Carrier furnace hit with power spike


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Old 09-14-13, 07:26 PM
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Carrier furnace hit with power spike

I have a duplex with two identical Carrrier model 58GP100-2 furnaces installed in 1988. The building was hit with a power spike that left the furnace blowers running and smelling hot. The blowers in both units now run constantly. My first thought were the fan high temp switches, but they both test fine. I checked them for continuity with a tester. I am wondering if the control boards are bad. They have two relays on the control board which appear to be soldered in place as I tried to pull them of to see if the contacts are stuck.
Any thoughts?
 
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Old 09-14-13, 07:31 PM
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Welcome to the forums.

Some control boards have a protection fuse on them and when it blows the blower can remain running. The fuse could be a 3 or 5 amp and look like the plastic type car fuses.


See page 7 in the service manual in the link below for blower operation description
carrier groups public documents PDF
 
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Old 09-14-13, 07:49 PM
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Pj max,
Thanks for the document link. I am not at the rental unit now, I am going back tomorrow. I did not notice a fuse on the control board, its pretty old school. I did pull the cover that exposes the board. Would the fuse be located somewhere else. What if there is no fuse?
 
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Old 09-14-13, 07:55 PM
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If there was no fuse you would need to check for 24vac.
You said the blower runs....if you turn the heat on does anything happen ?
 
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Old 09-15-13, 09:42 AM
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OK, I went down and checked to see if the furnace fires up if I turn up the thermostat and it does not fire up. I checked the voltage before the transformer and it is getting 120v but on the output side of the transformer I am getting nothing. So I guess my next step should be to change out the transformer?

Any chance if I have these units checked by a repair guy I can get them replaced by my insurance?
 
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Old 09-16-13, 06:25 PM
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I replaced the transformer and now the fan relay works correctly and the fan does not run all the time. But the furnace does not fire when the thermostat is turned up.
Whats next?
 
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Old 09-16-13, 06:38 PM
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It could be a thermostat issue. Does your fan come on when you set the thermostat to "FAN ON"? Will the a/c come on if you place it on "COOL"? If not, then I would suggest you bypass the thermostat to see if that is the problem. You can use a jumper wire between the wires on the "R" and "W" terminals to see if the furnace will fire. I like to turn power off to the furnace, remove the thermostat from the wall and remove the wires and turn power back on to the furnace. Keep the wires separated from each other. Then touch the necessary wires together (or use a jumper or actually tie the wires together) to troubleshoot the different functions:

r to g- fan should come on
r to w-heat should come on
r to y-cool should come on
r to g to y-cool and fan should start
r to g to w-heat and fan should start

In your case, if you touch r to g to w the furnace and fan should start. If so, that would point to the thermostat being bad.

If the furnace still doesn't come on then you will need to test for proper voltage (24VAC) between the different thermostat terminals.

Sometimes it just takes a systematic approach to troubleshoot the issue.
 

Last edited by firedawgsatx; 09-16-13 at 06:59 PM.
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Old 09-16-13, 07:47 PM
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It could be a thermostat and it could be a control board issue. Hard to tell after the transformer burned out. Try firedawgs suggestions first.

You mentioned two problem furnaces...... did the other one also require a transformer and what's its status now ?
 
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Old 09-16-13, 09:23 PM
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What type of thermostat do you have? Is it battery powered or does it receive a constant 24V from the common wire from the 24V transformer. If it is a digital thermostat sometimes when the power goes off the thermostat will default to original factory settings and it will have to be re-configured again in the installer's set up menu. If the batteries are weak or go dead it can cause all kinds of problems with the system's operation. One other thing: after the power surge did you reset the breaker(s) by turning all the way on (if tripped) back off and back on again? Sometimes you will lose one leg of the line voltage. It could very well be the control board(s). Is there anything else in the house that the power surge affected? As far as insurance covering the problem that would depend on the coverage you have on your policy. I have that coverage in mine policy but sometimes the deductible is more than the replacement costs. Many years ago, myself and some other neighbors on my street all had our condensers get ruined by a power surge caused by the utility company. We filed formal complaints and the utility company agreed to pay for all costs for the replacement compressors and labor. Did any of the surrounding houses in the area have any issues with the power surge? It might pay to ask around and see what your recourse might be.
 
 

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