77 Buick Climate Control Problems

[GlennDegere]

I am having problems with the climate control system in my 77 Buick. At first the system works without any problems. After driving for about 20 minutes the blower motor quits except for in defrost. I have tried replacing the blower relay which was not the problem. After reading the service manual it says something about an "in car switch" connected to the control panel. I removed the control panel from the dash and could not locate this. Where could this be? Also it mentions a "thermostatic switch" and a "cylinder head metal temperature heater switch" Where are all of these switches located and could any of them be the culprit to the problem?

Thanks,

Glenn Degere

[Don B.]

In the controls is a vacumm switch if the hoses come off

the system will act erractically. I'd also check engine

vacumm hoses for spongy or hard hoses and replace them.

[NTX5467]

If you haven't checked earlier, make sure the vacuum supply lines to the basic vacuum reservoir under the hood (which could use a manifold vacuum port or a tap from the vacuum line at the power brake booster) and then to the control head in the instrument panel and then to the programmer under the passenger side of the instrument panel are all in good shape. There might be some electronic sensors, but modulating and directing vacuum to particular parts of the programmer servos is what makes things work with regard to changing the air flow to different functions. With a "normal" systen, when the air goes to the defroster and floor vents, that's the default mode for a loss of vacuum to the control head--might be similar with the automatic systems too.

If the vacuum tap is at the power brake booster, it could also supply vacuum to the cruise control system too.

It might be a good idea to find a GM Parts book (earlier edition) that might have a more detailed picture of the system you have than the more current versions in the computerized parts database systems we now have. This can be more informative, as to where things are located, than the GM service manual for the car might be.

Just some thoughts,

NTX5467

[Guest Dans 77 Limited]

When I first bought my Buick , the heater control panel was bad ,and I was told this was a common problem for 77 GMs. So I went to the boneyard and yanked a control panel out of an 83 LeSabre, there are some minor appearence differences but you would really have to know what you were looking for to know its not the original panel.I dont know if this would be the cause of your problems because my 77 does not have climate control, but it might be something to keep in mind. Hope this helps.

Dan

[Coolabah]

I am having a similar problem with my 77 Riv. The blower would operate intermittently, then only on defrost, now not at all. I believe the problem is a failed electrical switch in the A/C Programmer, which is located above the right-front passenger's feet. Strange buzzing noises (arcing across the switch contacts?) were emanating from that area. The Automatic A/C Programmer has electrical and vacuum inputs and outputs, and outputs movement of an air-door actuator.

My 1978 Chassis Service Manual (believed to be equivalent/same as 1977) discusses the system operation in Section 1C. See Figure 1C-4 and 1C-38. The presumed-to-be-malfunctioning switch is identified by the "Five Pin Connector" in Figure 1C-4.

Local Buick dealer shows entire assembly to be "discontinued", so no chance at a switch only. Parts diagram shows it as item 20, group 9.275.

Would appreciate info on availability of replacement switch.

[NTX5467]

A few thoughts that may or may not apply . . .

A solid vacuum source is still required on these systems for the vents to change, just as on the manual a/c systems. Default mode is air through the defroster and floor vents at the same time and not changing from that situation. On the '80s cars, the vacuum source was a check valve in the cruise control system, with a tee on the vac source side. Very bad about cracking and making the a/c vac go away. Sometimes, over near the power brake booster.

On the '90s automatic a/c systems, there was a circuit board that was located under the hood, in the a/c case. Had a pretty good size electrical connector, and when you pulled it out of the case, an aluminum heat sink with some transistors on it. If the blower motor per se had any problems (other than failure), it was most likely this "blower motor control module" having "problems". I suspect there would still be some sort of "blower motor resistor" in the a/c case under the hood on the earlier systems, so that could be an issue with the blower motor issue.

Although there would be "no user-serviceable parts" in the programmer assembly, it might be that it could still be openned up and cleaned appropriately by somebody that had some time and appropriate tools to use, plus being aware of how fragile some of the parts in that assembly might be at this point in time (LOTS of plastic!).

IF you heard a humming noise, it could also be one of the vacuum switches/modulators in a particular "resonance" mode at particular vacuum levels. On one of my cars, I replaced the factory water valve with an aftermarket one, with a smaller vac "can" on it. At certain vacuum levels, the switch in the dash would loudly vibrate, but a factory valve with the larger vac can never had that problem. There were some Buick water valves that were run by a flat stepper motor that bolted onto the water valve--pretty trick stuff!

Many times, when some electrical switch fails, it might be due to the component it controls having problems and drawing too much "juice" through that circuit. When that happens, things upstream in the circuit from the failing component "cook" at the location of least resistance. And do this without blowing any fuses. So . . . one thing could well lead to another.

It's been a while since I looked at those earlier systems in the parts database, but I suspect they were an evolution of the earlier Comfotron systems of the '60s and '70s. Could be some common parts with similar Cadillacs and Oldsmobiles, but the programmer might look different from the other carlines. I suspect there will be a basic potentiometer/rheostat to control the temperature functions, which in concert with other sensors/aspirators will determine what vents open when/where/blend and how much. Not to mention appropriate fan speeds too, depending on the actual and desired temperatures.

Might take several hours, some jumper leads, some vacuum source (hand-held pump, for example), the factory manual, and patience. One of those jobs that should be scheduled without any outside interruptions.

Just some thoughts,

NTX5467