[neil30076]

Leo, make sure the chain is good from the duct sensor, the thermistor in back of the 'sniffer' in the right top side of the console. Open sensor in the duct as Stan indicated is the same as ( IIRC) lowest temp outside, so air will not come on - or be very minimal.
If you recall, I had the same problem and it was a broken wire behind the console that made the chain open. Symptom is also ( or wa in my case) no blower fan speeds, there is a way to test it with a 680 ohm resistor jumpered in the right place. I have the test procedure for the whole chain if you need it.