He says I need a whole new rewiring of my system. I have a mobile home furnace and a/c system that has a two wire control circuit. He says that it will never run like that and wants to sell me something similar to an Evcon 7900A6041 and rewire the whole system to 4 wires for a big price. I thought the box I had had a reversing relay and worked fine with the existing thermostat? The box I have has two switches. One is for heat and cool and the other is for auto and continuous. Its the stock switch that came with the Coleman Presidential 7600 furnace. When I disconnect the thermostat and the wires are not touching the a/c runs continuously until the heat switch is flipped.