I had an thermostat controlled outside air return added when I had A/C installed 8 years ago. 4 years ago the damper motor failed. I had the motor replaced and a switch installed so that I could turn the system off during the off season. The motor failed again last fall. When they showed up to replace the damper motor I was told that the switch would not turn off the damper motor. After 1-2 hours of replacing the motor, they pointed out as they left that the thermostat was broken and the system wasn't going to work, anyway. They admitted that they didn't know how to fix the thermostat and they didn't think the system worked well anyway. While they did reduce my bill a bit, I would have had them just disconnect the dysfunctional motor if I'd known the system was broken. I have no way to turn off the motor, but the next time it dies (~4 years???) I will pay someone else to repair or disconnect it.