I just had my HVAC system inspected by a local contractor and after he left today (friday) the air handler is constantly blowing, whether the thermostat has fan set on "auto" or "on". The hander is a Lennox CB30M-65-1P connected to a heat pump, Lennox HP26-060-9P. I also tested each system state with fan set at each setting and have varied the temperature to ensure that the thermostat, a fairly new Chronotherm IV, passed the signal for the system and fan to turn on. It was the mildest day in Georgia you could ask for, so I don't think external conditions had much to do with this. I am fairly good at working with machines, being an engineer, but the handler is in the crawl-space under the house and I can't stay down there long enough to make any progress. The contracting firm is out for the weekend, and I don't really want to leave this thing blowing constantly all weekend or have to toggle the breaker whenever I think the heat pumnp has enough time to warm the house by evening.

If there is a HVAC technician "trick" to setting the fan to constant on, please let me know how to reverse it.

Thanks

I would say more likely the relay stuck when he turned it on. Track down the relay and give it a whap with a screw driver handle. If that fixes the problem, replace it. Trouble is, the newer ones are on an expensive circuit board. There is a time delay switch too that keeps the fan on for 90 seconds after the compressor shuts off. Another good suspect.