HVAC vacuum inches

['87 Turbo "T"]

Hey guys. Troubleshooting my A/C not coming through the vents. I'm aware it could be an actuator as well as a stuck door.

I have about 13" of vacuum on the line at the fender vacuum ball & 13" where the violet hose connects to the vacuum control switch. However when I switch to NORM, BI-LEVEL, OR VENT I drop to about 7"-8" of vacuum on the blue hose.

My question is this: Is this enough vacuum to actuate the actuators? Figured I should have more if I have 13" coming into the switch. I do hear a small vacuum hiss from the 9 port switch. Could I be losing 5"-6" there?

Is there anyway to fix these vacuum switches? They are like hens teeth to find.

Thanks!

 

[salvageV6]

Where does the A/C fan air come through now? Floor or defroster vents, both, all of them including dash vents?
I would put a good vacuum source either from the purple line to the blue line with a plastic coupler or from the engine bay to the blue hose with a coupler or use a mityvac as a source and see if the bellows moves to the proper position to get air out of the dash vents to isolate the problem more.

 

['87 Turbo "T"]

Well for a while I’d leave it on NORM or VENT. It would come out of defrost & floor then after a bit it would transition over to the vents. I’m trying that to get the system doors moving.

Now it’s just defrost & floor. So I’m troubleshooting to see if it’s a vacuum issue or an actuator, or door issue. I hear a slight hissing from the vacuum selector. Looked in the FSM cause I was wondering how much vacuum is needed for the actuators.

I like your idea. Lent out my MityVac. So I may just take the purple to the blue or even the purple all the way to the actuator. A dealership by me can get the vacuum switch but OUCH on the price for two plastic pieces & a piece of rubber.

 

['87 Turbo "T"]

Got it all squared away. Applied vacuum directly to actuator & it switched to vent. Messed wit the vacuum selector & got 13” on the blue line to actuator.

Hooked it up, ran through all the settings, & all is good now.

 

[1986 Buick GX1]

Got it all squared away. Applied vacuum directly to actuator & it switched to vent. Messed wit the vacuum selector & got 13” on the blue line to actuator.

Hooked it up, ran through all the settings, & all is good now.

That’s awesome!
What was the fix? Is there a way to tighten the selector switch? Silicone grease?
Thank you

 

['87 Turbo "T"]

To be honest, I'm not 100% sure. I seem to have possible had a leak in the tubes going from the actuator to the connector. I replaced those & vacuum got better. I took the actuator apart, cleaned the rubber piece, pried the metal star piece on the connector to make it fit a bit tighter, cleaned out the vacuum holes & matched the valve to the correct setting.

I DID NOT use silicone grease. Kind of wishing I would have but that would've meant taking everything back apart. Voila! Switched to VENT & a few seconds later the door slammed shut & air out of the vents. The vacuum actuator is $80+ bit too pricy for two pieces of plastic & a rubber disk.

 

[Turbo6inKY]

To be honest, I'm not 100% sure. I seem to have possible had a leak in the tubes going from the actuator to the connector.

You had a leak, you diagnosed it in the first post.

When you moved the actuators and the vacuum changed from 13" to 7", that was the leak. If it was sealed, you would have seen a disturbance in the gauge moving the actuator as the air was removed from that section of the circuit, but it would have stabilized back at 13" almost immediately. The fact it didn't means it was pulling air in somewhere.

Taking it apart, replacing the crusty old connectors and cleaning it was the right move. I wouldn't worry about missing the silicone grease. As long as the connectors are still supple and the ends of the lines are clean and the lines aren't cracked, they'll seal fine.

 

[jmidolo]

Where is the actuator you were testing? Got the same problem. The one behind the glove box works fine but getting the same defrost and floor only like you had.

 

['87 Turbo "T"]

It’s behind the instrument panel/dash. To the left of the heater controls. It’ll be closer to the firewall. Has a blue vacuum hose running to it.

Take out your HVAC control, look to the left & you can see it. Not the easiest to get to but I can be done. Vacuum hose is clipped to the heater box assembly.

 

[jmidolo]

Thanks. So you don’t need to pull the speedo it’s accessible thru the radio hole?

 

['87 Turbo "T"]

Nope. Should be just fine pulling the heater control unit. It’s not super easy to get to but doable.

 

[6gunn]

To be honest, I'm not 100% sure. I seem to have possible had a leak in the tubes going from the actuator to the connector. I replaced those & vacuum got better. I took the actuator apart, cleaned the rubber piece, pried the metal star piece on the connector to make it fit a bit tighter, cleaned out the vacuum holes & matched the valve to the correct setting.

I DID NOT use silicone grease. Kind of wishing I would have but that would've meant taking everything back apart. Voila! Switched to VENT & a few seconds later the door slammed shut & air out of the vents. The vacuum actuator is $80+ bit too pricy for two pieces of plastic & a rubber disk.

Bringing this thread back for a bit as I'm going through the same problem. I've found that the two little tabs that hold the vacuum actuator switch together are broken causing no seal. Short of buying a new one from Highway Stars, is there a fix for this that gets rid of the plastic through piece with that star washer? How about using a thin nylon nut/bolt loosely tightened? Any ideas?