Expert: Roland Finston - 9/28/2011

Question
QUESTION: 1997 Chrysler LHS
Heater fan stuck on high.  The only way to shut it off is by pulling the fuse. (it does shut off when engine switch is off).  This car does have the automatic temperature control option. sm8

ANSWER: Hi Bob,
The blower module is blown. It provides the 14 different possible fan speeds, but when it goes out only high (12v) is supplied and can't be turned off. Remove the underpanel edge of the dash on the passenger side to get a good view of the under side of the HVAC unit. Then notice the round blower motor undercover at the far right end. Follow the blower motor wire to the location of the module which is held in place by 2 screws along with the plug. Remove them and the module drops out of the ductwork for replacement. You might find one at a wrecking yard where any LH-body vehicle of this general vintage and with atc control will use the same solid state module.
Roland

---------- FOLLOW-UP ----------

QUESTION: Roland: Is the module you refer too also called the resister. Thanks for the very promt reply, your answere was very helpfull.

Answer
Hi Bob,
The conventional unit with 4 speeds has a similar device called the 'resistor block' and is located similarly. But the larger number of fan speeds offered in the ATC unit resulted in the 'blower module' unit you have that has transistors/capacitors and some resistors. Thus these are not interchangeable. You could remove the old one and look for some wet spots on the circuit board underneath the electrolytic capacitors, which show a blown capacitor, which if replaced might effectively repair yours.
You are welcome. Please rate my answer and consider responding 'yes' to the question about a nomination for me to be recognized as 'volunteer of the month'. Thank you.
Roland