Trane XR80 Furnace.

[Molda]

I have a Trane XR 80 furnace and need a little help. When the thermostat call for heat the indoor fan comes on instantly and run the entire cycle. Even after the temperature is satisfied Have to manually start and shutoff from the thermostat. Everything else seemed to be functioning...inductor fan, pressure switch, limit switch, flame sensor and flame ignitor.. In A/C mode fan cycles system operates normally.
Any help will be greatly appreciated..


Thanks,

Molda

[jnaas2]

First you say fan comes on instantly then you say you have to manually turn it on and off which one is it and what style thermostat and has it been changed lately

[Molda]

I only operate the furnace in manual mode ie, turning the furnace on or off manually. The indoor fan does not shutoff and runs even after the set temperature. I observed this last spring and only in the heating mode. The A/C operation cycled fine. Everything else is functioning except the fan comes on immediately as the unit is turned on and stays on.
I have a White-Rogers model#1f80-261 thermostat for over 10 years.

[jnaas2]

Most furnaces turn the fan on by the circuit board when in the heating mode because of the delay at start and at the end of the cycle, On ac it usually comes on as soon as there is a call for a/c, Make sure the fan switch is set to auto first and if it still runs all the time disconnect the green wire at thermostat and see if the fan functions correctly, There should only be a delay of around 30 seconds after the burners light if longer shut it off because the board is probably bad. One other thing, Programmable thermostats can be set up to control the fan in heat mode instead of the circuit board and your thermostat could be bad and is stuck in the on setting for fan, as long as the gas shuts off when set temperature is reached there is no problem letting the fan run some people do to help keep even temperature in there home

[Molda]

Most furnaces turn the fan on by the circuit board when in the heating mode because of the delay at start and at the end of the cycle, On ac it usually comes on as soon as there is a call for a/c, Make sure the fan switch is set to auto first and if it still runs all the time disconnect the green wire at thermostat and see if the fan functions correctly, There should only be a delay of around 30 seconds after the burners light if longer shut it off because the board is probably bad. One other thing, Programmable thermostats can be set up to control the fan in heat mode instead of the circuit board and your thermostat could be bad and is stuck in the on setting for fan, as long as the gas shuts off when set temperature is reached there is no problem letting the fan run some people do to help keep even temperature in there home

Thank you for your help. The board was bad..Very appreciative.