5 Amp Fuse Blowing

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5 Amp Fuse Blowing

Post by Gator2222 » Tue Jun 07, 2016 12:00 am

I bought a condo around 10 years ago. The HVAC unit was pretty new at the time. I installed a new programmable thermostat as soon as I moved in.

Recently, the AC was not working and the thermostat display was blank. I traced the problem back to a blown 5 amp fuse in the air handler. I replaced the fuse and waited for it to blow again, but it just kept working. I went to bed and awoke the next morning to find the fuse had blown again. When I returned home from work I put a new fuse in and prepared to trace the problem down. This time the fuse blew as soon as I put the air handler disconnect back in place.

I went to the outside unit and took the service cover off. The contactor looked pitted. I took pictures of the contactor and the wires so I would be able to replace them as they were. I took the contactor off the unit and went to the local parts store. They sold me a new contactor and I put it on the unit.

Once again, as soon as I put the disconnects back in place the fuse blew. I was able to get power to the thermostat briefly (it runs on the 24v and does not require batteries). It simply said replace. I took pictures of the wiring and bought a new thermostat. This time the fuse did not blow when I put the disconnects back, but it did blow as soon as I put the thermostat in place. It also blew immediately if the thermostat was already in place when I put the disconnects back in place.

I am getting 24 volts between the red and all other wires. If I jump the red and the yellow the outside unit powers on and the fuse does not blow. If I jump the red and the green the air handler powers up and the fuse does not blow. If I jump the red, green, yellow and orange all together the outside unit and air handler power on and cold air is produced throughout the house and the fuse does not blow. I live in Florida and it is a bajillion degrees outside, so I have not jumped the red and the white. Going without AC is hard enough right now without turning on the heat even briefly.

To my untrained eye it seems that I must have the thermostat miswired. However, orange turns on the reversing valve, yellow turns on the outside fan, green turns on the air handler. It seems that I have everything wired correctly.

I can post all of the pictures if it is possible to do that on this forum.

The HVAC is a Carrier heat pump. The new thermostat is a Honeywell RTHL3550. The wires coming out of the wall for the thermostat are white, yellow, green, orange, red and blue. The blue is not connected and is taped off. All of the other wires are connected to the corresponding color with white as Aux and jumpered to E. R and RC are jumpered to each other as well.

I don't know what to do next. Any help is greatly appreciated.

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- 5 Amp Fuse Blowing

Post by Freon » Tue Jun 21, 2016 4:22 pm

Make and model of the thermostat? How long did everything work after you installed this new programmable thermostat?

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