On May 16, 7:14*pm, Tony Hwang wrote:
randallbrink wrote:
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.

Hi,
Model of outside unit, furnace inside and your thermostat?
Do you have a multimeter? How many wires are on the 'stat.
When you are calling for cooling, you should see 24V AC between
terminals on the 'stat R and G and again between R and Y(since outside
fan runs you must see 24V AC here) If you don't see 24V AC between R and
G 'stat is bad.

I'll do this test. However, the same problem has re-occured after
replacing the thermostat. I can, however, access the wiring with the
system in operation.

It sounds like a wiring problem somewhere. You already confirmed the
fan and compressor are working, which is good. You just need to
confirm if the wiring is correct. If it is, it could be a defective
circuit board on your A/C unit.