I have a puzzling problem. When I select "Cool" on my thermostat, the central fan does not come on, and so, while the air conditioner outside runs, it quickly freezes, as there is no air movement. On the other hand, if I select the heat-cool switch to "Off" and turn the fan "On" the fan works fine. But if while the fan is running, I move the Heat-Cool switch to "Cool" the fan shuts off. I have replace the thermostat, and have the same problem.
Any help will be greatly appreciated, as the outdoor temperature is now 90F.