Cadillac Repair: Climate Control, dc voltmeter, jumper wire

Question
Just bought a 89 Coupe DeVille.  I noticed right off the climate control did not work.  I could hear change of modes on all the different settings, but no air, no fan, no defrost, no nothing.  The rear window defroster does work.  After I bought the car I asked the previous owner about the problem and she said she the climate control always worked for her, no problems.  I have only driven the car 100 miles and one time the fan came on for a short period of time like 1 minute.  It was on econ, auto fan set at 76 degrees.  I checked the codes and all I got was a battery disconnect code.  So no heat, no fan, no a/c, no nothing except I hear changes like clicks when changing from one mode to the other.  No change on the warmer or cooler button.

I am in the middle of our snow season and can't drive the car anyway, so a good time to work on it with your help.

Thank you

Answer
Hi Mr. Davis,

          If you get out your DC voltmeter and disconnect the blower motor connector the voltage on all fan speeds should be above 4Volts. If it is you have a defective blower motor. Most times when the motor goes out it will weaken or damage the power module which supplies the voltage to the motor. It is located in the same houseing but at the top on the passenger side and has 2 wire connectors on it. Replaceing both is the recommended fix to get the blower motor working again.

     If less than 4 volts check the fuse and the ground connection on the RF fender near the washer bottle on the 2 studs. Take them loose and useing your ohmeter determine which wire is the ground and scrape the paint from the stud area and sand the terminals alittle bit so you know they are clean and then bolt them back together. If the ground wire is good then the power module is probably defective.

     A good test to determine a blower motor that is useing too much current to work would be to unplug the power module connector that has a purple wire @ cavity A. Make a jumper wire useing 12gauge wire, a 20amp yellow fuse and a terminal to slide into terminal A at the power module connector. Hold or attach the other end of the wire to the positive battery post and if the fuse blows before 2 minuits are up then the motor is definitely bad. If the fuse doesn't blow but the motor sounds noisey like a bearing squeal or growl then the motor is still in need of replacement.

      Hope that gets the fan working again. Just remember that if you install a new motor you might be able to reuse the module. If you install a new module you have to replace the motor or the module might burn out again with-in the month. Also when testing the motor operation the module MUST be down in the houseing or it can burn out with-in 30 seconds with the motor running. Bill