Coleman Presidential III Model # 7970A856 Furnace.

[civiccrazy]

The furnace runs for 1-2 minutes, then shuts off for about 30 seconds to a minute, then comes back on. It does that until it gets to the temp i set the thermostat to. I called the local technician, he said it was the fan Switch. He said check the voltage going to the fan switch. (I will attach pics) I checked the voltage going to both the little brown disks he told me that one of them was the fan switch. Both disks showed it had power to all the wires while the furance was running. I turned the thermostat down to where the funace would shut off and I checked it again. The disk on the right had power to all 3 wires while it was off. The disk on the left, the top wire had no power and the bottom did. The disk on the left was the one that i thought was the fan switch according to the diagram on the cover.

[Robert]

Yes, the one on the left should be the fan switch.



Thanks,
Robert

[civiccrazy]

ok, should both of the wires have power when its running and the top wire have no power and the bottom one have power when the furnace is not running?

[Robert]

Both wires to ground should read 120vac when running. When off, input wire to ground should read 120vac and output wire should read 0vac.




Thanks,
Robert

[civiccrazy]

The furnace is stilll doing the same thing, could it be the fan switch?? If so, how would i go about ordering one?

[Robert]

Hi,

Did you test it as suggested in last reply ?


Thanks,
Robert

[civiccrazy]

Yes I did, Both wires to ground read 120vac when running. When off, the bottom wire to ground read 120vac and the top wire read 0vac.

If Thats not whats wrong with it what else could it be?

[civiccrazy]

Tonight the fan motor started sqeaking really loud. Is there anything I can do to stop that or do i have to buy a new fan motor.

[Robert]

Trace motor lead back to closest connection and see if it is getting full power when the motor stops.


Check for manual oil ports on motor.



Thanks,
Robert

[civiccrazy]

I'm sorry. I am not getting what you are saying about tracing the motor lead back to closest connection?


I am also trying to figure out whats wrong on the ask me help desk. Someone else said:
It sounds like all along that the problem was in the motor, it has an internal heat protector and when it would run for 30 seconds and cut off it was the internal switch that was cutting off the motor.

The reason I believe this is because the motor is now squeking, that probably means that the bearings in the motor are either dry or they are worn out.

Could the motor be going bad? Causing all this trouble?

[Robert]

Hi,

Trace the motor power lead back to molex plug, wire nut or whatever it connects to and see if it has full 120vac power at that point.



Could motor be bad, yes. Did you look for oil ports ?

When it cuts off, is it hot ?




Thanks,
Robert

[civiccrazy]

I traced the wire from the motor to the control box underneath. It had 120vac power. When it cuts off it is not hot.

I had someone come out and look at it today. Two switches were bad....the one that switches it from AC to Heat, and the one on the little box below that which i think is the power switch. I asked him about the motor, and the whole time he was here looking at it with it running is ran fine no sqeaking or anything.

[Robert]

Hi,

One question you may want to think about is IF those switches were bad, how did you have 120vac at the motor lead ?


Also, how was it running ? Did the motor ever stop and the switches show bad meaning an intermittant problem ?



Thanks,
Robert

[civiccrazy]

the motor never stopped just squeaked for a little bit. I will keep a close eye on it. If I starts squeaking again i will replace the motor