AC dying...already replaced capacitor, now what?

ohlachesJuly 30, 2011

Hi All,

We have a Lennox heat pump that was installed by the builder when the house was built just over 10 years ago. I'm sure it was the cheapest builder grade available, since it was a spec house.

Lately, the AC has been quitting (it's been incredibly hot). During this time, the outside unit does nothing, but the fan in the basement unit runs. After a few hours (the length of time is getting longer), the AC will magically kick back on and seemingly work fine.

We had a technician come out about a week ago and he diagnosed a bad capacitor...said it wasn't totally shot, just going bad, which is why it would sometimes work and sometimes not. He replaced it, and the AC was working fine....until last night. It did the same thing. The blower in the basement was blowing, but the outside HP did nothing, until sometime this morning and it magically came back on.

We are about 3 months out on our new build, and really don't want to replace the whole AC unit. When we called the repair place today, the technician was kind of perplexed and said that unless it wasn't running he wouldn't be able to diagnose the problem (I think maybe he just doesn't want to come back on the weekend)...He said that it didn't sound like the compressor and really didn't offer much help. The problems with waiting until it quits again are obvious....any thoughts/suggestions that I could offer to repair technician? Right now I'd like to stick with the same company because they warranted their work.

Thanks!

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mike_home

Intermitten problems are tough to find. I'm not a professional, but it could be a thermal overload issue.

When was the last time you hosed down the condenser? There may be debris restricting air flow. Combined this with very hot temperatures and the compressor could be shutting down due to excessive heat.

    Bookmark   July 30, 2011 at 5:32PM
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brickeyee

"We had a technician come out about a week ago and he diagnosed a bad capacitor..."

Did he check the pressures on the unit?

This could be low charge, high temp, or even high pressure from restricted air flow through the condenser.

    Bookmark   July 31, 2011 at 9:43AM
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maryland_irisman

brickeyee's suggestion is a very viable possibility, especially on your unit. Those units have both, high and low pressure switches on them. It's quite possible the charge may be low and while sitting for an extended length of time, the heat causes the pressure to build up enough to allow the unit to start. One of the switches could even be defective which the intermittent condition points to. My suggestion is, if the tech returns and finds one of the switches to be defective, he should leave it in place and bypass it. Due to the age of your unit, it really wouldn't be worth the expense to evacuate the system, replace the switch and recharge the system. Many units do not even have them.
In addition to checking for air flow restrictions as brick mentioned, looking for loose connections in the compressor circuit may be a good idea. If it has an external overload relay on the compressor, that could be a culprit too and you don't really need an overload condition to make them go bad.

It wouldn't hurt to print this info out and show it to the tech. After being out in the heat all day, listening to anxious customers, fighting traffic, etc., he just might appreciate the suggestions.

    Bookmark   July 31, 2011 at 10:51AM
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maryland_irisman

Geez, the heat must be getting to me too!!! I should have also mentioned the contactor-relay may be marginal too. I have run into situations where spider webs, wasp nests or earwigs get between the points or the points are just so pitted or carboned up from arcing, they become unreliable. I'd also check the relay in the load center back at the blower unit.

    Bookmark   July 31, 2011 at 11:06AM
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dualref

And if you live in the south fire ants can get into your contact block. I always put in a few tbsp of Amdro at the bottom of the compressor to prevent them from coming in.
For some reason fire ants seem to be attracted to electricity.

    Bookmark   August 6, 2011 at 8:14PM
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brickeyee

"For some reason fire ants seem to be attracted to electricity. "

Electric things tend to be warm, if only slightly.

    Bookmark   August 8, 2011 at 7:59PM
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planewood

My compressor has a thermal switch in it. When the comppressor gets to hot it shuts the compressor (only) down. In this Texas heat it can take a long time before the compressor cools down enough for the switch to kick back in.

If that is the case, then you should determine why the compressor is over heating. Real low on Freon could be one thing causing that.

When this happens, can you hear the relay in the outside unit clicking in and out when the thermostat in the house is activated? If you do then at least your getting power to the outside relay coil and the relay is not stuck.

Another posible reason for the compressor overheating is an obstruction inside the copper lines occasionally blocking the flow of Freon. Something like this most likely would occur at the expansion valve inside the house. But, I would think this would be a rare thing to happen.

    Bookmark   August 9, 2011 at 12:55PM
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heatseeker

the tech should be able to identify if the compressor is failing i would get second opinion.

    Bookmark   August 16, 2011 at 1:39PM
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cbernot

Ohlaches, I believe I ran across pictures of your new build with pewter gray shingles. I have been agonizing over shingle colors. Could you share the specific brand of your shingles ie Timberline HD or ultra HD pewter gray or is it another brand. Thanks. Really love your roof.

    Bookmark   February 27, 2013 at 10:40PM
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