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kdljet 03-05-2009 06:50 PM

Carrier Control Board Fuse Blows
I have a Carrier Heat pump with electric heat strips to supplement. Two nights ago the heat went off during the night and I woke up to fifty some degrees in the morning (normally it would not cool off that much here, but we just had that cold snap so it was about 28 degrees outside). I noted that the Thermostat was blank, but had to leave for work. After work I took the cover off the airhandler and found that the 5 amp fuse on the control board was blown. I replaced the fuse and it ran till the house was warm, it ran several times during the evening. At bedtime I noticed that it was getting cool in the house and sure enough the Themostat was blank again. I replaced the fuse again and it blew within five minutes.

After work today, it checked all of the thermostat wires (both to the thermo and to the heat pump) for shorts and found none. I pulled the plug at the heat pump and put a new fuse in then turned the thermostat to EMRHT and it seems to be working now. It has been about 3 hours and the furnace has run several times.

What is the next step? I guess I'll plug the heatpump back in tomorro evening and see what happens. If the fuse blows again is there something I can check or is it time for a new control board?


Plumber101 03-05-2009 07:41 PM

Does you condenser outside have a disconnect?

If so turn power off to the condenser. Then set your stat as if it is still in operation and see if it blows. Now just disconnecting power does not do a thing except makes it safer for you. If the fuse blows the remove the access panel on the condenser and find the contactor. This is were the power is transfered to the compressor. (That is why we turned off power) Also there will be two small wire on on each side. Remove one and make sure that it does not touch and metal because this will make the fuse blow as well.

If after a short period the fuse does not blow replace the contactor. I have seen many contactors the have an intermit internal short.

Please, if you feel a little iffy doing this then PLEASE call a pro.

High power can and will knock you on your butt if not kill you. Please use care.

kdljet 03-06-2009 04:38 PM

I already had the power to the compressor off. Decided to check the pins on the compressor control board where the thermostat plugs in for grounds before putting the plug back on. The yellow pin was shorted to ground. There is a yellow wire connected to the board opposite the yellow thermostat pin so I decided to remove it and check for grounds. The short to ground went away and did not return. I installed the thermostat plug at the compressor control board and the fuse did not blow. Everything seemed to be normal for a few minutes then I notice smoke pouring out of the thermostat. One of the transistors cooked. I'm going to get a new thermostat and see what happens next....

Plumber101 03-06-2009 05:49 PM

Showing off are you..Using that ol smoke test

kenmac 03-06-2009 08:37 PM


Originally Posted by Plumber101 (Post 241136)
Showing off are you..Using that ol smoke test

It happens to the best of us at times:laughing:

kdljet 03-11-2009 09:20 PM

OK I'm back. Recieved and installed my new thermostat. The fuse still blows when the thermostat plug on the compressor control board is connected. I pulled the plug that goes to the contactor relay with the thermostat plug installed and the fuse still blew. It sure is looking like a compressor control board unless someone can suggest another test? By the way the compressor is a Bryant model 637GJ048-A.

Thanks for the help!

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