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Discussion Starter · #1 ·
The low voltage thermostat wire from a condensor unit outside to the thermostat control board above the air handler unit appears to be shorting and blowing the transformer. I installed an inline fuse to protect the transformer and ran a jumper wire from the control board to directly to the condensor unit. The Unit ran for 2 days with no problems, never blowing the fuse. This seemed to verify that there was a short somewhere in that existing wire (the house is 20 yrs old)....Instead of running all new wire, I decided to reconnect the existing wire at the condensor unit and look for evidence of bad wire in the attic (at least for the wire I could see). I went back as far as I could get to and spliced into the existing wire in the attic and ran new wire to the thermostat control board.... The unit ran fine for 1 night, in the morning the fuse was blown. I understand the basics of system components. Does the fact that unit ran for 2 days with no problems tell me that I need to replace the entire wire? Why did the unit run for 1 night with the short jumper? All the connections look good. I am hoping for any suggestions or insight on what to check next.
 

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Discussion Starter · #3 ·
I believe its the cable (wire) because when I ran the new 200 ft wire from the attic down the stairs and out the window to the unit, it ran for 2 days without blowing the fuse. Considered leaving the wire for a few days to confirm, but the wife would not go for that more than a 2 days. Thats why I went back up in the attic and made the splice back as far as I could physically get to.
 
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