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Vacuum actuator and switch operation

Dave5701 on Mon March 14, 2011 10:00 AM User is offlineView users profile

Year: 79
Make: chevy

I thought I had this fixed, but nooooo. You guys helped me out a lot with this but the gremlins have returned. I had only air out the floor. I did some troubleshooting and found that the vac switch was hosed. I bought a new part, put it in and had air out the vents. Now, it quit again. I have a MityVac and put it on the main line to the switch, it wont hold vac. If i put some pliers on the main hose to the switch and pinch it off, it holds vac, shows that the main line to switch has no holes. The lines are very small, I ended up cutting one and the inside hole is like 1/16 or smaller, I don't have any splices that small. (any ideas on slicing? I have a larger splice and the hose will fit inside the splice, now what kind of glue will stick to the hose and plastic splice??) On the distribution side of the switch, it is like a molded clear plastic connector. The lines are permanently connected to it. If I take the MityVac and put it inside the connector, it directly pulls a vac to the actuators. Here is what I saw, I can pump up to about 10 inches and it slowly leaks down to about 2inches and holds. Is this normal?? Also, Is it possible that there are other problems in the switch?? The part I replaced is a circular part with little channels in it. It fits up against a flat piece with the feeder holes that drive each actuator as you move the selector slide switch from vent, heat, defrost. Could there be something wrong with this flat piece?? I do have a vac. schematic showing where all lines go, thanks to you guys, I can trouble shoot the thing, but need some good ole experience on how the actuators hold vac and if they look like they are working right, then onto the switch again.

GM Tech on Mon March 14, 2011 12:48 PM User is offline

All vacuum actuators should hold vacuum, if not, test each one individually, replace the leaky ones. The mighty vac is a good tool- I use one quite often for what you're doing.

No need to "glue" any vacuum splices. it is vacuum - right- that means the connection is always trying to cling together, not push apart, so no clamps, no glue needed, just make sure you have good snug fits-I'd avoid glue, just because you may clog up a connection. I often use rubber hose, and/or windshield washer hose for vacuum splices. You have to ask for windshield washer hose to get the parts man to understand what you want.

The number one A/C diagnostic tool there is- is to know how much refrigerant is in the system- this can only be done by recovering and weighing the refrigerant!!
Just a thought.... 65% of A/C failures in my 3200 car diagnostic database (GM vehicles) are due to loss of refrigerant due to a leak......

NickD on Tue March 15, 2011 6:13 AM User is offline

Hobby shops and now our True Value store sell that brass tubing in about 10" lengths that ranges from 1/16 to around 3/8 inches in outside diameter. Thank goodness, True Value sells it, use to have three hobby shops in town, and not one around in several hundred miles. Fleet Farm sells that vacuum line, recall it was around a dime a foot, replaced all of it in my old motorhome. Told the clerk to give me five bucks worth, how long is that sir? Figured that was another graduate of our unionized schools.

On some vehicles, that single reservoir stored checked valve hose, not only feeds the MVAC system, but the cruise control and parking brake release as well, so maybe not even with the MVAC system.

Accidentally got a little gas in my MityVac, that was the end of it, piston froze solid to the cylinder, got an all brass one with replaceable O-rings instead. Another tool I can not live without. But use to suck on those hoses and hold it close with my tongue, yuk, could pull 20"/Hg.

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