5 amp fuse blowing off on the inside control panel

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Old 01-18-08, 07:55 PM
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5 amp fuse blowing off on the inside control panel

I have a carrier heat pump and one day I noticed that my thermostat had gone blank. I worked my way and was able to determine that the 5 amp fuse on the control panel inside the indoor unit had blown. I replaced the fuse and the thermostat light came on again. After the "rest" period, the unit started working but the fuse blew immediately and the t-stat went blank again. I replaced the fuse again after a few minutes and this time the heat pump worked fine for a few days.

Today, the fuse blew again and I have gone through 3 fuses with no luck. On the t-stat I have 4 positions - cool, off, heat and emergency heat. I have set it to emer heat and the blower is working and the house is getting heated. Of course the outside unit is not working. The indoor unit cycles on and off to maintain the desired temperature. However, once I turn the control to heat, i.e. to operate the heat pump in the normal mode, the fuse blows up immediately. The outside unit is not iced up.

I read on some other post that suggested that it could be the defrost board or the contactor. If the unit is not iced up and the fuse blows, could it be the defrost board? How do I determine if it is. Regarding the contactor, I had replaced it 15 months ago and it is possible that it went bad again. But could someone please explain how a defective contactor would blow up the 5 amp fuse in the inside unit. I am trying to learn.

Any suggestions to resolve this would be appreciated. I am pretty handy.
 

Last edited by bharat; 01-18-08 at 08:21 PM.
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Old 01-18-08, 08:20 PM
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You have a short in your control voltage circuit here is how I try to figure it out \.

Take all the wires off the thermostat and replace the fuse if it doesn't blow then you shut of the power and tie the heat wires together (usually white green and red) if the fuse blows then you know the short is in the heating control circuit (either on the green wire,fan or the white wire,heat)
If it does not blow you can tie the cooling wires together(usually red yellow and green) if it still does not blow the problem is probably in your thermostat but going by what you have described the problem is most likely in your outdoor unit or the wire going to it so first check the control wires going to the outdoor unit (frayed or bare wires) if nothing looks bad then disconnect the control wires and turn the heat on like you did when the fuse blew previously if it does not blow then the problem is certainly in your outdoor unit probably a bare wire up against steel or a bad contactor or control board
 
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Old 01-18-08, 09:32 PM
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Mike,
Thanks for your thoughts. It is late now. Tomorrow, this is what I plan to do. Let me know what you think.
I will first do a visual inspection on the control wires both in the inside unit and the outside unit to see if any wires are bare. Next I will remove the control wire connections in the outside unit and switch the thermostat to heat. If the fuse blows, then it is probably the control board in the inside unit. If the fuse does not blow, then it is probably the contactor in the outside unit. Does this sound reasonable?
 
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Old 01-20-08, 06:32 PM
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I worked on the heat pump today and I think I have isolated the problem to the contactor in the outside unit. I have disconnected the 24 volt connection to the contactor and the fuse is working okay. Right now the outside unit is not working because the contactor is disconnected and the indoor unit is working on emergency heat.

I will change the contactor on Tuesday/Wednesday and let everyone know if the fuse is behaving.
 
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Old 02-08-08, 05:25 AM
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We are having this same problem! We have had a tech out three times and each time he can find nothing wrong with thte unit. It was the fuse blowing, thought it was fixed and now it is not working again after 4 days. No emergency heat either!

What were you solutions to the fuse.

Thanks!!
 
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Old 02-08-08, 08:27 AM
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Wink

wehave5
You have to check all the 24V wire .To the tstat to the blower and to the condenser outside and the tstat.

Like bharat came up with .It can be the wires to it or it is the contactor. Sometimes you just have to play around with it. I have had sometimes when its bugs in a relay. WHO KNOWS???
 
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