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stlsig · 05-29-2010, 11:27 PM

Today my AC stopped working correctly. The compressor was working, but the fans, while clearly getting electricity, wouldn't kick on. My HVAC man (who has serviced these units for 30 years) tested the electric coming into the fans. This is a 120 v circuit and with the fans off it was drawing about 108 v and then once we kicked the fans on, it dropped to 105 v. Thus there wasn't enough electric to get the fans on.

FYI - After the fact, The HVAC man took one fan home to test it, it worked fine.

We then tested all the other outlets in the house and sure enough, they are all drawing the same voltage. We also tested the convenience outlet at the main panel, same results.

Does anyone have an idea what is causing this? We cant get the AC operational until this is fixed and I'm concerned that it might be a much lager issue than just one circuit.

Thanks,

**kok328** · 05-30-2010, 05:43 AM

If your at all comfortable working with electricity; remove the cover panel from you load center and check voltage from leg1 to ground, leg1 to neutral, leg2 to ground, leg2 to neutral and leg1 to leg2 (for 240V).
If these check out to be 120V then you have a problem with your load center and need to check for loose connections and/or call an electrician.
If they check out to be 108V then you have a problem with your service and need to call your local utility provider.

Wuzzat? · 05-30-2010, 07:13 AM

Quote:

Originally Posted by stlsig

This is a 120 v circuit and with the fans off it was drawing about 108 v and then once we kicked the fans on, it dropped to 105 v.
Does anyone have an idea what is causing this?

Yeah, it's a high resistance upstream of your AC, possibly caused by a loose connection.

Being careful of arc-flash, and using a 20A, 240v load like a wall oven or an elec. dryer, measure the 240v at the panel.
When you switch off the wall oven the voltage should go up no more than ~0.4vac. You'll need a DVM to measure a change this small.
You're looking for the change in voltage. It may be somewhat larger than 0.4vac, depending on how far away you are from the pole transformer.

stlsig · 05-31-2010, 10:11 AM

I have an electrician coming tomorrow to check everything out. I appreciate all of your knowledge.

JoeD · 05-31-2010, 04:20 PM

Call the POCO. It is likely it is their problem. Did the HVAC tech measure the 240 volts? I bet it was low as well.