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Old 08-29-2014, 11:39 AM   #1
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Outside AC unit not working


My house started getting really hot, so of course I checked the thermostat. Was set to 71 while actual temp was 81. There is air blowing out of the vents, but not cold air. I went outside and checked the outside unit and the fan was not spinning. I put my ear to it and there is a very slight humming, telling me there is power. At first I thought capacitor, but the stick test did not get the fan blades moving. Any ideas? Thanks!!

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Old 08-29-2014, 12:29 PM   #2
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Outside AC unit not working


humming could be contactor coil being energized, but breaker could be blown. check for 240 to outdoor unit and 24 volts to contactor coil, are you capable of checking for power with a meter?

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Old 08-29-2014, 01:26 PM   #3
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Outside AC unit not working


Thanks for your reply HVACDave! I know the main circuit breaker (in my main electrical panel) is OK because it is not tripped (already checked that), but there are a couple of fuses in it's own separate box mounted on the outside of the house by the AC unit. Is it possible these are blown and the 240 isn't getting to the outdoor unit? I didn't really think it would be a blown fuse due to the slight humming, but your post makes me think differently now.
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Old 08-30-2014, 12:24 AM   #4
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Outside AC unit not working


capacitor. is the compressor running while the fan is not? ice forming along refrigerant line mainly the bigger one that is insulated?

if nothing is coming on outside, compressor and fan than it's either a capacitor and/or high voltage, breaker. Mind you a breaker can appear to be "on" but may need to be reset regardless.

low voltage from inside at furnace.air handler is what powers the contactor thus the humming from contactor.

open service panel and look at capacitor, if it's bulged on top or jelly type substance is seeping from it it's bad.
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Old 08-31-2014, 02:05 PM   #5
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Outside AC unit not working


Thanks for the reply guys! I changed the fuses on the outside and the outside fan works again!! However it's making a weird surge sound every 30 secs or so.. Is that normal?
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Old 08-31-2014, 04:04 PM   #6
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Outside AC unit not working


Is it cooling your house now? There is a reason that your fuse(s) blew and you should get someone to check it out unless you want to dig into it yourself. Bad compressor or maybe capacitor comes to mind if the unit isn't cooling.

Last edited by zappa; 08-31-2014 at 04:11 PM.
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Old 08-31-2014, 06:27 PM   #7
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Outside AC unit not working


Fan is running and air is cool now coming out of vents after 30 amp fuses were changed on outside fuse box (for AC only) but that surge noise happens every 30 secs.. Even though it works, I decided to leave it off because of that sound. Does that sound soud familiar to you? Almost sounds like just before a transformer blows
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Old 08-31-2014, 06:59 PM   #8
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Outside AC unit not working


Quick update, I took off the service panel and took a look. The capacitor look ok as it's not puffed out. However, that surge sound i mentioned is electrical arcing. There are burnt wires on the relays. Possible bad relays? Or signs of a much bigger problem?Thanks!
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Old 08-31-2014, 07:23 PM   #9
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Outside AC unit not working


Hard to say....arcing and burnt relays still shouldn't blow the fuses unless it's so destroyed that there is a short circuit between the phases or to ground. Wires, internal capacitor short to case, compressor and fan motor windings are also suspect.

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Last edited by zappa; 08-31-2014 at 07:31 PM.
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