We have a brand new heat pump system, Trane XL16i heatpump with Trane variable speed airhandler (4TEE3F40A1000AB--the guys who work on it refer to it as "the 40"), Aprilaire humidifier and programable thermostate.

Approx ten days ago, as heat pump was in recovery stage moving from sleep to wake mode (60 to 68 degrees), air handler/blower began switching on and off, but would work fine if we switched to emergency heat. Thermostat would "buzz." Installer replaced the circuit board.

Everything worked fine for one week, then same problem at same time, but this time air handler would click on and off without blowing any air at all. Again the buzzing with the thermostat. After hour, hour and half, could run on emergency heat for short periods of time before problem started again. This time they replaced the "module" (modulator?) on the motor.

Worked fine for three days, then same problem, except no blower action at all, even on emergency heat. They swapped out circuit board again--no improvement.

Service guy is stumped and is calling Trane tomorrow. Has anybody else run into this? He said he's never seen this before. These guys are good and have been very responsive to service calls. They just seem quite perplexed.

In the meantime, he hotwired a regular blower motor (ie., not variable speed), so it bypasses cicuit board and is running all the time. A temporary measure to give us heat.