TruAir Thermostat Problems?

[stevesherard]

I am having a problem with either my TruAir thermostat (6535B335*) or my Suburban (SH-42 2346A) furnace. The motorhome is a 2008 Itasca Suncruiser and has the basement unit Coleman heat pump (6535-871) The blower on the gas furnace came on and will not shut off and is blowing cold air through the interior heating vents and also the exterior gas exhaust vent. Every 2-3 minutes it stops for about 1/2 second then cycles right back on. The system seems to be trying to start the Suburban furnace. The TruAir thermostat switch is set to off and the fan mode is on auto. When the shore power is disconnected the blower times out and stops. I opened up the thermostat and was able to get to the wiring that goes to and from the Suburban furnace and checked the voltage. With the shore power disconnected I am reading 7 volts DC on the switch leg from the thermostat to the Suburban furnace. (blower not running) When the shore power is reconnected the voltage on the switch leg from the thermostat jumps up to 12.6 volts DC. (blower starts running) If I am analyzing this problem correctly it appears to me that I am getting a voltage bleed through on the contacts of the thermostat even when it is in the off position. Apparently when the shore power is connected there is a boost to the batteries which allows enough bleed through on the thermostat contacts to start the Suburban furnace blower? I have temporarily disconnected the power from the DC circuit breaker for the Suburban furnace to stop the blower. I am told that the TruAir thermostats cost over $300 and hate to spend the money for a replacement if this is not my problem. Any help you can provide in troubleshooting this problem would be appreciated.

[Sammie]

Sounds to me like your thermostat is junk. Can you first shut down all power, 12 volt and 110 ac. Then remove the screws holding the thermostat to the wall. Next unplug the wiring connector from the thermostat. Now restore all power and see if your blower stops running. If it does, my money is on replacing the thermostat.

Now, who told you the thermostats cost $300? I'm pretty sure you can get one for $200 or less.

Sammie