1. Your year model the default is for HEAT if the reversing valve fails. Newer Dometic they designed them to fault in cool mode if the reversing valve fails.
2. The VALVE itself is probably OK, what you have is the COIL (the 2 wires connected to it) has probably failed. When you order just the coil, Dometic sends 2 as they used 2 different types over the years and you install the one that matches your existing coil. You cannot get the actual valve as a replacement.
3. IF the valve has failed and you run more than 20 to 30 minutes and the outside ambient is over 70 degrees, you will get definite HEAT from the inside vents and after that 30 minutes the overload on the compressor will kick the compressor OFF due to overheating of the compressor. Doug