ac vacuum lines

[flyboy1100]

Everything works at idle, just not while driving. The accumulator is only hooked up to my cruise, so that should be my problem. Need to go get some tees unless the cruise shouldn't be hooked up on that same line. Thanks

 

[chengny]

If it just stopped working correctly all at once - 2 days ago - I would carefully check the vacuum hoses for newly developed leaks.

The selector side of the control system is actuated by vacuum - that vacuum is obtained from the intake manifold. When the throttle plates are fully closed (like when at idle), the vacuum under them (and within the intake manifold) is at it's greatest.

If there is a small leak in the tubing, the deep vacuum created at idle can keep even a leaky selector system functional. This is because it either provides enough make-up vacuum to overcome the amount lost through the leak - or it is strong enough to temporarily pull the leak in the hose closed.

When you accelerate - and the throttle plates open - the vacuum within the intake manifold falls off.

If there is a leak anywhere in the tubing, the deep vacuum that you had at idle is no longer available to replace the lost vacuum signal (or pull the leak in the hose closed). Pressure rises in the tubing and control of the selector system is quickly lost.

Letting off the gas closes the throttle plates, manifold pressure drops and the strong vacuum supply is re-established to the HVAC control system.

Bear in mind that even with a properly functioning selector control system, there is no real "flow" within the tubing and actuators. Only when a different setting is selected does the control valve vent to atmosphere.This venting is only in the hose to the actuator that is being moved and the vent port does not connect to the rest of the system.

So basically, if you have a tight system and it is connected to the reservoir, you should maintain control for a good long time - even without manifold vacuum applied.

 

[flyboy1100]

Poor wording on my part, i noticed it wasnt working correctly. It probably hadn't been since i got truck, the conditions were perfect for needing defrost, but it was mixed everywhere until back at idle. It has been like and i thought maybe that was how it should be. I never tried changing settings and noticed the lack of a change until yesterday. Just haven't been paying attention....


I know for a fact it is hooked up to the manifold vacuum port on intake and not to the resevoir as it should be. I plan to fix that tonight or at least by Saturday

 

[chengny]

Pull the check valve out of the tubing and check it for proper function. You can use your mouth.

Blow in the direction indicated by the arrow - you should get good flow.

Blow the other way - you should get no flow.

 

[flyboy1100]

all the underhood stuff is taken care of. when i get a chance i will try to get the switch portion cleaned up. can i buy a replacement disc thing? there is still some leakage (20-30% best guess) everywhere, but nothing like when the vacuum was dropping off.

 

[chengny]

Classic Parts has the complete selector switch for $17.95:

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(1985-91) Heater & A/C Vacuum Selector Switch

Fits trucks with air conditioning. 85-87 pickup trucks 88-91 Blazer, Suburban, & Crew Cab R/V series

http://www.classicparts.com/1985-91...ector-Switch/productinfo/68-338/#.VMKyFNKNfmU

 

[flyboy1100]

Sweet!

 

[sealacamp]

Yeah sounds logical to me. I pulled the vacuum switch out of my control unit and disassembled it to try and make sense of the whole vacuum mess. There is a rubber disk with a maze of groves cut in it that sits against the plastic manifold that your vacuum lines all connect to. On mine the rubber disk was dry and dirty so cleaned it and put a little dielectric grease on the two surfaces. One to keep it from drying out and cracking and two to help the two pieces slide together. It was leaking before I did this and it appears to be sealing good now. If you do take it apart pay attention to the position of rubber disk and be sure it goes back the exact same wayit came out. It is easy to put it back 180° in the wrong direction. I could just be the vacuum line plug is just not sealing good.

Ok my truck is still together, 81 C10, I know how to get the issue resolved with my controller but I'm not sure how to get the switch in my hand so I can get it connected again. Some nut before me has monkeyed with it and I can see what the issue is just can't get my hand on it. How can I get the switch out with out taking the entire dash apart? If there is a way to do it can someone please clue me in?

Thanks

 

[chengny]

It's not necessary to pull the dashboard or the instrument panel, however you will need to remove the dash bezel. But don't stress, it's not hard at all:

1. Release 4 screws and remove the lower trim piece from the steering column:

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2. With the lower trim removed, two more screws will be seen behind it (circled in red). Remove them along with the eight remaining bezel mounting screws (circled in yellow):

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3. If you still have a stock radio,the knobs might have to be removed. The headlight switch knob/shaft can stay in place - the knob will pass through the hole in the bezel.

4.The upper center A/C duct will stay attached to the bezel and come away with it.

5. With the bezel removed, you will see the 4 screws that secure the control panel to the dash:

You must be registered for see images attach

Release them and the control panel will be able to pulled into the cab - a little bit. The cable to the blend door will limit how far the panel can move.

But there should be sufficient slack to allow you to release the vacuum harness connector from the selector switch.

If you need help removing the selector switch body from the controlpanel frame come back.

One tip:

If it is necessary to pull the silver tips off of the selector/temp control levers - do that step while the panel is still screwed to the dash. They are sometimes very difficult to pull off the lever rods. I usually wrap them with a piece of leather or cloth and grasp them tightly with a pair of Channellocks. Then, while rocking the tip back and forth, I pull on it HARD and they usually pop off. Replacement is easy - just jam them back on to the lever ends.

 

[sealacamp]

It's not necessary to pull the dashboard or the instrument panel, however you will need to remove the dash bezel. But don't stress, it's not hard at all:

1. Release 4 screws and remove the lower trim piece from the steering column:

You must be registered for see images attach

2. With the lower trim removed, two more screws will be seen behind it (circled in red). Remove them along with the eight remaining bezel mounting screws (circled in yellow):

You must be registered for see images attach

3. If you still have a stock radio,the knobs might have to be removed. The headlight switch knob/shaft can stay in place - the knob will pass through the hole in the bezel.

4.The upper center A/C duct will stay attached to the bezel and come away with it.

5. With the bezel removed, you will see the 4 screws that secure the control panel to the dash:

You must be registered for see images attach

Release them and the control panel will be able to pulled into the cab - a little bit. The cable to the blend door will limit how far the panel can move.

But there should be sufficient slack to allow you to release the vacuum harness connector from the selector switch.

If you need help removing the selector switch body from the controlpanel frame come back.

One tip:

If it is necessary to pull the silver tips off of the selector/temp control levers - do that step while the panel is still screwed to the dash. They are sometimes very difficult to pull off the lever rods. I usually wrap them with a piece of leather or cloth and grasp them tightly with a pair of Channellocks. Then, while rocking the tip back and forth, I pull on it HARD and they usually pop off. Replacement is easy - just jam them back on to the lever ends.

Wow that was quick and well worth the price of admission. <(^_^)> Thanks a ton. I'll try to get around to tackling that in the next few weeks. Got to get the wheel cylinders replaced in the rear this week, did the front flexible brake hoses last week. Slowly but surely it's coming back together. My truck originally had AC but someone removed most of the parts and it appears removed some of the capillary vacuum lines as well. I can see the issue but can't touch it. Your guidance should get me through this mess chengy, thanks a ton.

Sealacamp

 

[chengny]

No problem, glad to help.

One thing to bear in mind however; any experience I do have with these 81-87 series trucks is limited to the later model years (85-87).

So the advice I offer (and the images I post) are sometimes not applicable to the earlier model years.

 

[Alexandr-Rychok]

was wondering if anyone could tell me what vacuum lines are necessary for the motor to run, have a bobber project i am attempting and the vacuum lines are the last thing that i need in order to have the bike finished.

 

[chengny]

was wondering if anyone could tell me what vacuum lines are necessary for the motor to run, have a bobber project i am attempting and the vacuum lines are the last thing that i need in order to have the bike finished.

You must be registered for see images attach

Most motorcycles - esp those designed for use in the Ukraine - don't come with an air conditioning system.

 

[flyboy1100]

You must be registered for see images attach

Most motorcycles - esp those designed for use in the Ukraine - don't come with an air conditioning system.

They do have a/c but it is indirectly controlled by air temp and speed.

 

[Motor City GMC]

Thia is all very helpfull but im just hoping it applies to me!! Lol
I have a 79 K30 with a/c is this the same for my year as well?