My daughter lives in an old mobile home and just recently bought a new thermostat. Going from a mercury thermostat to a smart one with 4 wires. The old thermostat on top and the new Honeywell T4 Pro beneath it. On the old thermostat all my daughter had to do was move the switch from cool to heat and it would heat her trailer. Now, with the new thermostat no heat comes out. The fan blows but no heat, jusylt cold air. It's an old Coleman unit if it helps. And not sure if the jumper from the RC to 4 wire on the old thermostat may be the issue.

Thanks for any Input!

Old Mercury Thermostat

New thermostat.

 

Hi, can we assume that you have done all the programming? Check the trouble shooting section in the owners manual, also if you jump out R &W on the stat you should get heat.
Geo🇺🇸

 

Welcome to the forums.

You posted in the heat pump/electric heat forum.

Is this a gas furnace or A/C with electric heat ?
There may need to be a programming change in the stat.

 

I will look through the troubleshooting steps again and make sure the programming is correct. It is an A/C with electric heat.

 

Is the electric heat large heat strips? or from a "reverse-cycle" AC (AKA Heat-pump) the indoor coil gets hot while the outdoor one get cold the opposite of the function in cool mode. This is important as they have a reversing valve that makes it heat Vs. cool that has to be in the right direction or else you will get cold and not hot air.

 

Not enough wires for a heat pump. No O/B line
You need to program the stat for electric heat.

200 --> should be already set at 1
205 --> needs to be set for 4 - electric forced air

 

Thanks all! Reprogrammed the thermostat and now it blows heat. Of course it had to be something simple and I completely missed it. Again, thanks for everyone's help!