# AC problem diagnosis



## mackiee (May 20, 2010)

Hi,
I need a hand diagnosing the issue causing my AC not to turn on.  My AC won't turn on but the furnace blower is running. I have a Carrier furnace and an Optima 2-s AC

I've checked that the thermostat is turned to cool and set to a low temp. I've checked all the breakers and service shut offs. The power on the furnace control board is 26VAC between COM and Y.  So I have a feeling it is something within the AC unit itself.

It looks like thermostat is telling the furnace to cool so it relays the message to the air conditioner but it is not turning on. What should I check next?

Thanks in advance


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## Wuzzat? (May 21, 2010)

Is the outside compressor fan running?
Can you post a schematic?


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## kok328 (May 21, 2010)

Do not post a schematic, it is of very little help and somewhat redundant to a person that knows HVAC troubleshooting.
You should check to see if the 24 (26V) is present at the contactor coil in the compressor unit.  Also check to see if you have 240V on the line side of the compressor contactor.  If you have 240V on the line side of the contactor but, not 24V to the coil of the contactor, they you may have a stuck/bad switching relay.
Also, check to see if someone installed an add on pressure switch that needs to be manually reset.


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## NitroNate (May 27, 2010)

i'm no expert, but i had a similar problem awhile back. neither the fan nor the compressor would turn on because the capacitor was shot. replaced the capacitor for like $12 and it was good to go.


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## HardcoreNinja69 (May 28, 2010)

I have a similar problem with mine and fan runs but the compressor tries starting a few seconds and quits. I am trying the capacitor replacement. I have my fingers crossed.


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## khorn (Jun 17, 2010)

I just put in a new heat electric heat pump and now I have no power at the thermostat. I cant even get the temp reading on thermostat to work. I put existing thermostat wires to outside heat pump while I had power to the thermostat. What did I do?

Thanks!


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