# Older Carrier Hvac question



## 618672 (12 d ago)

The air handler is working as expected including Aux heat but the compressor and fan will not start. I can see that Low voltage is kicking on the contactor. I went ahead and replaced the Contactor and the Capacitor even though both tested "OK" it was time to replace the Contactor.

It seems like it is not getting any high voltage I checked all of the fuses and breakers they tested fine. I am going to double-check tomorrow it got dark and started raining before I could confirm.

What would cause the compressor AND fan to not start? I feel like it must be a bad switch or control board.


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## Ben.Wolfinger (22 d ago)

618672 said:


> The air handler is working as expected including Aux heat but the compressor and fan will not start. I can see that Low voltage is kicking on the contactor. I went ahead and replaced the Contactor and the Capacitor even though both tested "OK" it was time to replace the Contactor.
> 
> It seems like it is not getting any high voltage I checked all of the fuses and breakers they tested fine. I am going to double-check tomorrow it got dark and started raining before I could confirm.
> 
> What would cause the compressor AND fan to not start? I feel like it must be a bad switch or control board.


I’m betting there is a short in either the red or white thermostat wires running to the contractor. You can confirm this by wiring both wires together at the contactor. Remove both wire nuts where the condenser wires are connected. Rewire both red and white to one side of the contactor. Then remove the wire from the other side of the contactor (the side that isn’t connected to anything anymore) and wire that directly into the grounding block on the condenser. Back inside, at the control board, you will need to wire the yellow thermostat wire and both the red and white condensing unit wires, together at the position labeled “Y” or “Yellow” on the control board. All you’re really doing is effectively changing the ground position from inside to outside and banking on the fact that only one, but not both of the condenser wires have a short.


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## Ben.Wolfinger (22 d ago)

Ben.Wolfinger said:


> I’m betting there is a short in either the red or white thermostat wires running to the contractor. You can confirm this by wiring both wires together at the contactor. Remove both wire nuts where the condenser wires are connected. Rewire both red and white to one side of the contactor. Then remove the wire from the other side of the contactor (the side that isn’t connected to anything anymore) and wire that directly into the grounding block on the condenser. Back inside, at the control board, you will need to wire the yellow thermostat wire and both the red and white condensing unit wires, together at the position labeled “Y” or “Yellow” on the control board. All you’re really doing is effectively changing the ground position from inside to outside and banking on the fact that only one, but not both of the condenser wires have a short.


 The system will run just fine like this too by the way. But you do need to make sure that unused contactor wire is grounded really well to the grounding block on the condensing unit. It can be difficult because that wire is so much smaller than the ground wire that’s already there. Make sure the contactor wire is directly on top of the other ground wire and right in line and in front of the grounding screw. Use a flat head screw driver to tighten the hell out of that grounding screw.


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## 618672 (12 d ago)

Thanks for the reply I got it fixed but do have one very I'm not HVAC guy question. I installed a new capacitor and assumed they charge instantly when the power gets restored to the system is this true? if so then the problem had to be a dumb mistake on my part.

The disconnect has gotten a little rough and I think I was not getting it inserted well enough. I have pulled it a few times over the years and never had any issues but I went out today to test the voltage and had not made any changes except for pulling the disconnect. the system started right up so I have to guess it was my dumb mistake.


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## Ben.Wolfinger (22 d ago)

618672 said:


> Thanks for the reply I got it fixed but do have one very I'm not HVAC guy question. I installed a new capacitor and assumed they charge instantly when the power gets restored to the system is this true? if so then the problem had to be a dumb mistake on my part.
> 
> The disconnect has gotten a little rough and I think I was not getting it inserted well enough. I have pulled it a few times over the years and never had any issues but I went out today to test the voltage and had not made any changes except for pulling the disconnect. the system started right up so I have to guess it was my dumb mistake.


It’s hard to explain on a forum without being able to draw you a diagram, but the way capacitors work is this, yes the begin to charge immediately but then discharge just as fast. This process happens over and over and over. That’s why when you pull the capacitor, sometimes it will be charged still and other times it will not be. That’s also why I always discharge them to ground immediately after pulling them. If you pull the capacitor at just the right spot, as the alternating current wave is directly inline with the electromagnetic field it’s producing, the capacitor will still have a charge, however, if the capacitor is pulled when the AC current wave is at any other location, the capacitor will NOT be charged. As I said, a diagram would be super helpful right here lol. At any rate, glad you got it going!


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