Blower will not shut off.

[Stumped]

The blower on my HVAC system continuously runs, even when I turn the system off. I have a Trane XE78 furnace with a White Rodgers 50A50-405 controller. Any ideas on what's wrong?

[HayZee518]

see if the plenum hi limit switch is ON. there is a white button that is pulled out for continuous fan run. pushing the button IN allows for controlled operation.

[HayZee518]

The White Rodgers 50A50-405 control module is for heat only. It has a preset purge cycle for the burner, so it shouldn't affect the fan operation. Look into the circuit for fan operation. look on the print, it should tell you.

[LazyPup]

Check the fan relay to see if the NO(normally open) contacts are stuck in the NC(Normally closed) position.

[hvacwiz]

more than likely the fan reley is sticking on the furnace circuit board, if this is the case you will need to replace the entire board, the releys are not interchangeable

[Stumped]

Thanks for the advice guys. Unfortunately the only available button of any type is the kill switch for when you take the cover off. Looks like I'll have to replace the White Rodgers control module after all. Yes the module is mainly for heat but it also controlls the fan when the system is set to ac.