ac vacuum lines

[kc87]

Hey guys I need a little help here. I'm trying to figure out where all the vacuum lines go that run the AC duct dampers. I've found very little info on this and my manual leaves a lot to be desired. Does anyone have a diagram for these lines or know where I can find one? Thanks

 

[kc87]

OK I figured it out. It took taking the entire unit out of thej truck to diagnos how everything works, or in my case didn't work. But it was all full of leaves and dirt so it needed to be cleaned out anyways. Being I found no documented info on how this stuff hooks up I figured I'd let y'all know what I figured out. First off my system is in an 87 k10 and there are 5 lines. Lines are black with colored stripes. Colors are grey, orange, blue, brown and solid black. First off the grey one is the main vacuum supply for the system witch goes through the firewall. I never found where it actually hooked up so I'm just going to tap into a line that has full manifold vacuum to supply the system. The orange line supplies two actuators there is a tee in it behind the glove box on line goes to the actuator located in passenger side kick panel. This is for the door that allows air from inside the cab to recirculate on Max cool setting. The other orange one off the tee goes through a rubber gromet on top of passenger firewall and connects to actuator located under cowl between Hood and windshield. This lets in outside air.

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[kc87]

Having issues uploading pics. Guess I'll have to do one at a time. Connection under cowl.

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[kc87]

Next are the brown and blue lines. These run to an actuator located on the back side of the unit and I don't think you can even get to it while its installed in the truck. This actuator operates the damper that switches from vents to floor/defrost. The blue connects to the nipple on the side of the actuator and the brown connects to the nipple in the center of the actuator.

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[bucket]

Nice! Did you get yours working how it should? I'm sure this info is going to end up helping a lot of people.

 

[kc87]

Last one is the solid black. It connects to the actuator located on the left side of the unit. Just left of the floor air outlet. This damper switches air from floor to defrost.

 

[kc87]

Switch position dictates vacuum on these lines. Off -blue,max-brown&orange, norm-brown, bi level-none, vent-brown, heat (floor)-blue, defrost-blue&black. I hope this helps someone out along the way.

 

[kc87]

Nice! Did you get yours working how it should? I'm sure this info is going to end up helping a lot of people.

Thanks man! It was a pain in the a$$ but yeah it seems to be working the way it should. All ready for the next problem to arise.

 

[bucket]

Switch position dictates vacuum on these lines. Off -blue,max-brown&orange, norm-brown, bi level-none, vent-brown, heat (floor)-blue, defrost-blue&black. I hope this helps someone out along the way.

So if I can hear a slight vacuum leak at the control head, that would explain why my heat and AC always come out the floor AND dash vents, right?

 

[kc87]

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.

 

[kc87]

So if I can hear a slight vacuum leak at the control head, that would explain why my heat and AC always come out the floor AND dash vents, right?

When selector switch is in a/c position you should have vacuum on the brown line. That is where I would start checking for leaks. However if there is no change in airflow no matter what position selector is in
Defrost, a/c, heat etc. You may have a leak in the main vacuum line (grey one).

 

[bucket]

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.

Yeah, I know about the disc, I've replaced a bunch of them in older Cavaliers, Camaros, Astros, S-10's, etc. Except in those vehicles, a vacuum leak at the switch would cause air to come out the defogger vents only. That's why my Burb has had me confused this whole time. When I first got it, I tore the dash all apart, sealed up leaks and all that, and everything was working fine. Then after I put the dash pad and cluster bezel back on, my floor/vent problem was back. I said screw it and that was about 7 years ago.

When selector switch is in a/c position you should have vacuum on the brown line. That is where I would start checking for leaks. However if there is no change in airflow no matter what position selector is in
Defrost, a/c, heat etc. You may have a leak in the main vacuum line (grey one).

My airflow does change to defog. But heat position blows some out the vents too, and AC position blows some out the floor.

 

[82chevy350]

You should make a diagram in paint

 

[89Suburban]

You should make a diagram in paint

Wow good job digging this thread up, I never saw it before and has great info. I'll get the diagram posted here shortly.

 

[Tim K]

The '87 factory manual does have a diagram and the color codes for the vacuum hoses.

How does one get the control unit out of the dash without tearing apart the whole dash? I need to check the vacuum hoses sealing as currently there is no control over the outlets. After removing the 4 screws holding it in place there does not seem to be enough slack in the hoses to pull the unit free of the dash.

In trying to diagnose the problem I pulled the vacuum supply in the engine compartment and installed a mighty vac on the hose, pulled a vacuum and then had my girl switch the controls between the different vent positions. Some held the vac and some dropped to zero so I assume those hoses are probably shot and need replacing. Any ideas?