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HVAC outside unit not working

Posted by sn002 (My Page) on
Sat, Jun 30, 12 at 22:06

My unit is 10 years old. The outside unit won't start so I did a little research
to find out the contactor didn't close by itself when I turned on the thermostat to cool.
I went a head and replaced the new contactor. Now it is closed by itself when I turned on the unit. But it is still did not work. All I heard was like a brief humming sound and the fan did spin just a little bit then stopped. The inside unit is working fine...the blower blows out air but not cool air. Please advice. Thanks

Last year I put in a new capacitor everything working fine until today. so I believe the capacitor is fine.

Follow-Up Postings:

RE: HVAC outside unit not working

Are you sure all the wires are in the correct place? You've checked to ensure you are getting 240v to the contactor and beyond? With 240v you should get 120v between each hot wire and ground and 240v between the two hot wires.

RE: HVAC outside unit not working

Here is how I tested the contactor. Turned on the unit from the thermostat to energize the coil so the contactor closed.

I got 24v on the contactor coil voltage. Got 240v on the bottom hot wires incoming power from the disconnect box. Got 240v on the other end of the contactor (coming out). Got 0v from each bar of the contactor so that means they are closed circuit. Got 120v between each hot wire (in/out) and ground.

I got a different reading if I tested without turning on the unit from the thermostat.

One question though. What is the correct way to test the contactor with or without the unit on?

RE: HVAC outside unit not working

Don't assume the capacitor is good because it is a year old. New capacitors have been known to fail prematurely.

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