When that happens on a Chrysler Town and Country with auto temperature, the blower motor power module has failed. It is also called a blower motor resistor.
If it will only run on fast, or it won't go on in fast position. It most likely the blower motor resistor. Blower motor is OK because it is running even if it is one speed..replace the resistor. It only coast 20 - 30$
Probably the blower motor, wiring to it or control switch
Its controlled by a vacuum hose
I have the same problem with a 1991 DeVille that I acquired three days ago. The blower worked fine at first, then would not shut off but would vary speed from the dash control. Now it only runs at high speed in the off position. After shutting off the car, the dampers repositions to the heating position from the cooling position. the blower motor has a high amp draw shorting the control module, replace them both!!!!
it needs a blower motor control module located under the glove box
check the fueses check fueses
I had the same problem and ended up replacing the blower resistor and the blower motor. Although it could be one or the other .. mine was both.
There is a Blower Motor Resistor Pack. Either the blower motor speed control switch itself is defective or the Resistor Pack is bad.
Check your servos.
No only the blower.
Defective blower motor, blower motor resistor pack, or blower motor speed control switch.
Bad blower resistor?