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Old 06-05-2010, 03:40 PM   #1
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replaced thermostat....nothing, need help please


My thermostat melted the other night, I replaced it, the furnace and fan would work but not A/C. Now nothing works.

I have power going to the unit in the basement from the heat side and the A/C side (from the circuit box). I have power at the AC unit outside. Where do I begin? Is the main circuit board the culprit? When I had a problem previously with the furnace, an indicator light was functioning, but now nothing is. I only see 1 fuse on the unit and that is on the heat side, fuse is good and there is power on both sides.

I am good around the house, but don't know where to start here? Circuit board is $150 or so, how do I troubleshoot this? I'm hoping its just a relay somewhere I'm missing.

Thanks

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Old 06-05-2010, 03:53 PM   #2
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replaced thermostat....nothing, need help please


Why did the tstat melt? Did you have a thunderstorm/power surge/lightning? Post the make and model # of the furnace and some pics of it. Click on Go Advanced.

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Old 06-05-2010, 04:03 PM   #3
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replaced thermostat....nothing, need help please


No thunderstorm. No tripped breakers/blown fuses. It is amana air command 95 furnace and amana AC.
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Old 06-05-2010, 04:19 PM   #4
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replaced thermostat....nothing, need help please


You should get 24 volts between R and C terminals on the circuit board. What literally happened to the tstat/melted?
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Old 06-05-2010, 04:35 PM   #5
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replaced thermostat....nothing, need help please


I just did this

ran blower wire to direct power (around circuit board) and the blower motor ran fine.
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Old 06-05-2010, 04:46 PM   #6
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replaced thermostat....nothing, need help please


The thermostat melted a hole in the back. I don't know if the wires touched and arced or what? Right now I have the fan running by bypassing the circuit board. I can replace the circuit board, I just want to know if I can possibly test other switches/controls to replace them and not the entire board. Also, how can I ensure that the same problem won't happen again?
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Old 06-05-2010, 05:05 PM   #7
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replaced thermostat....nothing, need help please


Do you have 24 volts between R and C, follow our instructions carefully we are Pros.
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Last edited by yuri; 06-05-2010 at 06:49 PM.
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Old 06-05-2010, 05:06 PM   #8
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replaced thermostat....nothing, need help please


at the thermostat or on the circuit board? I have to find my multimeter and will check
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Old 06-05-2010, 05:31 PM   #9
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replaced thermostat....nothing, need help please


At the circuit board.
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Old 06-05-2010, 05:31 PM   #10
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replaced thermostat....nothing, need help please


never heard of a stat melting on a wall. if you jumper y
to r do you get cooling or jumper r to w do you get heat r to g should give you fan. on some furnaces no ground to unit will fry board did you check transformer for 110 on line side and 24 volts on low side?
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Old 06-05-2010, 05:47 PM   #11
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replaced thermostat....nothing, need help please


Unhook t-stat from control board
Makesure you have 24 volts @r&c
jumper r-g=fan should come on
" r-w=heat"""""""""""""""""
" r-y=cond."""""""""""""""""for cond. to work cond common needs to be hooked up and pump or pan safety switchs need to be closed or bypassed"
I take it you already have high voltage since you got the fan going but it never hurts to make sure its the right voltage
If you have high&low voltage and none of the jumpers worked then it looks like the board

BTW If your t-stat melted there is a good chance your t-stat wire is shot too.
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Old 06-05-2010, 05:53 PM   #12
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replaced thermostat....nothing, need help please


just tested R and C at the thermostat and on the board. no voltage.
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Old 06-05-2010, 06:12 PM   #13
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replaced thermostat....nothing, need help please


Now check the transformer and make sure if the furnace has a fuse on the control board that it is good too.
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Old 06-05-2010, 06:15 PM   #14
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replaced thermostat....nothing, need help please


I have no power from where my AC low voltage connects in with the high power.
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Old 06-05-2010, 06:30 PM   #15
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replaced thermostat....nothing, need help please


Does your blower door have a kill switch?
High voltage shoulg go through an on/off switch through the blower door kill switch then to control board and t-fromer.
Test high voltage at all 3 places, if thumbs up then sounds like bad t-former but ohm it out to be sure.

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