Air handler blows 3A fuse


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Old 03-18-18, 09:45 AM
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Air handler blows 3A fuse

Lennox air handler blows 3A fuse when energizing. I awoke to a blank Honeywell TH5220D1029 thermostat this morning. I discovered this blown fuse in the Lennox CBX27UH-036-230-6-02 air handler. I removed the thermostat cover, removed the quick disconnect for the heat pump outside (Lennox XP14-036-230-10), disconnected power with both circuit breakers (1-30A, 1-60A) on the air handler and replaced the 3A fuse. When I flip on the 30A breaker the fuse blows immediately. All the low voltage wiring appears to be in good shape, no obvious issues.
Anyone have any ideas?
TIA!
 
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Old 03-18-18, 10:19 AM
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Welcome to the forums.

The 24vac is created at the air handler.... sent down to the thermostat..... back to the air handler and then to the condensor.

If the thermostat is off when the fuse blows then the problem is at the air handler or in the wiring to the thermostat. If the thermostat was on when the fuse blew.... most likely problem is in the wiring to the condensor or a defective contactor.

Trial and error with fuses is one way to locate the problem. The more effective way is to use an ohmmeter to check from the wiring to ground and for shorts.
 
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Old 03-18-18, 10:34 AM
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Thanks for the quick reply. I have tried something else that may help. I disconnected both red wires (one to the thermostat, the other to the condenser) reconnected the thermostat wire and thermostat itself. I now have power to the thermostat, the blower is working. Proving there is something going on with the condenser, correct? I checked those wires and connections again but see no issues.
 
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Old 03-18-18, 11:04 AM
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That would indicate a problem to the condensor or in the condensor.

If the wiring is all hooked back up and the the thermostat is OFF and the fuse doesn't blow.... it's more than likely a bad coil on the contactor.
 
 

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