heat pump, Air conditioning coil ice or icing and freezing
is usually caused by a lack of refrigerant,
I get lots and lots of inquiries about air conditioners and heat pumps icing up the indoor coils and the large line to the unit in the Air Conditioning or Cooling mode.
due to a refrigerant leak or leaking
This is usually caused by a lack of refrigerant in the system due to a chronic leak. The reason that the coils form ice is that when the system is short on charge part of the coil runs very cold and ice starts to grow. Once the ice starts to grow it is in insulator and keeps on growing until the coil and the refrigerant lines are one block of ice. If the coil is very dirty then the ice will form out to the outside unit (cooling mode) very quickly.
The solution is to clean the coil or replace it (see below). A good cleaner is Acti-Klean by Virginia-KMP that works with the condensate water and doesn't require rinsing.
If this happens continuing to run the equipment will damage the compressor and not provide any cooling. If this was caused by running the system on a cold night, the best way to remove the ice is to leave the indoor fan on and let the ice melt (expect a mess).
To modify a system to operate in cold weather or if you like the house really cold like below 70 degrees you must add the following to your unit which you should have any way. Low pressure cut out CO=40psi and CI=80psi, anti restart timer 3-5 minuites, High pressure cut out manual reset, crank-case heater if a recipricating compressor, expansion valve AND sight glass (see below), head pressure controller if you are going to operate the system when it is cold outside. If you make all these modifications then you can run your system continuously with out hurting anything. note: no ice will form on the coil and you will have to make sure the system is properly charged. But if you want the house to be a "meat locker" because you sleep durning the day or have health problems then add the above items and "freeze your self out". A larger coil (see below) will make a huge difference too.
If you want to stop the system from freezing add the components listed above. If you need the system to continue to cool when the outside temperature is too cold for normal operation you will need a head pressure controler.
Refrigerant leaks will not go away and there is nothing that you can add to your system that will stop it. The only cure is to repair the leak. Usually when there is a refrigerant leak the oil that is mixed with the refrigerant will collect around the leak and attract dirt. Look for these stains and chances are good that is where the leak is (there can be more than one). We have seen many cases where a service company will keep adding refrigerant 22 (Freon) to a leaking system and claim that they cannot find the leak, but when the covers are removed the oil stains tell other wise.
Other things that will cause or aggravate ice are clogged filters, bad fan motors, to many closed vents, dirty filters (never been changed), running the system when it is "too cold outside" (below 65 degrees F) with out modifying the system for cold weather operation, clogged capillaries or bad expansion valves (I will address that in another page one day). Someone recently wrote me complaining that their unit ices up when it rains although they blamed "humidity" the real cause was that the head pressure would drop to the point where the indoor coil would ice up. Do not discount the possibility that the outdoor unit was replaced by one that is larger without changing the indoor coil to a larger capacity. We ran into a situation like this where factory representatives from Carrier had looked at the system and just added refrigerant because they never bothered to check the size of the indoor coil. There are supposed know what they are doing (another case of "take away the name").
We have seen an epidemic of clogged capillaries on Rheem/Ruud units on the indoor coil. The only fix is to replace the coil with one that has an expansion valve and watch the system work better than when it was new.
We recently worked on a Rheem/Ruud unit that had a bad compressor and after replacing the compressor we found a bad reversing valve (hissing real bad with high suction pressure). We replaced the reversing valve only to find the the metering orifice is the wrong size or clogged inside (air conditioning mode). The system is running about 40 psi suction pressure which will ruin the compressor and reversing valve. The reason that we know this is we put a liquid line sight glass on the system and the sight glass is full but the indoor coil is freezing up. The hard part is going to be explaining to the home owner that this has been the cause of the problem all along. If they had just replaced the outdoor unit then the problem would have been worse and they would be out a few thousand dollars and still no cooling. We finally did repair the system after finding some crud caught in the orifice. We are recommending changing the system to thermostatic expansion valves because I am getting a foaming sight glass and 80 psi of suction pressure. Which means the system cannot be properly charged.
The absolutely best thing that you can do to beef up a system that isn't working right (low suction pressure or icing on a full charge) is to beef up the indoor coil. Example if you have a 2 ton system consider either going to a 2.5 or 3 ton coil or a 3 ton system go to a 4 ton coil with a thermostatic expansion valve. This will take a system that just will not work right and give it a new lease on life. This is a good fix if you have restricted duct work or the system will not quite get the house cooled down (see also sizing and pool heating). Sometimes just adding a thermostatic expansion valve to an orifice system can solve problems. We did 3 of these upgrades this year (2001) 7 in 2002 with stellar results. The customers now report that they are "freezing their butts off".
Another system that we worked on is a Rheem oil furnace with a 1-1/2 ton heat pump and a fossil fuel kit. This system was condemned by the local utility Bge. B.G.Es repair division called B.G.E. Home (I call it B.G.E. Hose). They said that this system couldn't be repaired and the whole thing had to be replaced to the tune of about $5,000. We replaced the indoor coil with a 2.5 ton coil (with a thermostatic expansion valve of course) keeping in mind that this 1.5 ton unit is "too small" for this house and you would only see this size on an apartment or town house. After replacing the coil which had to be done no matter what since the old one had "Rheem syndrome". I advised the tenants that this system will work long hours and may not get the house as cold as they might want it on the hottest days. I since returned to fix a minor wiring problem with the oil burner and they reported that the whole summer it "froze them out". So much for the local utility being god.
This is a classic case of an indoor coil freezing up due to a lack of refrigerant or a stopped up metering device. Operating the system when it is too cold outside will cause the same symptoms. Normally the coil would be about the same temperature most of the way up and if this was caused by poor air flow it would tend to freeze the whole way and out to the outdoor unit rather quickly. This coil uses a Carrier Accurator system (click on image for a larger view) and should be changed to a Thermostatic expansion valve.
This system was mis diagnosed by our local utility BGE and they recommended changing the compressor which obviously is wrong or this coil couldn't ice up like this. According to the homeowner the tech they sent out also connected his gauges up backwards and was reading a suction pressure higher than the head which is impossible. They also didn't charge the system properly which is evident of the refrigerant surging in the liquid line and the suction reading 45 psi. So much for our local utility being God. Click here for proof.
I can understand a small contractor like myself making a bad call but with them there is no excuse. Take away the name and they would be out of business tomorrow. I am totally opposed to the local utility working on residential equipment for the simple reason that you the homeowner will think that you are getting the engineer that runs the power plant and they try to portray that their service is that good.
Procedures: First step: add a 40-80 Low pressure switch and anti-restart timer. Second step. If your system doesn't have one, add a TEV/TXV. Be sure to include a Sight glass and filter dryer. Third step: check your air flow and repair any leaks.
If you heat pump forms ice outside in the heat mode click here. If you have water leaking problems click here to solve it. For other heat pump problems click here. For other heating system problems click here. To schedule service in the Baltimore Washington Area, feel free to use this fill out form. Please include directions and contact info.
To learn about the proper charge or amount of freon in your system, which is directly related to the problems on this page click here.
Any other questions feel free to contact us by any of the means below. good luck Scott.
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Written By: Scott Meenen N3SJH of:
G&S MECHANICAL SERVICES.
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