88' Bonneville SSE strange heater problem...

[boriquaking55]

Hi This is my first post here and I come to u with the strangest of problems.

Im having a pretty strange problem with my heater/climate control system. You see, about a year ago I had to replace my air compressor and rather than spend $500 on it I had it disabled instead. Well, after that I lost air conditioning and most climate control functions naturally but my heater was still operational. The car ran without problems for the whole year.

However, recently I've had a major problem with the heater. It operates alright, it just wont ever shut off. The fans continue to run regardless of whether I have my heater on or not, and continue to run even after shutting off the ignition. Its a serious problem because if I just turn the car off the fans will continue to run and if I dont do anything the battery will drain. I managed to temporarily disable it by disconnecting the line that runs the battery directly to the climate control system. This is a temp fix and I must find a way to repair it because I live in Nebraska and its December, and well, Im sane.....


Also, Ive owned my 88 Bonneville for about 4 years now and have performed regular maintanence on it for the whole period Ive owned it. The car has 120,000 miles on it, the previous owner only put 95,000 on it before i bought it. If its a minor problem like a sensor or something like that going bad, I would be greatly relieved.

Does anyone have any experience or tips for me? Any help would be appreciated.

[LMP]

I do not have the data specific to that car but most GM are the same and my reply here applies only if the blower runs at FULL SPEED.
If this is the case, the full speed - and only the full speed - is provided through a relay, and the relay contacts might just have stuck, possibly due to melting after having run at full speed for a while - this fan drains more than 25 amps. The 12V feed to the power contact of that relay is HOT at ALL TIMES, and that is why it would keep running even with key off.
IN that case, the relay has to be changed....it is normally located on the heater module, in the engine compartment, near to the blower fan motor, probably looking just about like that: www.avigex.ca/xport/heaterrelay.jpg

[randman1]

What was stated above is good advice, but if you have the Electronic Climate Control your vehicle does not have the HI fan relay. Blower motor speed is controled by a Blower Control Module located on top of the blower housing (under the hood) and can be accessed by removing the cover for the fuseable links. The BCM is controled by signals from the HVAC programmer and is a solid-state electronic device (no moving parts). A blower running even after the ignition has been turned off indicates a faulty BCM. These can be pretty pricey around $90. I got one from a junkyard to replace the one in my 93 for $25. I tried to take the one out of my 90 for testing but it was not compatible. This means you will need one from that generation (87-91). This is what it looks like:

[boriquaking55]

Thanx for the prompt replies regarding my problem. I will look into it but I have one question.

How difficult would it be to replace the BCM unit by myself? Should I just take it into the NAPA shop nearby instead and have them do it?

[randman1]

Once you get the replacement part, it's rather easy to change. Remove the fusible link cover and you'll see the blower housing. The BCM is right on top. Disconnect the electrical connector and you will see... 6 screw heads (I'm going from memory here). You want to remove only the outer ones as the inner ones fasten the heat sink to the top section. They are either 1/4" or 9/32" heads on the screws. The BCM can be a bit stubborn as the heat sink valleys like to hook onto the housing but it simply lifts out. Chuck the old one and insert the replacement, reinstall the screws and reconnect the electrical connector.

It's a one beer job.

[boriquaking55]

Originally Posted by randman1

Once you get the replacement part, it's rather easy to change. Remove the fusible link cover and you'll see the blower housing. The BCM is right on top. Disconnect the electrical connector and you will see... 6 screw heads (I'm going from memory here). You want to remove only the outer ones as the inner ones fasten the heat sink to the top section. They are either 1/4" or 9/32" heads on the screws. The BCM can be a bit stubborn as the heat sink valleys like to hook onto the housing but it simply lifts out. Chuck the old one and insert the replacement, reinstall the screws and reconnect the electrical connector.

It's a one beer job.

Outstanding, sounds pretty simple. I will go ahead and order the part. Cheers

[amansopoor]

sounds to me to be the BMC as well. I had to change mine and if you remove the two nuts holding the relay back it will be easier to remove the BMCthe relay bank is right above the BMC

[RobOyo]

I need help too, I wrote before about my heater problem on my 1993 pontiac bonneville. the heater motor is working but the fan will not blow heat. the air that comes in with the dial on defrost seems to send a little warm air but the fan will not turn on, could this be a relay? where exactly are the relays? any ideas?????

[randman1]

RobOyo, when you say "dial" I assume that you have the manual climate control rather than electronic. You have a similar setup to that LMP describes above.

Fan speeds LO, MED1, and MED2 send voltage from fuse 17 I/P fuse box through a series of resistors to give you the different speeds. HI setting triggers a relay that sends voltage from fuse 3 RH underhood fuse block directly to the blower motor. Usually the two fuses do not blow at the same time unless the blower motor is shorted and you go through all of the fan speeds on the dial.

Check the fuses first and replace if necessary. Then begin checking the fan speeds. Set to defrost (or vent) and LO fan speed. Go through MED1 and MED2. the fan speed should incease. If it doesn't, you could have an open in the Blower Motor Resistor. But, it should still work on HI providing that fuse is good. If it doesn't work on HI either, you probably have a bad blower motor.