I have a 1997 model Coleman Evcon heat pump. It has worked fine for the last 13 years, up until this summer when I set it to "cool". Hot air blew out and cooked my house until I turned it off. I replaced the thermostat thinking it finally gave out, but the system still did the same with the new thermostat. With no funds for a repairman, I left it off for the summer. Now that is getting cold again, I turned the system back on and set it to "heat", but nothing happens. You can hear the reversing valve tick on and off once in a while, but that's it.
I opened up the system and ran some tests. With the system in "heat", if I hold down the "test" button the output from the condenser turns ice cold and frosts over, and the inside heat exchanger blows ice cold air. With the same set up, if I disconnect the control signal to the reversing valve and hold "test" again, the output is screaming hot, with hot air coming out of the inside heat exchanger. If I set the system to "cool", I get no voltage at the reversing valve solenoid connector, so pushing test only results in hot pipes and air.
Additional tests: 24 volts AC at the reversing valve solenoid (when in "heat"), 16-20 ohm's across the solenoid. Low pressure connection has 150# with system idle and 110# with system in "test".

It seems to me the reversing valve is working, the compressor is working, and the whole system works just fine (able to heat and cool) if only testing, but automatic controls are not functioning. I re-verified the wiring to the thermostat (twice). Any Ideas?