Expert: Roland Finston - 2/9/2012

Question
QUESTION: I've got a 2001 Chrysler T&C LXi with dual zone, thermostat controlled heating and cooling with 218,000 miles.  The front blower operation is intermittent at any speed.  There seems to be no pattern of when it will work and not work.  The rear blower always works at any speed. I have replaced the front blower relay (in the box under the hood) and cleaned all the connector contacts I can get to inside (blower motor resistor, blower motor connector - both behind the glove compartment).  I've also removed the center bezel and disconnected the 3 control module connectors - 2 on bottom module (HVAC), 1 on top (Heated Seats, rear wiper), and cleaned them.  When I reassembled everything, the front blower came on and I thought it was fixed.  Once I turned it off however and turned it back on, it did not come on.  I could hear all of the louvers in the ducting moving around but the blower did not come back on.  During this session, at a random time, the blower just came on - when the rotary switch was in the middle position.  I turned it back off and again, it would never come back on.  I also have a few LEDs that do not light up on the bottom and top control modules.  As a side note, ALL of the LEDs were out for at least a year of driving.  I had to replace the driver's side automatic window mechanism (including motor) and when I did, all the LEDs (save a few of them) began to work!  Any ideas on what I should do?  This is very frustrating to say the least.  Thanks!

ANSWER: Hi Dan,
When you say that the system is 'thermostatic controlled' I take that to mean it is an automatic temperature controlled system, correct? If that is the case, then you may not be aware that the blower motor is not simply controlled by a resistor block but rather by a power module which is complex electrically. Unfortunately the best way to diagnose the problem is with a sophisticated diagnostic readout box (DRB III) which is likely a dealer or other well-equpped shop instrument. I would suspect that the blower motor power module is the problem so you might want to compare the cost of that part and installing it yourself, with the labor cost of having a shop do the readout and labor, or just get a readout and then ask what the code says should be done and doing it yourself.
I have the wiring diagrams for the '02 model year ATC, but without some diagnosis with the DRB it is going to be 'throwing parts' at the problem. In this case, if the blower is reliable, it would seem to be the blower module but there is no guarantee. It might also be the cabin temp sensor, for example.
Please let me know how you work this out. I haven't received a question similar to this that I can recall.
Roland

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QUESTION: Thank you very much Roland.  Sounds like it may be the blower motor power module.  There is a shop that will probably do the diagnosis for me and give me the readout and recommended repair options.  I'll pursue that for now.  Is the install pretty straightforward?  I am very mechanically inclined (I'm a mechanical product design engineer with a large consumer porducts corp.) and have done much of my own auto work to the point of dismantling and rebuidling an engine and manual transmission.  I routinely do brakes, alternators, pulleys, belts etc.  When I get into these electrical type issues though it gets tricky.  If the install is simply finding, removing and replacing the module, I'm sure I can do it.  I'd apprecaite your thoughts though.  Thanks again and I'll let you know what the shop recommends.

Answer
Hi Dan,
Changing out the 'power module' is easy. You already did it: it is what you called the blower motor resistor, which if you have ATC is rather called the "blower motor power module". You just open the glove box, then press the sides inward, close to the top, so that the bumpers that secure it in place clear the sides of the opening, and then roll it downward and out. You will see the module is inserted into the heater/ac housing, it has a couple of screws that secure it in place. First remove the plug attached to wires that come from the blower motor, and remove the plug that comes from the AC/heat control panel. Then remove the screws and pull out the module. Install is the reverse. There is no voltage on the plugs if the ignition is off so you don't have to disconnect the battery.
You might want to compare the cost of the diagnosis to instead just buying the module and installing it and see if that solves the problem.
Roland