DanD
April 5th, 2009, 10:03 PM
The circulating fan on my furnace will no longer come on using the constant on switch on my thermostat. A loud hum comes from the control panel in the lower section of the furnace when I switch the fan to constant on. It works fine when set to auto, both for heat and cool. It worked for years in the constant on setting and has recently failed. The furnace is an Armstrong Ultra SX 80. Any suggestions troubleshooting and repairing this would be appreciated.
