We were waken up by the cold and found out that the furnance is not running. The furnance is a TempStar. So I did some testing
1. On the thermostat I put the fan switch from Auto to On. The fan comes on.
2. I set the thermostat to heat and hold the temperature to way above room temperature, the system on indicator is on on the thermostat.
3. I open the furnance, override the door open safety switch.
4. There is 24V ac across C and R and C and W
But nothing is running. If my memory is right, I think the exhaust motor should start running when the thermostat calls for heat.
I did a very quick test with the exhaust motor. I switch the power off to the furnance, disconnect the wire going to the motor and give it 110V. the motor turns. I donlt want to run into any risk because I donlt know what happen with just the motor running. So I disconnect the 100V as soon as I saaw the motor runs and reconnect the motor back to the furnance network.
I read some forum entry that the exhaust motor is also controlled by the pressure switch is is open at this time. But I am not sure if the pressure switch actually controls the motor when the thermostat first call for heat or it controls it after it is started first to create a pressure. Can some one confirm ? Is there a good way to test the switch if it can be the cause of the problem?