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Old 05-31-2010, 01:08 AM   #1
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thermostat melted...


Have older amana AC/gas furnace, woke up after running AC for first time this summer to a burnt plastic smell to discover the thermostat with a hole burned in it. I replace the thermostat and heat and fan would work but not AC, after rearranging my wires to make sure it was wired correctly I now have nothing working, not heat, not AC, not fan. Where do I start to diagnose this? I have checked the breaker and the fuse on the side of the furnace. I'm handy around the house but have little heat/AC experience.

Thanks for any help.

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Old 05-31-2010, 09:05 AM   #2
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thermostat melted...


sounds like the contactor within the condenser section burnt up..go outside shut the disconnect and pop the control cover..see if you smell burnt like air..remove the 2 thin low voltage wires tape them away for now....remove stat from subbase.jump R to G (FAN ON) to verify you have your 24V control power from the furnace..?if you see or smell burnt out in the control contactor that short went right thru the stat causing the meltdown...if it was the first start could of been rust or even a bug sleeping in the coil and when it didn't pull in true it drew on the transformer melting the stat...at least you didn't lose the TR if that fan works on the jump...paper clip is cool for a jump to just bump it.new contactor 24V coil one pole can get at your local Grainger they welcome home owners....#5B133 on the grainger site.see if it pushes in maually with disconnect off.did you feel cooling before the meltdown..if the compressor shorted out the contactors should show major carbon burn flash black around the contacts... if they are somewhat copper clean probably the coil shorted as i said above....you don't need the condenser disconnect on to check the 24Vs from the furnace and stat call after repair just connect the taped off wires and it should pul in if the stat is calling ...won't get the compressor bouncing on with the main power off...get back with any questions...

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Old 05-31-2010, 10:15 AM   #3
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thermostat melted...


I've seen a 24 volt thermostat melt before. In that case, the start capacitor blew it's top and shorted to the 5 minute time delay relay. The stat wire was toasted as well.

I pulled new stat wire from the furnace to the thermostat and outdoor unit, replaced the contactor, time delay relay and start kit outside, replaced the fan center in the old furnace, and replaced the thermostat on that Halloween night beeper call.

I hope your damage is not as bad. If Grainger turns you away, you can try a few other wholesalers in your area.

Last edited by Houston204; 05-31-2010 at 10:30 AM. Reason: spelling
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