HVAC Vacuum Controls

Hi, I've got an 82 K25 with AC. Anyone know where this vacuum hose goes when it goes off into the firewall. The one that comes in from the engine is to the left of it and lower. I'm thinking it goes to the AC somehow? Anyway, the kick panel vent flap never opens on my truck and I don't believe it ever has. Any ideas on when it should open or what to look for? All my other flaps work, although slowly. If there is a way to clean and oil them, I'd rather do it now while the dash is apart.

my kick panel flap only opens when the slider is on max.

the 85 k20 that is.

callmewaylon said:

Hi, I've got an 82 K25 with AC. Anyone know where this vacuum hose goes when it goes off into the firewall. The one that comes in from the engine is to the left of it and lower. I'm thinking it goes to the AC somehow? Anyway, the kick panel vent flap never opens on my truck and I don't believe it ever has. Any ideas on when it should open or what to look for? All my other flaps work, although slowly. If there is a way to clean and oil them, I'd rather do it now while the dash is apart.

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It goes to another vacuum motor that's part of the recirc system. im not familiar with the 81 up cowl but suspect you have to remove the panel to access the motor.

On my '75, with the hood open I can remove the screen that is right under the cowl area and I can see that 2nd vacuum motor that is connected to that line. However, I thnk they changed the hood intake arrangement a little in later years.

Is your vacuum line into the engine area connected to a vacuum reservoir, or directly to engine vacuum? There should be a vacuum line from the engine over to the reservoir (shaped like a ball) near the A/C housing, and then the line from inside the truck connects to the other port on the vacuum reservoir If you are running directly off engine vacuum you are probably not getting very good vacuum to the A/C system most of the time.

The vacuum motors are also slow to respond. As I change dash slider positions it sometimes takes 2-3 seconds for the motors to respond, and the recirculate air motor may take more like 15-20 seconds. I don't think lubrication will help much.

Bruce

Yes, my vacuum resevoir is hooked to manifold vacuum and then the small line hooks to it and runs into the cab. Tomorrow I'm going to pull the line off the kick panel and make sure it's getting vacuum when the AC is on max. Also, the control switch that all the vacuum lines plug into may not be in great shape. Moving the lever it is kind of sloppy and the detents aren't really distinct anymore. Looks like the 82 and earlier vacuum controller is hard to buy. I only found 1 place selling reconditioned ones and another one selling new reproductions that weren't available yet. The originals are unavailable everywhere.

Okay, so I got the cowl off and found the vacuum door under the cowl. Next issue is that I'm going to need new pins for the back of the metal cowl grill. Anyone know where to get them?

Very timely post. I just opened up my glove box a few minutes ago, and found that exact vacuum hose, with grommet attached, wrapped around the wires going to the glove box light, and kinda hanging into the top of the glove box. What the heck? So apparently my vacuum line has been cut, inside that fresh area intake cowl? Wonder how long that's been like that.

Couple questions:
1) does this vac hose that has a grommet on it, and pushes through the interior firewall skin from just above the glove box "box" area, connect to a vacuum reservoir that's located inside the fresh air cowling below the windshield? The diagram above shows a vac reservoir, but isn't very clear on location.

2) does the vac hose from the engine, which enters the engine side of the firewall just below where the engine area "work light" is located, attache to the vac reservoir?

3) Can someone post a photo of the inside cowl area, showing the vac res (if that's where it's located)? I didn't bring tools home from work, otherwise I'd be out there removing the cowl that's in front of the windshield

1. That vacuum line connects to a vacuum motor mounted in the cowl area. Up behind the glove box there is a T in that vacuum line, so it also connects to the vacuum motor in the kick panel on the passenger side. In recirculate mode it closes the flap in the cowl (shutting off most of the fresh air) and opens the flap in the kick panel (to let A/C draw air from inside the truck).

2. Vacuum hose from the engine runs over to the vacuum reservoir under the hood and connects to a port on the bottom. My reservoir is a short black canister mounted on the firewall just above the blower motor housing. There is a 2nd port on the bottom of the canister, which is where the vacuum line from the HVAC connects after it comes through the firewall.

3. I don’t have a picture of that area. On my truck the vacuum motor is very hard to see unless you can almost directly above the cowl and look into the corner on the passenger side.

Bruce

Hopefully this will help. The vacuum pod under the passenger side cowl is attached to a plastic flap that controls fresh air. If you remove this, be careful. It will rip easily due to age. This pod and the one on the passenger kick panel are connected and only operate in MAX mode. The flap under the cowl closes off the fresh air and the kick panel door opens to allow recirculating air.

Craig 85 said:

Hopefully this will help. The vacuum pod under the passenger side cowl is attached to a plastic flap that controls fresh air. If you remove this, be careful. It will rip easily due to age. This pod and the one on the passenger kick panel are connected and only operate in MAX mode. The flap under the cowl closes off the fresh air and the kick panel door opens to allow recirculating air.

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Good info and very true.
I was checking the vacuum pod for functionality under the cowl of my k5 while it's apart for paint.
The flap turned to dust when I touched it. I was able to find a good used one at a yard.

Not sure where to find a new one.

RoryH19 said:

The flap turned to dust when I touched it. I was able to find a good used one at a yard. Not sure where to find a new one.

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I found one on ebay for about $30 after mine ripped. It's not being reproduced as far as I know.

Anyone have a print of how the vacuum operates that heater core cutoff valve?

HUGE thanks to all the contributors to this excellent thread, especially to the guys posting photos. Today, I removed the wipers and cowling, removed the vacuum hose from the fresh air flap vacuum diaphragm, spliced it back onto the black/orange vac hose behind the glove box, and then pushed the repaired hose back through the interior firewall. Hooked the hose back onto the vac diaphragm, and now have full HVAC flap function. I made my splice using some of the thin walled yellow "Tygon" fuel line that is used for 2 stroke string trimmers (weed wackers). Worked perfect.

75gmck25 said:

On my '75, with the hood open I can remove the screen that is right under the cowl area and I can see that 2nd vacuum motor that is connected to that line. However, I thnk they changed the hood intake arrangement a little in later years.

Is your vacuum line into the engine area connected to a vacuum reservoir, or directly to engine vacuum? There should be a vacuum line from the engine over to the reservoir (shaped like a ball) near the A/C housing, and then the line from inside the truck connects to the other port on the vacuum reservoir If you are running directly off engine vacuum you are probably not getting very good vacuum to the A/C system most of the time.

The vacuum motors are also slow to respond. As I change dash slider positions it sometimes takes 2-3 seconds for the motors to respond, and the recirculate air motor may take more like 15-20 seconds. I don't think lubrication will help much.

Click to expand...

My sphere vacuum reservoir is on the driver side next to the firewall, can I use that one or Do I need a separate reservoir? I have an 86 c10. Not sure if these trucks came with 2 vacuum reservoirs.

The reservoir on the drivers side is usually for the cruise control. The HVAC reservoir is on the passenger side, very close to the blower motor. It might be ball-shaped, or some are more like a cylinder (mine looks like a short, black plastic 3 lb coffee can).