VCCA Home Forums TECHNICAL - 1945 AND NEWER 1980-1989 Interior Fan Cuts Out

Here's a puzzler (to me anyway): I was driving my '87 Caprice today with the AC on and the blower fan set to the first setting above "off" I then approached a hill (incline). As I leaned more on the accelerator to maintain my current speed (about 60 mph) the blower fan stopped; no air movement and of course it got warmer inside the car. When I noticed this, I held my hand in front of the vent; sure enough no air movement at all. As I r crested the top of the hill and pulled back a bit off of the accelerator, the fan gradually came back on. This happened once more on another incline. No further abnormalities after that, even when returning to surface street traffic.

Has anyone experienced this before? Any ideas what could cause this?

Thanks in advance for any insights!

When climbing the hill the engine vacuum supply was reduced. The heater controls are activated by vacuum. There is either a vacuum line,vacuum motor. or Vac. control leaking.

Ah-hah! Thanks Chev Nut!

Matt

That is a typical problem with GM vehicles of that period. It happens to me fairly often. The same problem has also appeared on GM vehicles that friends of mine own as well.

On my car, when the problem occurs due to lost vacuum, the diverter door closes and the air is then directed from the upper outlets on the instrument panel to the heater outlet on the floor. Once the vacuum is regained the diverter door changes position and then the air is redirected back up to the upper air conditioning outlets once again. Your blower fan is not actually shutting off....the air is being redirected to the floor outlet.

There is a small plastic vacuum control valve behind the instrument panel that has several vacuum hoses going to it. Because the valve is plastic it tends to leak after a period of time with use therefore vacuum is lost going up hills or when you do a fast acceleration. I have replaced my vacuum control valve several times in the past and each time the new valve has cured the problem until it starts leaking again. I always carry a new spare vacuum control valve in the glove compartment.

Wow, thanks Junkyard Dog! Would you happen to know the part number from the last time you purchased one? I found this, no picture, for $20.

Chevrolet Genuine Factory Part
Part Number: 14039627..?

I have a 1984 Oldsmobile and the part number for the vacuum control valve on that car is 16037778. The vacuum control valve is a Delco.

There is also a one way check valve on the engine side in the vacuum line. Most vacuumn control systems will default to defrost with no vacuumn, defrost is more important than heat on the floor.

I had the wagon out again Friday, AC on and came upon a steep hill again. You were right! While climbing the hill the cold air was diverted to both the floor and the windshield outlets. Thanks again guys for helping me figure this out!