Thermostat Melted... - HVAC - DIY Chatroom Home Improvement Forum

Go Back   DIY Chatroom Home Improvement Forum > Home Improvement > HVAC


Thread Tools Display Modes
Old 05-31-2010, 12:08 AM   #1
Join Date: May 2010
Posts: 10
Rewards Points: 10

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.


diywhy is offline   Reply With Quote
Old 05-31-2010, 08:05 AM   #2
biggles's Avatar
Join Date: Jan 2008
Location: Long Island
Posts: 3,630
Rewards Points: 2,000

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 least you didn't lose the TR if that fan works on the jump...paper clip is cool for a jump to just bump 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 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...


biggles is offline   Reply With Quote
Old 05-31-2010, 09:15 AM   #3
Houston204's Avatar
Join Date: Oct 2009
Location: Houston, Texas
Posts: 615
Rewards Points: 556

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 09:30 AM. Reason: spelling
Houston204 is offline   Reply With Quote

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off

Similar Threads
Thread Thread Starter Forum Replies Last Post
Carrier Edge Thermostat Installation Issue ptalar HVAC 1 07-13-2010 05:40 PM
Problem with Lennox Pulse Furnace Wiring to Thermostat scalvin Electrical 4 12-30-2009 07:48 PM
Two Wire 24V Thermostat to Digital Thermostat on Pellet Stove jrodtaclet Electrical 4 09-15-2009 05:37 PM
Replacing thermostat...................... sktn77a HVAC 6 09-02-2009 10:07 PM
Thermostat from Manual to Digital trinamillersmit HVAC 5 07-02-2009 09:21 AM

Top of Page | View New Posts


Search Engine Friendly URLs by vBSEO 3.6.1