85 C10 Vacuum Hose Diagram/Pics

[hatred]

Have a 85 C10 and I can't get the AC to switch from the floor to vents. Blows really cold and strong, just won't switch. Had a couple of vacuum hoses under the hood unhooked and although I hooked them back up to a vacuum source, nothing had helped. I've scoured the web and forums and the stock diagrams only show partial, or parts I don't have. If anyone can take some pics for me under their hood I'd GREATLY appreciate it. Mine had the vacuum ball on the driver's side by the wiper motor.

85 C10, 305 auto with cruise (if that helps).

 

[75gmck25]

There is a vacuum reservoir (Black canister) under the hood on top of the A/C plenum. One vacuum line runs over from that reservoir to manifold vacuum. The other line on the reservoir runs over a short distance and then goes through a grommet in the firewall and over to your HVAC controls. That is the vacuum that runs to the vacuum motors.

Bruce

 

[hatred]

Mine has the plastic vacuum ball over by the wiper motor. I fixed and attached all the loose and open vacuum lines I could find. Foind a couple of small schematics and gonna try this weekend to iron it out. Is there anything in the ac control panel that would cause it? Everything i see inside it hooked up.

Tony

 

[75gmck25]

I don’t have cruise control, but I thought there was a reservoir on the driver’s side for cruise control and it was different than the one for the A/C.

The A/C controls have a vacuum switch on the back and a big rubber connector for all the vacuum lines. There is vacuum in, and a line to each vacuum motor. As you move the controls it slides the switch and sends vacuum to the right line. You may have a line disconnected or broken.

On the heater plenum up above your right foot (when driving) it should be fairly easy to see and reach the vacuum motor for Heat. If you pull off the line there you should be able to use it as a test point to see if you have vacuum.

If you remove the glove box door you can see the heat control Bowden cable and two of the vacuum lines. Up high above the plenum you can see the line coming through the firewall from the reservoir. You will also see a line coming across the top of the plenum, with a T in it to connect to the two motors for recirculate mode (one in the footwell and one up in the plenum under the hood).

If you take off the vertical plenum piece behind the glove box (one screw at the top and two at the bottom) you can see another vacuum motor on the back of the plenum. The last vacuum motor is inside the plenum, so all you will see/feel is a nipple sticking up.
With that plenum piece off you can see the heat blend door and the vacuum operated door. It’s also time to clean all the junk (mouse nests, etc.) out of the


Bruce

 

[hatred]

I don’t have cruise control, but I thought there was a reservoir on the driver’s side for cruise control and it was different than the one for the A/C.

The A/C controls have a vacuum switch on the back and a big rubber connector for all the vacuum lines. There is vacuum in, and a line to each vacuum motor. As you move the controls it slides the switch and sends vacuum to the right line. You may have a line disconnected or broken.

On the heater plenum up above your right foot (when driving) it should be fairly easy to see and reach the vacuum motor for Heat. If you pull off the line there you should be able to use it as a test point to see if you have vacuum.

If you remove the glove box door you can see the heat control Bowden cable and two of the vacuum lines. Up high above the plenum you can see the line coming through the firewall from the reservoir. You will also see a line coming across the top of the plenum, with a T in it to connect to the two motors for recirculate mode (one in the footwell and one up in the plenum under the hood).

If you take off the vertical plenum piece behind the glove box (one screw at the top and two at the bottom) you can see another vacuum motor on the back of the plenum. The last vacuum motor is inside the plenum, so all you will see/feel is a nipple sticking up.
With that plenum piece off you can see the heat blend door and the vacuum operated door. It’s also time to clean all the junk (mouse nests, etc.) out of the


Bruce

So I think I found out why my ac isn't switching from the floor to the ground all the way... 1st is the lever in the video supposed to move all the way over like it does with my hand? When I take my hand off it moves back. Almost like it doesn't have enough vacuum to hold it.

2nd can someone tell me where the other end of this tubing goes? Took the cowl vent off to clean under it and saw it broken. (Edit) I found the other end of the orange hose and connected it, but it still doesn't switch from floor to vent unless I push that lever all the way over)

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[chengny]

So I think I found out why my ac isn't switching from the floor to the ground all the way... 1st is the lever in the video supposed to move all the way over like it does with my hand? When I take my hand off it moves back. Almost like it doesn't have enough vacuum to hold it.

You don't mention whether the engine was running (or the position of the mode select lever) when you observed the connecting link moving back when released. That would be normal operation - if the engine wasn't running (i.e. not supplying vacuum to the control panel) or the mode control was set to one of the following: Off, Bi-Level or Heat.

There are four actuators used in a GM C60 HVAC system.

Three of the 4 are single acting (with vacuum applied to just one side of the actuator's diaphragm). The single acting style uses an internal spring to return to it's default position upon loss of vacuum supply.

One is dual-acting (vacuum can be applied to either side, depending on the position of the vacuum select valve). Without vacuum, this type will stay wherever it was left.

The four actuators and the components they control are:

1. Defrost/Floor damper actuator - single acting

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2. Outside air inlet damper actuator - single acting

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3. Cabin recirc inlet damper actuator - single acting

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4. Air distribution actuator - dual acting. This one actuator controls both the diverter valve (which directs air either up to the dash vents or down to the floor diffuser) and also the bi-level adjust valve . These two valves are mechanically connected by the "diverter valve link". That is the part shown in the first image you posted.

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The air distribution actuator, it's associated valves and the connecting link are all returned to the default position by a common spring. The spring is of the bi-directional type and will move all the components to a center position - no matter where everything was when vacuum was lost:

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[chengny]

Having said all that - sorry - check the diverter valve link. Access is easy, just remove the dash vent riser from the main body of the plenum (two little bolts and one screw):

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The connecting link will be visible. It is a white piece of plastic and gets brittle over time:

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This part is often found to be cracked and no longer attached to the diverter damper. Since the diverter damper shaft drives everything else, if the link isn't connected there is no control of air flow mode.

 

[hatred]

Having said all that - sorry - check the diverter valve link. Access is easy, just remove the dash vent riser from the main body of the plenum (two little bolts and one screw):

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The connecting link will be visible. It is a white piece of plastic and gets brittle over time:

You must be registered for see images attach

This part is often found to be cracked and no longer attached to the diverter damper. Since the diverter damper shaft drives everything else, if the link isn't connected there is no control of air flow mode.

I have the truck running when I'm messing with it. I fixed the hose to the actuator under the cowl, and the actuator for the fresh air by the kick panel works. If I push that lever over like in the video, the air starts coming from the vents, when i ket 8r go and it moves back, it goes back to coming out at the floor. I bought a handheld vacuum pump and a vacuum gauge to test all the lines and the hoses while the truck is running. I plan on tearing into the rest (under dash pieces you mentioned) tomorrow. Has to be a hose or bad actuator or that clip.

 

[hatred]

Having said all that - sorry - check the diverter valve link. Access is easy, just remove the dash vent riser from the main body of the plenum (two little bolts and one screw):

You must be registered for see images attach

The connecting link will be visible. It is a white piece of plastic and gets brittle over time:

You must be registered for see images attach

This part is often found to be cracked and no longer attached to the diverter damper. Since the diverter damper shaft drives everything else, if the link isn't connected there is no control of air flow mode.

Found this when I dug further into the dash... could this be why it's not switching from floor ro vent to defrost? Where would I get this part?

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[Rusty Nail]

Bingo

 

[chengny]

Found this when I dug further into the dash... could this be why it's not switching from floor ro vent to defrost? Where would I get this part?

In stock at Classic Parts - $4.49

https://www.classicparts.com/1971-87-Diverter-Valve-Link-Connector-W-A_C/productinfo/68-248/

 

[Rusty Nail]

Yeah . Part costs 4 bucks and they want 10 bucks to ship it?
AND you MUST register?
Suck it.


You give em your money.

 

[hatred]

In stock at Classic Parts - $4.49

https://www.classicparts.com/1971-87-Diverter-Valve-Link-Connector-W-A_C/productinfo/68-248/

I found two of them on Ebay real cheap. Wanted to buy the metal one but they wanted $40 for it shipped

 

[hatred]

Yeah . Part costs 4 bucks and they want 10 bucks to ship it?
AND you MUST register?
Suck it.


You give em your money.

Exactly why I went to Ebay. Bought two in case I need a spare down the road

 

[Rusty Nail]

Ohhh a mettel one?

Sounds badass!