Comfortmaker not heating


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Old 12-20-09, 08:52 AM
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Comfortmaker not heating

Simply stopped working. Replaced batteries in thermostat. Nothing. Not sure where to start. Is there a troubleshooting guide. It is a 1989 gas furnance forced air model GUF175A020AIN, S#R891100039. Have tools, electric schematic and multimeter. Need direction. This is a simple system but need values for components. Thanks.
 
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Old 12-20-09, 09:20 AM
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Jump the thermostat first. Then test the control board.
 
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Old 12-20-09, 10:37 AM
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You got a good suggestion shortly after you posted.

Values: Make sure you have 120 volts coming into the furnace. The quickest way you can confirm if you have both 120 volts and 24 volts AC (not DC), is to take your multimeter set to AC volts, find the thermostat low voltage wiring terminal strip that will show connection points marked (with such letters, but not limited to...)R,W,Y,G and C, and then with your voltmeter set to AC voltage, put one probe on the R terminal and the other probe to the C terminal, and see if you get 24 votls there.

IF yes, turn up the thermostat, bypass any program on it, and see if you then get 24 volts from the W terminal to C terminal.

We can speculate after this if you give your answers.

Per Pulpos suggestion - rather than do his suggestion say at the thermostat, it is easier to bridge the terminals R and W(with some jumper wire) on that terminal strip in the furnace.
 
 

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