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vaccum actuator

Guest roy341

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Guest roy341

1967 cutlass with factory air

there is a vacuum actuator, i think for the blend or recirc control.

a. if this is not working how badly does it effect the performance of ac?

b. how do you test to assertain whether it is working or not?

c. has anyone replaced this item on a similar car? how is it replaced?


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On the back of the a/c control in the instrument panel, there's the master vacuum switch which runs all of the actuators in the hvac system. Many were pot metal and "wore" with age and use. Just two cast pieces of pot metal, machined to fit against each other without any anti-friction interface between them. It could well be that THAT's where the vacuum leak might be, so that'd be the first thing to check. Next inline would be the actuator itself. Just a simple vacuum diaphram item. Perhaps the rubber inside has deteriorated or something, resulting in a vacuum leak at that point when the particular actuator is activated.

The main vacuum source is the intake manifold. From there, the vacuum supply line probably goes to a vacuum reservoir near the a/c system in the underhood area. This is where the vacuum is before it goes inside the car to the vacuum switch on the a/c control.

"Blend" and "Inside Air" are two different issues. "Blend" would be temperature-related, adding some heat into the cooler air after it passes through the evaporator coil. "Inside Air" (as I call it) is where the air inside of the passenger compartment is recirculated, as oppposed to "Outside Air" where very little inside air is recirculated. "Inside Air" usually blows harder for the same fan speed than "Outside Air" does, unless you're running into a headwind at 80mph road speed. If it's really hot and/or humid, a/c performance on "Outside Air" would be a little less than if it was recirculating the cooler (and getting cooler still) "Inside Air".

First, though, you need to determine where the vacuum leak might be . . . the vacuum switch on the a/c control, a cracked vacuum supply line from the engine, or an aged a/c actuator under the instrument panel. On many GM a/c systems, when the vacuum supply to the system goes away, the default mode for the vents is "floor vents and defroster vents", even if you select the a/c mode. The rest of the system will operate normallly, but the air output will only be "floor and defrost" as if you've gotten a "heat" function selected.

IF the vacuum selector switch is where the leak is, it might be possible to unclip it and take the two halves apart for inspection. Then, possibly take some rougher (then finer) sandpaper to re-finish or "dress down" the two mating surfaces. IF you can make this happen successfully, then you've saved a good deal of money that you didn't have to pay one of the restoration a/c parts vendors.



Just some thoughts . . . please keep us posted.

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