AC will not turn on unless reset

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  #1  
Old 06-30-15, 01:12 PM
J
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AC will not turn on unless reset

I have a gas furnace and central air with condenser outside.
The AC works just fine in the evening, turning on and off as it should with the thermostat. But at some point during the day it stops being able to turn itself on.
At this point, the thermostat will show "Cooling" but the AC is not on.
At the furnace, I can hear it clicking, trying to turn on the AC repeatedly.
If I reset it at the breaker, HVAC switch on the wall by the furnace or the cut-off switch inside the furnace (off, then on after a few seconds) then the AC turns on immediately.
I have recently replaced my thermostat so I know that's not the problem.

I found this old thread that had the same issue:
http://www.doityourself.com/forum/ga...ker-reset.html

In that old thread they suggest replacing the breaker.
I don't see why it would be the breaker if it is not getting flipped and since the furnace is still operating during this issue (making clicking noises trying to turn on the AC)
Does anyone have any suggestions before I resort to calling in a professional to help me investigate? And possibly an electrician to replace the breaker.
Thanks in advance.
 
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  #2  
Old 06-30-15, 03:18 PM
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Just to clarify the problem, when it acts up, what isn't turning on: the blower on the furnace, the outside (compressor/condenser) unit, or both?
 
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Old 06-30-15, 06:29 PM
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Welcome to the forums.

You may need a voltmeter to make some measurements. Do you have one ?
I severely doubt it's a breaker issue.
 
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Old 06-30-15, 10:09 PM
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@Bob14525: Both do not turn on.

@PJmax: No I don't have a voltmeter. I really need to get one as I keep finding reasons to have one. Will any voltmeter work for testing this kind of problem? I found this one on Amazon http://amzn.com/B00KHP6EIK

Forgive me if I don't reply to this post for a while, I'm going on vacation for a few days.

Thanks.
 
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Old 07-01-15, 04:05 AM
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The Amazon multimeter you referenced will work fine for general testing. If you have a Harbor Freight store near you, they have a comparable unit for under $10.

Let us know when you're back from vacation and have a multimeter and we'll give you some things to check.
 

Last edited by Bob14525; 07-01-15 at 06:42 AM.
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Old 07-01-15, 05:59 PM
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Since it happens during the day, It sounds like the compressor is going off on high head pressure. You may get lucky and get away with just changing the capacitor or it could be the condensing fan motor. I recommend changing all capacitors and installing a hard start kit first.

Good luck!!
 
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Old 07-01-15, 08:36 PM
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The caps could be at issue but I'm not leaning in that direction. The OP turns AC power off and back on and the A/C starts fine. I'm leaning towards a control issue. The 24vac needs to be checked to the condensor unit first.
 
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Old 07-02-15, 09:10 AM
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Remember: your Hi & low pressure switches, safeties all run through your 24 volt circuit. Trust me, start there. It could be a number of issues but we see this happen everyday.
 
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Old 08-16-15, 06:14 PM
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Hi guys, I'm back. I meant to get back on here and reply when I got back from vacation but I got busy and forgot about it. I haven't had this issue that much until recently, when it got to be in the 90's a lot more.

@NJHVACTECH: I don't know where those capacitors are or the hi and low pressure switches. I would need more info on that.

@Bob14525: Where and what would I need to test with my multimeter to start?

Thanks again for your help.
 
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Old 08-17-15, 04:37 AM
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You'll have to remove the side cover from the outside unit. When your A/C isn't working, take your voltmeter, set it to AC volts and measure the voltage across the side terminals (small diameter wires) of the contactor. The contactor is a rectangular relay. The 240VAC power wires attach at both ends of the contactor, input voltage at one end, the output voltage (that feeds the compressor & condenser fan) at the other end. When the thermostat calls for cooling, it sends 24VAC to the contactor coil (side terminals), which energizes the contactor and pulls the contacts down to turn on the outside unit.

So, when the A/C acts up, check to see if you have 24VAC at the side terminals of the contactor. If you don't (and I expect that you won't), then check for 24VAC where the small diameter wire (control signal voltage) comes into the outside unit from the house. The 24VAC wires from the house should connect to the internal wiring of the outside unit using wire nuts. If you have 24VAC where the wires come into the outside unit, but not at the contactor side terminals, then you likely have an open pressure switch. You'll have to check the wiring diagram or follow the 24V wiring from where it comes in until it reaches the contactor. It likely will pass through one or more devices before it gets to the contactor.
 
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