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Bonneville Blower Control Diagnosis

Car: My daughter’s 1987 Pontiac Bonneville, 3.8 L V6, 65k miles onn odometer.

Problem: She reports that as she was driving home from work with the A/C on high and blower control set to High, the blower motor suddenly cut out.

I checked over the car, and the A/C compressor is still running fine. It turns out that the blower motor will run on Low, M1, and M2. But the blower motor will not run with the blower switch set to HI. Same deal with the heat. Lo, M1, amd M2 are fine, but blower motor cuts out when I move the blower switch to the HI position.

OK, fine. I pulled out my factory service manual for the car, and for these symptoms the manual says to do the blower relay and blower switch tests by testing voltages at various connection points.

My question is: In the diagnosis tables, under “correct voltage”, it frequently just says “Battery”. What does a correct voltage of “Battery” mean?

Any insights will be appreciated, and I will post back results. Thanks!

The correct voltage for “battery” is simply saying, whatever the current voltage across the battery is, you should see very close to the same thing at the point you are testing. No voltage difference.

The trouble with the blower circuit seems like it would have to be with the speed selection switch for the full on position. The high position bypasses the all the resistors and the relay is in the circuit for all speeds. You could prove that by using a jumper wire and bypass the switch connections for the high position. You could also measure the voltage across the switch connections. If you have more than .1 volts across the connection while the fan is set to the high position and it isn’t working then the switch is bad. The trouble may also be a bad connection to that switch position. Check the switch for a burned wire connection to it.

Hats off to you for owning a factory service manual for the car. You obviously know the value in having that on hand. Some of the best money you can invest in a car if you work on it yourself.

The problem might be with the high speed blower motor relay.

How this works is, on all the lower speeds, the relay switches the voltage to pass thru the resistor pack which provides all the lower blower speeds. When you turn on the highest speed of the blower motor, the relay switches the voltage over to apply full battery voltage to the blower motor.


Guys, thanks for the insights. Will post back what I find.

I found some data for the vehicle on the Autozone website. The drawing does not show any relay in the circuit which I was surprised at. Having that info, it looks to me that the trouble must be with the switch connection for the high speed setting. Bypassing the connection with a jumper will tell the story.

The autozone vehicle data I don’t think is as reliable or complete as it used to be. My factory manual definitely shows a relay in the circuit, and I have located the relay and appropriately colored wires (per the wiring diagram) on the firewall. I just have to get out there tomorrow night and do the tests. Autozone also has the relay in stock for 9.99, which is a good price if I have to replace the relay.

I went to the ARRC web site that my College subscribes to and also did not see a relay.

Mitchell On Demand and ALLDATA both show a blower motor relay.


This is interesting. Perhaps there is a model that doesn’t have a relay and one that does. Regardless, since the factory manual shows one there I would have to go with it. I still think you will find the trouble is with the switch.

Here’s a lesson I learned a long time ago. Unless the information on a wiring diagram also includes: Courtesy of Ford, GM, Toyota, Honda, etc…Motor Company, it can’t be believed.


I agree Tester. No one knows the car better than the manufacturer does. Factory manuals rule.

I performed relay test. I was supposed to get battery voltage on the red, orange, and dark blue wires. i did get battery voltage on the red and dark blue, but no voltage on the orange, which is the wire from the switch HI position. Next thing I need to do is test the orange for an open, which I will have to read up on how to do since I do not know how to test for an open. Another thing I noticed is one I removed the wire connector from the relay, that the connector had gotten hot in the recent past. There was a little melted plastic coverting all four of the wire contacts, which I had to scrape off in order to get my multimeter probes onto them. So this is where I am at with this job. Any further input is appreciated!

I guess at this point I am kind of stuck. I need to test this orange wire for an open, but the wire goes from the switch inside the instrument panel thru the firewall to the blower relay connector. How can I get one probe on the switch end, and the other probe onto the relay end? My multimeter probe wires are nowhere near long enough…

Any further input, guys? I’d be particularly interested in advice on how to check the orange wire (leading from the switch to the blower motor relay) as well as ideas as to why the connector shows evidence of having gotten too hot.

Since the blower works on the lower speeds this would mean that everything in the blower circuit is working. It is the high speed switch position that isn’t working so my guess is the switch contacts for that position are bad. You can prove that by simply placing a jumper wire across the switch contacts for the high position and see if the blower works then. If you want to use your ohmmeter place the probes of the meter across the contacts for the high position (with no power applied to the circuit) and see if there is zero resistance across the contacts.

I think most blower circuits control the speed of the motor by switching the return or ground side of the circuit through the resistors or in the case of the high speed position, directly to ground. If your system is designed that way then it would seem that the orange wire may have a bad connection at the motor end. Use your ohmmeter to check out wires end to end. A good wire will have zero resistance.

Since the orange wire goes from the switch to the relay (not blower), I guess I will have to connect a long wire to the switch contact and connect one ohmmeter probe to the wire, and then the other probe to the other end opf the orange wire at the relay connector. Seems kind of weird to introduce another wire into the process to test continuity on a circuit wire, but I don’t know any other way to do it, sice my ohmmeter probe wire is not 6 feet long. Will give it a shot. Thx.

A ten foot piece of wire with aligator clips on each end are pretty standard equipment for using an ohm meter. All an open means is that you have a break in the wire. If you have a break in the wire or an open, you will get no reading. I might be missing it but if you have a relay with melted contacts, don’t you think that is your problem? I suppose there is a chance the switch fried and drew too much current, but I think I’d sure look at the $10 melted part pretty hard first.

It wasn’t the relay that had gotten hot (I don’t think), but the wire connector to the relay that had gotten hot and partially melted at the very edge where it connects to the relay. I suppose the relay could be part of the problem, but the fact remains that the orange wire which is an input to the relay is supposed to carry battery voltage when the swtich is set to HI and it does not. So even if I replace the relay (which I probably will anyway while I am in there) there is still the problem of no juice on the orange wire, meaning HI will not work even with a new relay in there.

Thanks for the tip on the ten foot piece of wire with alligator clips. I will try that.

Having burned connections at the relay is a pretty common trouble. The problem could be due to either loose or dirty connections or bad relay contacts internally causing them to heat up due to the high current through the extra contact resistance. The heat then transfers through to the external connector and burns it. You may be wise to replace the relay just in case it is bad internally.

I do not have any info that shows the relay in the circuit. It shows that power is tied to the selector switch on a brown wire and the orange wire is tied from the switch to the motor and to the resistor pack.

I would assume that the blower relay is in the circuit for all the speeds and not just HI. Does your factory info show that or, is the relay only used for the HI speed selection?

Thank you, Yes I will go ahead and replace the relay. Here is the circuit diagram:

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