Heat coming out of air vents when HVAC system is turned off?

I have a 2007 Pontiac Grand Prix with a manual climate control system. All the functions work all the fan speeds, when I chose the vents to blow air through a certain vent they work right (floor vents, dashboard vents defrost). The temperature knob works right. But when I turn off the hvac system air blows through the vents, when the engine is cold the air coming through the vents is cool, but as the engine warms up the air coming through the vents is hot. Also I have changed the climate control interface/ controls that has the knobs to control all the functions and changed the blower motor resistor/ module. Is there any possibility of a blower motor causing this problem? Thank you for taking the time to read this, I appreciate any suggestions

Sorry for the late response! :blush:

For whatever it's worth, I've noticed other Pontiacs of this generation do the same thing. Like there's always some HVAC airflow even though you didn't ask for any. I never dug into it because none of my customers were ever complaining about it. :silly:

If you really want to know what's happening, I'd suggest checking voltages at the blower motor controller. Here's a diagram for the Manual system:



Because you report that the blower motor works on all speeds, I'm gonna figure pins A and C are fine. Pin B is what we're interested in. It's a 5V square wave signal. The blower controller provides the 5V, and the HVAC control module pulse width grounds it to get various blower speeds. No pulse width means the blower motor shouldn't turn.

A scope is not required, just a DVOM and a backprobe.