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Tim H.
Tim H., HVAC Professional
Category: HVAC
Satisfied Customers: 3971
Experience:  Experienced in all aspects of HVAC, both residential and commercial.
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My home AC system is not cooling. The system is operational,

Customer Question

My home AC system is not cooling. The system is operational, but is not sending the signal to kick on the outside unit (condenser). I was able to temporarily start the unit with the push button relay. Any help in diagnosing this issue would be greatly appreciated!
Submitted: 5 months ago.
Category: HVAC
Expert:  Tim H. replied 5 months ago.

Hi, I'm Tim and I'm an HVAC expert here to assist you with your questions. Please provide all information I request as it makes it more difficult to troubleshoot something when I'm not there onsite. Essentially, you become my eyes and ears. Thanks for the opportunity to help. At the end of our dialog, you will have a chance to rate my service, but please wait until we are finished and you're satisfied you have all the information you need. Please be patient as many times we work with several customers at once.

Could be a bad thermostat. Have you tried bypassing the thermostat?

Customer: replied 5 months ago.
My thermostat is digital and was upgraded last year when I had a service call.I have not tried bypassing the thermostat. What's the easiest way to do that? I have a decent set of tools and multi-meter available as well to check voltages.Also, when changing the system from OFF to COOL, I do hear an audible click.
Expert:  Tim H. replied 5 months ago.

To bypass the thermostat, turn furnace or air handler power off, take the front section of the thermostat off the wall, loose from the back section (called subbase). You will see the thermostat wiring. Take the red wire on R or RC-RH, yellow or blue wire on Y, and green wire on G and twist the ends of these together. Then power back on. See if A/C now runs.

Customer: replied 5 months ago.
Alright, I got the wires connected and there was no change in status. The AC unit is still not blowing.
Expert:  Tim H. replied 5 months ago.

If fuses are good and no tripped circuit breaker, then you either have bad wiring from inside unit to outside, or the unit is locked out on a low pressure switch or timer. Get a voltmeter and check across the two low voltage wires that come from inside to outside unit for 24 volts AC

Customer: replied 5 months ago.
The thermostat wiring was also replaced last year when the thermostat itself was upgraded. The new thermostat required an additional wire so that it could communicate properly (added the humidity sense feature).Where would I find the low voltage wires from the inside? Do you mean on the condenser unit outside my house, or the circuitry near the fan and coils in my crawlspace? This is a image of my condenser wiring: http://imgur.com/WEeHAEC
Expert:  Tim H. replied 5 months ago.

There would be two wires that go from inside unit to outside to activate contactor. This is where I want you to check for voltage.

Expert:  Tim H. replied 5 months ago.

I have to leave for a bit, but will check back later when I return

Customer: replied 5 months ago.
You are correct. The two wires running from inside read 0.0 Vdc.
Expert:  Tim H. replied 5 months ago.

If you have thermostat jumped as indicated above, then you have bad wiring somewhere.

Customer: replied 5 months ago.
OK, I am still tracing the wiring and checking the voltages. I will need to continue tomorrow.
Expert:  Tim H. replied 5 months ago.

OK, Let me know if you have additional questions. Otherwise, good luck! Thanks for using Just Answer and please don't forget to rate my service as that's how experts get paid (thanks in advance for any bonus left). Otherwise experts work at their own time and expense. Even though the Just Answer site has your money on deposit, it does not get transferred to me until you (positivelY) rate my service. Feel free to post back with any more questions. Remember, you can rate question at any point and still ask more questions (related to the same thing) later on. Experts prefer if you rate question at the end of our first chat.