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Tarheel Technician

A/C window unit cool but not cold

13 posts in this topic

Got a a/c that when running, only two rows of the coils frosts up. They don't just sweat like normal, they frost up....but only two rows. I'm guessing that there is either a sealed system restriction or a low charge (freon leak). Is there anything else I should be looking for?

Thanks.

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Need appliance parts? Call 877-803-7957 now!

   I would be suspect to a low charge. However, are both sets of coils clean, especially the evaporator coils inside  ? I would verify proper unrestricted air flow, before jumping the gun.:cool:

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I took the unit out and cleaned all the coils thoroughly. After that, it cooled a little bit better, but still not cold enough. Running it inside the shop (around 76 degrees), it put out about 63 degree air, and it still had frost on two rows of coils at first. So I'm assuming it may be low on freon.

I had a formal training class on sealed systems, but it has been a few years ago. Been doing appliance repair a few years, but not any sealed system work. We have the equipment here at the shop that the previous tech, who did sealed system work, used. What is the best way to determine if and where a leak is? Bubble solution? If freon is added, can it be added without purging the system first? Just looking for some direction.

 

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Hello

Sounds like a window unit. Soap bubbles can be used, but an electronic or halide torch leak detector would be better. Just look really carefully with the bubbles. 

If U have a gage set, unless someones already added some, your gonna have to go to a HVAC supply house and get a (2) inexpensive multi-pipe size Tap-a-Line valves. Very easy to use. Be sure to use the correct insert for your size pipe. The valve should not be loose on the pipe nor should it be crushing the pipe. Follow the directions. Word of caution-there is probably gonna be a very small black rubber o-ring included with ur valve. Very easy to loose. Don't loose it!!

Most compressors have a process tube on them. Look 4 piece of copper pipe coming off comp going to nothing and crimped on the end. Install 1 valve on that pipe(between the comp and the crimp). Thats ur suction (low, the blue gage:)) side connection.

Next look @ the compressor. The 2 pipes connecting 2 it. 1 line is bigger then the other. U want the smaller 1. Install a valve on it. Thats the discharge (high side, the red gage;))

Make sure your hoses are connected tight on the manifold. Hook up the gages. With unit off both gages should read at least 125psi @ 70 degrees ambient temp. Unless its really cold they shouldn't B much lower then that. If they are lower, U have a leak. 

Hope that helps:)

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my first test would be to disable the fan,remove the anticipator from the evaporator so it doesn't freeze and shut the unit down- pin the t'stat to constant operation and run for a while, you should get a full frost pattern,if not, look carefully at the tubing as if there is a leak,there is always oil with it. look particularily at the areas where the tubing runs horizontally under the condensor- worst comes to worst- discharge unit into a recovey bag(careful as charge is big and usually r-22) and see how much comes out, most shakers use rotary compressors and you may have a failed or failing reed valve in the compressor.

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Hooked up the gauges on the unit, and I have about 115 -117 psi on high side and low side with unit off.

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Well, since you've got the gauges on it,fire it up and see what your readings are. Let us know.

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Fired it up.......the pressures read as follows:

Low side went down to about 6 psi, while the high side went up to about 130 psi. After it ran for about 5 minutes, the high side was up to about 165 psi and the low side had risen to about 33 psi. After 5 more minutes the pressures were about 170 psi and 35 psi.

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Also noticed that the frost would go across one row of coils....then come back to about half way, then go towards the end again and then come back. Is that an indication of a restriction, or is that a possible compressor problem?

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use a clamp on ammeter to see what the amp draw is while running ,if its above the norm for the unit ,I would say you have a restriction ,that is if you only have 35 psi on the low side. low side operating psi should 68 psi ,that would give you 40 degrees across the evap coil. To see if a unit has enough freon in it without a tap I place a piece of cardboard over the evap and I also move the sensing bulb out of the way and let it run. If frost creeps back all the way to the compressor then she has enough freon. 

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Hello

Ok. It sounds like U R short of gas. Couple more checks should do it. Is the unit using R-22? If it is and U have a Temperature/pressure (T/P) chart, start the unit again and let the pressures settle out. Measure the ambient air temp (room temp), add 30 degrees to it. Find that temp on the T/P chart and then read the corresponding pressure 4 R-22.

Example-- room temp =70 degrees. Add 30. New temp is 100. At 100 degrees your head pressure (high side) should B approx 200psi (+-15 psi ). We can also say that at 200 psi head pressure ur suction (low side) should B approx 60 psi(+-5psi) Now U know what ur pressure should be(approx). If its 80 degrees, then head pressure would B 230 psi 4 R-22. U have to adjust accordingly.

So ur running @ 165 hi and 35 lo.  Hook up to a tank of R-22, purge the air out of ur gage hose and add some gas to the unit slowly thru the lo side. Watch ur hi side gage to C if the pressure starts to rise as U add the gas. If it does thats good. Bring UR hi side pressure up to 200 psi and stop. Has the low side gage pressure also gone up? If yes, then most likely U have lost some refrig to a leak. Although with window units it can B tricky.

They hold such a small charge that if many ppl have hooked up to it with gages, over the years they have actually taken enough refrig out to make it look like U have a leak. A six foot refrigerant hose can hold approx 2 oz of refrig. After 4 hook ups, if no one adds refrig, U are now down 1/2 lb of refrig. If the unit only holds 34oz full charge, UR now down 1/4 of the full charge;) with no leak.

If both of UR pressure rise when U add gas then continue to add gas until U reach the desired head pressure you figured out earlier. Once U reach good pressures take a thermometer and measure the return air temp to the unit and the cold(supply) air out. UR looking 4 a 20 degree spread(+-4 degrees, 18-22) 

If U have that U can now either start looking 4 a leak or let the unit run 4 a day or to and C if your pressures start to drop again. Set it at a normal temp and let it cycle on and off.

If U add gas and the pressures don't start to rise then U may be dealing with a restriction.

Hope that helps.

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Thanks for all the info and help. Just to update on this unit, I added freon to the unit until the pressures were up to 230/70. The unit stopped frosting up across that one row of coils, and cooled very well. After letting it run for a few hours, the high side pressure had dropped a little bit, and a couple of days later, the high side pressure would only reach 215. So I think I have a leak somewhere.

Again, thanks for the help, I've learned a lot.

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Hello

U are welcome:) That 230/70 sounds great. Don't let the fluctuation in head pressure throw U. If the OAT(outside ambient temperature) has gone down , so will UR head pressure. Vice a Versa if the OAT has gone up. U must always check Ur running head pressure against UR T/P chart and the OAT  at the time.

If both of UR pressures continue to fall, then yep, U have a leak.

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