My HVAC vent control switch is broken. Long story short, I'm certain this is the problem. I see these options:

1. New Genuine AC Delco part 84793087. $220
2. Used version of the above from a junkyard, $30
3. Dorman aftermarket part 299-217. $50
4. Try to disassemble and repair the existing module, part 23283455

Do any of you have experience with the replacement options? I see some reviews online saying the Dorman is a piece of crap and others saying it is fine. Obviously the OEM is not that great either or else it wouldn't be broken which makes me hesitant about a used one. Alternatively has anyone ever successfully disassembled this thing and made it work better?


The long part of the story:

There are like 10+ youtube videos out there promising a quick fix for this problem. Based on all of these I have:
1. Replaced the 7/32 vacuum line from the passenger side intake manifold to the check valve (it was dry rotted and literally broken in half)
2. Tested the check valve (it works fine)
3. Replaced the 5/32 vacuum line from the check valve to the vacuum reservoir under the battery (it was also dry rotted and leaky)
4. Secured the little vacuum line connector thing in the passenger side foot well (some of the hoses were a bit loose)

After the above I was left with a partly working switch (some of the modes kind of work but not others) and a loud hissing sound from behind the switch assembly when one of the non-working modes was selected, so tonight I:

5. Pulled the dash and checked all the vacuum hose connections. None of them are loose and none of the hoses are leaking.

If I push down on the vacuum switch **** from the front, or sometimes the back panel of the switch from behind, the hissing noise reduces a bit and the switch works slightly better (I get one more working mode) but it still is quite dodgy.

 

An update in case you're interested: last night I took the thing apart to see if there's anything I could fix, and it turns out there is a little rubber (silicone?) gasket looking thing with maze-like channels on one side that redirects the vacuum to the door actuators for each ventilation zone. It looks kind of like the valve body inside an automatic transmission. It seals against the switch mechanism with some sort of grease and pressure from a spring. The grease on mine seems kind of thin and sticky. By adding extra pressure with my finger I was able to make it seal properly and could make every vent position work. This morning I went by the hardware store and bought a tube of silicone/rubber-safe Danco waterproof grease. Going to apply some of this and see how it goes today. Might also try to stretch the spring out to increase the pressure if the grease alone isn't enough.

 

@n0p3 Report back on result. I'll bet it's fixed. I always find great satisfaction in fixing things that most would discard. Very helpful as I have vehicles from '68, '85 and '93

 

Keep us updated. I'll bet you fix it. I haven't had an issue with mine but I'd probably be right there taking it apart too. Post a few pics. Maybe one of us will have some ideas.

I haven't heard of these failing much. If it can't be fixed I would think finding a newer one in a junk yard would be good. If you have a U-Pull-It yard in your area it might only be a few dollars if you can find one.

 

Did as I said above and sure enough, it works. There is always a hiss when I change vent modes, and for some modes it is longer than others, but it never does that for longer than a second or two before the vent changes and stays set.

Was the fix a success? Depends on how you measure success. Quick (about 30 minutes), cheap (about $6), and fully fixed the problem? From that perspective- a success. But then again I didn't have to buy any tools to fix it. So from my tool chest's perspective, a disappointment, perhaps?


Procedures? Bah. I'm not paid by the hour. Minimum disassembly is the name of the game. Only have to pop it out, don't have to remove it entirely - and importantly, don't have to unplug any wires.

Single screw to remove with a 7mm socket

Pull back the control assembly for access

Pop off the back of the switch (there are 4 clips holding it in place). Note the gasket valve body thing. What is that thing called anyway?

Adding the grease. How much am I supposed to add? No idea. How much did I add? SOME. See picture. Spread it around, reassembled everything, and...

Success! It works now and another quality-of-life issue with this van solved. Zoey doodles approves.

 

Very cool. Not too different from the control head on my pool filter that changes it from filter to waste or backwash etc...

The hiss when changing modes is normal. Looks like you fixed it 100%. One way to make sure it's holding vacuum is to come to it after it's been sitting for a while and change settings while the engine is still off. You should hear the hiss for at least the first change.

 

Well, the saga continues. I TLtook the van on a road trip across the state this weekend and noticed that the selector would still have the old problem when it was cold out and the engine was cold. Once it warmed up it would work better. This is North Carolina so we're not talking crazy cold. Upper 20s at worst. But the difference in performance was quite noticeable.

Is the vacuum from the intake weaker when cold? Is the the gasket valve body thing less flexible when cold? Does the grease thicken up and not seal as well? Does the check valve work better when warm? Do I just need to replace the spring with something stiffer? Will have to take it back apart to find out.

 

I need to dig into the root of a similar issue on my side. When going away from full cold and going to any bit of heat at all on front control (I have a passenger van with rear HVAC) I can hear that the vacuum noise in the dash never stops. Everything works so I haven't dug into it more but I eventually will need to. I suspect it could be the vacuum going to the heater bypass valve or the heater valve itself. I haven't researched when vacuum is applied to the heater bypass valve but it is another possible hidden vacuum line that could be leaking.

 

Follow up on this one, when cold weather hit, the problem came back. I bought the cheap aftermarket replacement HVAC control module. The vacuum switch worked 100% - but the blower speed control switch was somehow DOA. Not wanting to deal with a return, I took the vacuum switch part of the assembly from the cheap aftermarket unit and put it on the factory control module. Reassembly was a bit tricky - there was a ball bearing that was kind of finicky to get back into place, but everything fit, and after doing this I can say for certain that everything is working as it should now.

 

Good to see you got it working.

This thread really helped me a few weeks ago. Not long after reading the OP I started noticing a hiss when driving that was throttle related. It would come and go but was strongest when the engine vacuum should be high so I figured it was the switch. I used your pics to take it apart and grease it. I used some thick dielectric grease I had on hand. No more hissing.