[JohnCurry555]

Hi everybody. Got a hopefully small problem with my heat at home, and I'm hoping somebody can give me a hand.

My thermostat is a Trane XR401, connected up to a Trane outdoor unit, and both were new and professionally installed last April. The heat and A/C both work fine.

However, this winter the fan has occasionally switched on (even though it's turned off), and it'll blow some super cold air around the house. For example, say the thermostat's set at 65 overnight. It'll keep it there until I wake up and put it to 70 or so, and it will heat the house fine to 70. So, the internal temp reads 70 on the thermostat, and the system shuts off. All groovy. But then, 20 minutes later, the fan will turn on (even though it doesn't read fan "on" on the display) and blow some cold air around, until eventually the heat will kick back in to bring the temp back up.

My thermostat only offers fan ON and fan OFF, no fan AUTO. So, any ideas what's going on? Thanks for any and all help!

[hvac1000]

There is a sensor OR a item sometimes called a fan control that operates the units fan during the heating cycle. If this item is out of adjustment or needs to be replaced you will sometimes experience phantom blower operation. In a nut shell this is caused by residual heat left in the heat exchange area after the blower first turns off. This heat can build up after a short time and activate the blower motor again.

Another possibility is the blower is operated by an electronic timer device. If this is defective it can also allow phantom blower cycles. Unless you have the knowledge and the proper tools these faults can be difficult to find and a on site visit from your local HVAC company might be the way to go unless you feel qualified to do it yourself.

[johnair77]

Primary or secondary limit opening maybe?

[JohnCurry555]

Thanks for the responses