I tried to change out the thermostat with the digital but, when I unhooked the red and white wire from the old themostat the blower comes on and does not shut off. I hooked the new thermostat up white wire to W and red to RH and it still would not shut off until I hooked the old themostat back up. Any idea's?

Was your thermo set to heat instead of cool? A 2-wire system requires this.

It will help if we know if your trying to run heat only or cool only with the thermostat or if you have a mobile home unit that you have to manually flip a switch from heat to cool at the furnace. RH to W is for heat only.

I also have a 2-wire system on a Coleman Presidential III with a 7900-6821 A/C Blower set up on a mobile home. I manually flip a switch from heat to cool at the furnace. Does my setup run off a relay switch instead of the 4-wire typical setup? Because my blower is running continuously as well. I've checked the contactor, a single-pole, and it is fine and not stuck. I also don't see any wires touching on the t-stat. Could I have a defective relay switch? If not, what is causing this to do this?