators with defective compressor start circuits than with clogged filter dryers.

  3. Just wanted to say that your blog is superb! I have been roaming around the net for a few hours looking for information and possible answers to my fridge problem, and my hunch has been confirmed as probably correct after reading several of your posts.

    Rather a treat to have such detailed information delivered in such a well-written way. Thanks!

  4. Dionysius

    Your website is excellent. Most professional and without parallel. This site will gain a lot of interaction and you may consider an e-Book with a compilation of the information at a future time.

    Keep up the excellent work and many thanks.

  5. Davids

    Hi i have a foster double fridge is take 350g of gas. the capilliary tube has complete frost its whole length. but no frost on filter drier but there is a temp difference across drier. evaporater is room temp not getting cold at all. thanks for you time

  6. nilo

    In reference to captubes and the headaches they present.

    I am doing a warranty job for a company that sold a preptable to a local pizza shop. The compressor locked up after 6 months of operation (made in Brazil). The company that is honoring the warranty wants the sealed system flushed and the captube replaced. I said OK too quickly.

    NOW THE PROBLEM. The evaporator is on the end of the preptable cabinet and up underneath the air circulation plenum for the toppings. It is impossible to get to the evaporator inlet of the captube and desolder it without further teardown of the cabinet . I find that the whole top of this preptable will have to be lifted off to expose the evaporator from the top in order to do the captube replacement. It appears that the evaporator was installed at the factory from the top before the preptable was given its air circulation plenum. GREAT!

    I am waiting for the company that made this preptable to reply on being informed that there will be a lot more labor time in this job.

    So I am just wondering out loud: Knowing that such things as this preptable are assembled the cheapest way possible, would it be unreasonable for the designers to take account that there should be an access panel located on the cabinet so that the evaporator could be serviced FROM OUTSIDE THE END OF THE CABINET?

    I don’t think they really know or care what the field servicemen encounter in working on their incompetent designs.

    The more I work on some manufacturer’s equipment, the more I want to avoid such poor designs and tell my customers that they need to be more prudent in buying equipment. It like having to drop your gas tank from your car before you can replace the fuel pump and sending unit. It is incompentent design.

    But you never run down the customer’s choice in equipment. The cheapest designed equipment is not always the most cost effective. Design and accessibility have a lot to do with saving money down the road. If this preptable had been out of warranty (most of which are not worth the paper they are written on; one year!! give me a break!), they would be paying a lot to fix this. As it stands, this pizza shop won’t be paying for this repair this time, but they bought two (2) of them!! LOOK OUT!

  7. Ed

    So after reading a milion blogs, I think I am ready to accept the service man’s diagnosis that I need a new refrigerator. My refrigerator/freezer is working fine..or so we thought But, the leak we did not know we had ruined my floor. When we pulled out the fridge for renovation, we found that there was exterior condensation on the copper tubing at the back of freezer (capillary tube) which creates ice that eventually drops off of the tubing. This happens regularly and every time the ice drops, it creates a puddle of water on the floor. What do you think?

  8. Kjell

    Hi, I have a question about the way you explain capillary tubes. I work aboard a ship, and a part of the job is maintaining the reefer systems.
    The capillary tube is connected to the expansion valve, inside the tube is a liquid that expands with heat. At a certain temperature the liquid inside the capillary tube will “push” open the expansion valve, thus letting refrigerant trough to the evaporator.
    In my experience this tube cannot be clogged, the only thing i heard gone wrong with this is that the membrane between the capillary tube and the expansion valve has started leaking.
    Does the capillary tube work differently on domestic refrigerators?

    • fridgeman

      Most domestic refrigerators do not use expansion valves to control the flow of refrigerant to the evaporator. The small diameter of the capillary tube employed meters refrigerant flow and is sized to maintain high-side pressure. The small bores of these tubes are more easily clogged than systems using expansion valves to control refrigerant flow.

  9. Hi, what would you looked at ones your low side and high side a both in vacuum. Low side in deep vacuum. Thanks

  10. Hi;
    I have a household LG Fridge with a bottom freezer. When it was not getting cold at all in the top and only slightly cold in the bottom freezer, I called a repair guy. He came, took the back panel off the fridge bottom. Touched the compressor and coil with his bare hands and said all the freon was gone, unplugged it, and told me to buy a new fridge. Of course, I was not satisfied with this. The fridge is only 5 years old (R134), it was pricey, and no apparent damage or punctures inside. So I took off the cover in the back of the freezer and and I assume the coil is what you call the evaporator. I plugged back in and checked it after a few minutes and low and behold there was frost on what I am guessing is the capillary tube leading up to it, and the evaporator (or what I assume is) was cold for a few inches in. Does this mean there is freon in it and it was misdiagnosed? Is likely a blocked capillary?

    • fridgeman

      frost on the cap tube could indicate a restriction especially if it occurs before the cap tube enters the evaporator coil. The evapoartor only being cold for a few inches and not frosted along most of its length suggests a lack of freon TO THE EVAPORATOR. That doesn’t mean that the system has developed a leak. The tech probably felt the condenser coil for heat and decided the system was empty. If the cap tube is frosted at any point other than where it enters the evaporator. it is partially restricted.

  11. Christina

    Great information! I have a 13 yr old Kenmore with a bottom freezer and over the last week the freezer has been warming up (watching temp go from -8 c to -3 c. I know nothing about fridges but do know that early in its life, it had two replaacement compressors and a fan under warranty (other owners). Fan and compressor run but air is not cool (in my esitmation). Access to innards seems like quite a process. Is this a clear case of paying for servicing and what is the likely outcome?

    • fridgeman

      There are many conditions that could cause a gradual rise in freezer temp. If you know nothing about refrigerators, a service call to determine problem might be the right choice.

  12. Christina

    I was told there is no Freon because the fins are not covered in frost – they are bone dry. The freezer is now almost at 0 c after two days, as the problem seems to worsen. I just paid to be told that the fridge is not fixable…
    Service records from previous home owners shows at least 1300 dollars in repairs… After reading your material, I am not confident that a “no Freon” with just a visual inspection is the unequivocal answer? Unless, a previous repair somehow damaged the lines?

  13. Joseph

    Great blog — I have a Frigidaire side by side we bought it in 2011 and it was manufactured in 2009. I didn’t realize it was that old when they delivered it (from a national retailer) but that is another story. It has the digital temp setting and display and a few days ago the freezer was 10F and its set for 0F. After cleaning the condenser and fans and making sure the fans are working (it wasn’t that dirty) I defrosted the evaporator which was iced at the cap tube and 2-3 inches in. It seems that the evap is cooling but only the first 5% of the evap is below freezing. Repairman said the Fridge will be a continual issue as he thinks the compressor is releasing trash into the system. Which has clogged the evaporator. Does this seem right? the size difference doesn’t seem likely the evaporator is clogged, maybe the cap tube or filter. Maybe he was just dumming it down. So now I am fighting with Frigidaire on the fact the problem likely existed while it was under warranty although the problem wasn’t uncovered until it went out of warranty.

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