I have an older coleman furnace model 7670. Aprox. 7 years ago I had a new air cond unit installed. Until recently I had not tried to use the heater. The air works fine. I called a repair person in to fix the heater it would not come on. They replaced the thermostat. Now I have heat but the air won't come on. I get one or the other not both. The heating guy was baffled gave me a reduced price and told me to contact someone else.

Wow, I think that if this repair guy new what he was do-n he should have been able to fix it an know why it would be do-n this. Have you tried to contact the manufacture an ask the to see if they could may-b help you?

I got to thinking about your response and another article posted by the heat pump person with no heat only air. The repair person replaced the termostat with one similar to the thermostat that was already on there, the heat didn't work then either. I watched him install the thermostat and there are two wires left over one is blue one is black. I hear there are one state and two stage thermostats but I don't know what that means. Do you think maybe he got the wrong thermostat? Why would I have left over wires coming from the unit up to the thermostat. The old thermostat previously installed also could have been wrong and maybe that was why the heat didn't work then either (it was installed by my now ex). Does anyone have a wiring diagram for the old coleman furnace?

You have a two wire system that takes a simple thermostat if your unit is in a mobile home. The newer thermostats will not work with that design. Now if it is not in a mobile home then it could be something else.