My parents have a 1998 Pontiac Bonneville SE with automatic climate control. The system has two issues. First of all, the blend doors will send air to the floor and the defrost vents, but not to the front vents. Pushing buttons on the control panel to change the vent selection produces relay clicks under the dash. Are the blend doors on this car actuated by vacuum, and if they are, is a vacuum issue plausible since it will change between defrost and floor vents (I think not, but could be wrong)? The second and more pressing issue is that the blower motor will only run part of the time. It either works as it should or doesn’t work at all, and the odds of it working on a given day seems to decline as the temperature drops. Are these two issues likely connected, and are they likely to be caused by the main control module (this device appears to control everything on this system)? I’m hoping not since that module is hideously expensive, and I know little about automatic climate control systems and am hoping somebody knows if and how it can be fixed without replacing the entire control module. Getting the blower motor to work when it is needed every time is the main priority, of course. Once again, I know little about these systems, my suspicions are mostly speculation, and I am hoping someone has seen this before and can help me avoid having to guess on a $500 part.
The next time the blower motor stops working, reach under the passenger side of the dash and with the handle of a screwdriver rap on the blower motor. If the blower motor starts working, replace the blower motor.
The ventailation mode problem will require a little more diagnosis. It could be a problem with the vent control module or a problem with the mode doors/motors.
That was the first thing I tried when I saw this the first time. The blower motor is actually mounted to the firewall on this car. Hitting it with a screwdriver had no effect, but unplugging and replugging the harness made it work again. I think this was a fluke, though, because the next time it happened, my father tried the same thing and it didn’t work.
Then you might be looking at a defective vent control module. The blower motor is controlled thru that also.
If you have a test light or a volt meter (should have one anyway), when the blower stops, check for voltage at the plug. If you have it, then the motor is shot. GM blower motors are notorious for making noise and intermittant operation. My only thought on the module, if we are talking about the blower module, is that if it fails I thought the blower would run continuously even when the car is off.
As far as the vent door, I would suspect a vacume problem. You’ll have to do some disassembly under the dash to get at it and if it has hoses going to the vent motor, check to make sure vacume is present. Check the condition of the vacume line under the hood going to the firewall. I had one actually burn a hole in the hose and caused a similar issue with the vent. To confirm, you can run a long hose from a vacume source in the engine to the vent motor to see if the condition changes or not. Then you know you have a line problem or a vacume motor problem. The other thing is that I believe it will have an HVAC control module that controls everything. It will be a box with a number of colored vacume lines going to it. If this is bad, it can also cause similar issues. Both the blower module and HVAC control can be had at a junk yard for not too much money.
You kind of need the factory service manual for trouble shooting detail on the HVAC systems though.
I can answer the vent issue. It’s a common issue, I have a 98 LeSabre which has the same control box. The vacuum is connected via a male female conector at the programer (name for the box behind the glove box). The rubber in the male conector gets soft over the years and collapse when vacuum is applied. The way to fix it for 1.60 and about 30 min of time. First you need to remive the programer and then open it up. Cut out the male plug and bring it the autoparts store. You need to buy some small vac line that will fit over the vac line that used to hook into the back of the male plug. Back at the car attach a length of vac line to the loose vac lines that were running to the back of the male plug. Push the other ends into the Oppropriate female plugs.
Sorry i am typing on my ipod and its small. Plug the controller back in and it should all work. Ps I did not say it in the first post, but make notes of which vac lines connect to which vac lines before you cut out the male plug.