Have a coleman 7900 gas fired heat/cool unit in mobile home. Just installed Honeywell wifi thermostat. I only have 4 wires to t stat. they told me to move the G wire to common on both ends and it will work. Heat works OK but when in cooling mode , compressor comes on but fan does not. The wi fi requires a common wire at the t-stat. If I run a wire (temporarily) from the common side of the 24vac xfmr to the C terminal on the t-stat(and leave the G wire in the G terminal on the stat) everything works fine. Any suggestions without having to do major work and pull in new wires. Honeywell can't helpl

Sorry, but you are going to have to pull another wire, or at this point pull a five wire stat cable. With your stat, and having heat and a/c, you need a five wire cable. There are some products out there that say they can make a four wire into a five wire, but I have not seen, nor dealt with them. If you are interested, look into "venstar Add a Wire". May be just what you are looking for. The wiring is pretty straight forward as long as you can interpret the wiring diagram and instructions.