outdoor a/c unit won't cut on


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Old 04-20-16, 02:59 PM
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outdoor a/c unit won't cut on

Hello all, I went to cut my a/c on for the first time this year and the outdoor unit won't cut on at all. It is new, was replaced last summer and worked the remainder of the summer, but this year... nothing. The air handler kicks on and starts circulating air, but the outdoor unit does nothing--no noises, movement, etc.

In the picture below, the large black part with 4 big terminals does have 220V to the bottom of it (black/red wires), but no voltage on the top terminals. The capacitor doesn't appear to have bulged ends. What should I check to further troubleshoot?

Thanks.

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Old 04-20-16, 03:33 PM
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With the outside unit turned off (there should be an electrical disconnect nearby), and with the thermostat calling for cooling, measure across the side terminals (yellow & blue wires) of the contactor (large black part you mentioned). Ideally, you should have ~24VAC across the terminals. If you have ~0VAC, disconnect the two orange wire nuts (bottom of your picture). This is where the 24VAC control voltage from the house connects to the yellow & blue wires connected to the contactor. Make sure that the wires that you disconnect don't touch each other or any metal (chassis).

If you have 24VAC across the two wires coming from the house, but nothing at the yel/blue wires on the contactor, you may have a low pressure switch that has opened due to low refrigerant charge.

If you don't have 24VAC across the two wires coming from the house, you probably have a broken wire coming from the house (animal may have chewed through it). Check the wiring carefully coming from the house.
 
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Old 04-20-16, 04:14 PM
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Thanks for the reply & info Bob! I have good news and bad news. Initial reading on the blue/yellow terminals was 1.5 vac. I traced the wires to the house, and found a broken wire in a wirenut. I fixed that and now have about 26 vac at the yellow/blue terminals on the contactor.

However, I cut the power back on to the outside unit, and turned the air on, same symptoms. I verified with everything back on that the blue/yellow wires have the ~24vac when the thermostat is telling it to run.
 
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Old 04-20-16, 05:20 PM
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The contactor is a relay. The 24VAC control voltage comes from the thermostat and closes the relay, sending 240VAC to power the compressor and condenser fan. Since you now have 24VAC at the contactor, very carefully check to see if you have 240VAC between the two terminals on top of the contactor (red & black wires). If you don't have 240VAC across the top two terminals, the contactor may be defective. Sometimes you can push in on the center of the contactor (use a non-metallic tool such as a piece of wood or plastic) to force the relay contacts to close. If the outside unit turns on and runs normally (contactor pushed in), everything else would appear to be okay, and you may only have a bad contactor (relatively inexpensive).
 
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Old 04-20-16, 06:12 PM
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Bob, thank you so much, I think you found the problem! 0.00 VAC on the top terminals, so I manually pushed the center of the relay in & it cut right on!

It has a 10 year parts warranty on it, so I'll contact Goodman tomorrow to ask for a replacement contactor, and it's only 10 months old. It scares me that a part failed that quickly.

I am fairly confident that I can replace it myself to avoid a service call. It appears there are mount screws holding the contactor to the surface.

Thanks again, I really appreciate it!
 
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Old 04-21-16, 11:37 AM
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Update: I found a replacement locally for $14 today and installed it. The unit fired right up and is working fine. Hindsight before, I never heard the contactor clicking as the mechanical functions of relays do. I avoided a service call, & safely resolved my problem for 14 bucks. I'm ecstatic, thanks again for the help Bob, you saved me a ton & taught me about the system!
 
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Old 04-21-16, 01:04 PM
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Glad to hear that you got it working and thanks for reporting back. Happy I was able to help.
 
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Old 04-21-16, 03:53 PM
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Many times you don't actually hear the contactor close due to the noise from the compressor and fan starting. If you turn the power off at the condensor you'll hear, or should hear, the contactor loud and clear as it gets its power from the inside unit.
 
 

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