80's Carrier Furnace Problem

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Old 11-27-16, 11:20 AM
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80's Carrier Furnace Problem

Carrier Model: 58SSB80-CC

Turned on furnace yesterday before I left and set thermostat to 70 and was working fine, no other programming was set to turn it off. Returned 3 hours later, furnace was off and it was 63 degrees in my house. Checked thermostat setting and it was still set to 70. Blower motor will turn on when AC is activated and works fine. Blower motor will also turn on when set to Heat and switched from Auto to On.

I pulled the cover off of my control panel and checked the relay and it is working fine. I cannot find an electrical schematic anywhere so I am turning to you guys. Where should I go from here?
 
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Old 11-27-16, 02:12 PM
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https://www.manualguru.com/carrier/5...-manual/page-4

A circuit diagram for your furnace is above. You may want to print that out and tape it to the inside of the blower compartment door, where it belongs.


You furnace has a Carrier three wire pilot ignition system with an inducer motor and pressure switch.

There are two "blower motors." the one that is turning on circulates air around the house. A small blower motor called the inducer motor is located above the burners and circulates combustion air into, through and out of the furnace.

The thermostat completes a circuit between the R and W terminals on the circuit board. When a circuit between those terminals is completed, the inducer motor should turn on and come up to speed.

You obviously have 120 VAC to the furnace to operate the fan motor.

The odds are pretty good that the thermostat isn't turning on the inducer motor. Try shorting the R and W terminals together with a piece of copper wire to see if that turns on the furnace. If so, you have a problem with the thermostat or thermostat wiring.
 
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Old 11-27-16, 02:18 PM
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Thank you! I did find out that I have 120 v going to the inducer motor and it does not turn on. Should I replace it?
 
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Old 11-27-16, 02:24 PM
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If you have confirmed 120v on the motors leads using a meter.... then the motor is bad.
 
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Old 11-27-16, 02:25 PM
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Probably.

To be thorough, remove the bolts that hold the inducer motor to the furnace chassis and pull out the inducer motor assembly.

Will the inducer motor power up when removed from the furnace? Is the fan stiff to turn? Does the motor get hot and overheat? Are the fan blades free to turn or plugged with junk?

Usually if the inducer motor is getting 120 VAC as you describe but not starting up, it would be HOT and you would have reported that.

Do you observe the 120 VAC to the inducer motor being switched on when the thermostat calls for heat?

In short, you want to use several means to verify that the motor is bad before replacing it. Nothing worse than laying out a lot of money for an expensive part and waiting to get it only to discover that something else is the problem!

Did you use a multimeter to measure the AC voltage going to the inducer motor?

Finally, if you replace the inducer motor, shop for the inducer motor assembly or kit. That includes the motor, fan, gaskets and sheet metal to attach the assembly to the furnace. That make replacement MUVH easier, and is worth spending a few extra bucks over just the motor.
 
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Old 11-27-16, 02:54 PM
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Inducer assemblies are expensive and finding one for a 30 year old furnace may be difficult.

When is the last time the furnace was professionally inspected?
 
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Old 11-27-16, 03:22 PM
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I have confirmed that there is 120v going to the motor when the heater is switched on at the thermostat. The fan blades turn freely but I have not noticed any heat and have not removed it from the furnace to see if it will work independently.
 
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Old 11-27-16, 03:56 PM
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I just tested the voltage at the motor with the thermostat off and it still reads 120v. Is this normal?
 
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