Air Conditioning Won't Turn On

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  #1  
Old 10-01-18, 08:42 PM
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Air Conditioning Won't Turn On

I have an air conditioner and heat pump.

I fully tested my circuit board for 24 volts, and made sure my transformer was working. I also tested R to C for thermostat on circuit board and it was 24 volts.

I bought a new capacitor, tested it, and installed it in my outdoor unit. My contactor is getting 24 volts, and I can turn the outdoor unit on by physically engaging the contactor.

Heat and air conditioner still won't come on. I get a click from the thermostat and hear nothing from my indoor unit or outdoor unit.

I did notice the system start firing up when I was wiggling the furnace access panels around on top of the switch, but it went away. I could not emulate this by continually trying to push the control panel safety switch in.

Any ideas?

Thanks in advance.
 
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Old 10-02-18, 04:46 AM
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When the thermostat is calling for cooling, check the voltage between the Y and C terminals on the thermostat. It should read ~24VAC when calling for cooling, and 0 when it's not.

If you have 24VAC between Y & C, go to the outside unit and check the voltage across the two wires coming from the house (signal wire, not the 240VAC wiring). With the thermostat calling for cooling, you should have 24VAC at the wire nuts where the signal wire connects to the internal wiring of the outside unit.

Report back on what you find.
 
  #3  
Old 10-02-18, 08:24 AM
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Thanks.

I should have added that, when this issue first popped up, my thermostat was on. After going in the attic and testing my circuit board, I think I saw a little spark, and now the thermostat screen wont come on. When you put new batteries in, it just lights up for a second, and turns off. Did it get fried?

Another thought...several months back there was white powder on the thermostat battery terminals. What does that mean?
 
  #4  
Old 10-02-18, 09:47 AM
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Since the thermostat screen isn't lighting up, it sounds like the thermostat may be fried. The white powder is almost certainly from a leaking battery. You should be able to clean up all the powder and make sure the battery terminals are clean with no corrosion on them. Of course, if the thermostat is fried, there may not be much point in worrying about the battery terminals.

If you want to rule out the thermostat, connect the R, Y, and G terminals of the thermostat together. If everything is working okay, that should make the outside unit and the inside blower turn on and start cooling.
 
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