Condensing Unit Not working

Old 09-23-02, 09:46 AM
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Unhappy Condensing Unit Not working

A few weeks ago my AC unit outside stopped cooling. The furnace fan blows and the unit outside has a electrical humming sound but the fan is not spinning. Could something be caught in the fan? What are my options short or calling in a HVAC technican to look at it.
Old 09-23-02, 10:52 AM
Jacque Schidt
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How loud is the humming?

A low, barely audible hum could be the contactor closed, but no voltage is flowing. A loud num that changes pitch is a sign your compresor is running but the fan is not.

Here are the things I'd do:

Check the breakers serving your outdoor unit. There may be more than one. Even if it looks like it is on, turn it off, then on again.

There should be a disconnect or switch at the outdoor unit as well. It may have breakers or fuses in it. Check that also.

Before recommending any further action on your part, I'd want to know how much electrical knowledge and experience you have. I'd hate for you to get shocked and it be our fault.
Old 09-23-02, 10:56 AM
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The "hum" is loud enough to suggest the motor is trying to spin the fan. I just recently bought the house and have looked at the unit before when it was working.

As far as my electrical knowledge, it's ok. I'm a architect and know that much. The disconnect box is difficult to get to and the last time I could not open it. Can I use the breaker inside the house to disconnect the unit from the power?
Old 09-23-02, 02:25 PM
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Yes you can, but be careful and test the power leads inside the unit before you stick your hands in there. Inside the control box for the outdoor section, look for a large relay which is known as the contactor. Is it pulled in? Test for power on both the incoming side and the load side. Should be about 240 volts. see any burnt wires? What happens when you spin the fan blade? Locked up or spins freely? Look at the contact points on the contactor. Do they look burnt or full of ants? Check these items and let know what you find.

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