Heating issues


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Old 11-14-14, 05:02 PM
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Heating issues

Hi,

My HVAC system has been giving me some grief the past couple of days. With the thermostat set to heat the system will turn on and provide heat throughout the house. However, there is an audible buzz sound as the exterior unit (air condenser) turns on and this sound is repeated at the breaker panel, as if the unit is causing a large draw on the circuit. This buzz does not trip the breaker, and my initial assumption was a bad breaker, which has been replaced but did not remedy the problem. My next assumption was a bad capacitor, and when I tests it, it returned about 30 micro F on the HERM side (for a 45/5 capacitor). So, i replaced the capacitor, but to no avail the unit still buzzes.

The buzz is a very short intermittent buzz, approximately one buzz every 30 seconds to a minute. The Buzz comes as the air compressor's fan turns on, or at least appears to turn on, as it spins freely but never reaches a high rpm. Is this a sign of a bad fan motor or a much more involved electrical issue?
 
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Old 11-14-14, 05:38 PM
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Welcome to the forums!! My best guess is the buzzing noise is coming from the contactor. It may also be a loose wire. The contactor will look similar to the attached photo. There is a 24V coil on it.
 
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Old 11-15-14, 07:02 AM
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Thanks for the info, I have tested the voltages across T1/T2 and L1/L2 and gotten roughly 120 VAC. Does this indicate a bad contactor?
 
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Old 11-15-14, 07:11 AM
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You should be getting around 240V across L1 and L2 (incoming voltage). It seems you have lost one leg of incoming voltage. I suggest you check your disconnect to check the voltage there. If you have a cartridge type fuse disconnect you may have a blown fuse. If you have breakers check those to see if tripped. You should not be getting voltage across T1 and T2 until the plunger in the middle is pulled in by the 24V coil with a call from the thermostat.
 
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Old 11-15-14, 11:31 AM
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Thanks again!

I checked the Fuses and one of the two tested bad. So, I replaced both. The system blew one of the two fuses immediately and tripped my a/c unit breaker. Do you think this is a sign of a much larger electrical issue that will require an electrician or HVAC specialist?
 
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Old 11-15-14, 12:02 PM
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It could be anything from a loose wiring connection to a bad compressor. As a beginning, I suggest turning off the power that supplies the fuse that blew. Verify power is off with meter before proceeding. Then inspect the fuse box for any obvious burnt components/wires. Also, inspect the circuit breaker that protects the disconnect box for loose connections. Make sure all of the wires are tightened down on the lugs. Then check all of the wires in the compressor area to make sure there are no burned wires going to the run capacitor or contactor.

You need to measure current draw on the unit with a clamp meter at start up and run cycle to determine if it drawing too many amps. A bad run capacitor will hinder quick starting of the compressor motor and cause it to draw higher starting current longer than the fuse will allow. If that all checks out you can ohm out the compressor.
 
 

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