4 seasons heater/ac dash control

[willy12844]

I had to pull this control to replace a broken lever, I noticed on the top left side in the back is a 3 port valve that has one port blocked and no hoses connected to the other 2 ports. This valve is activated by movement of the top lever and by the middle lever when moved to the far right to heater. the ports look like they accommodate 1/8" ID hose, there were no hoses connected to it.
Can someone tell me what it is and what I need to do with it?

Thank You,
Bill












































ate

[dmjlambert]

I'm doing some work in this area also. I believe the idea is the 3 port valve is where you apply vacuum to one port, and get switched vacuum for the water valve and vent/recirculate door actuators. Here is the routing diagram from the service manual for 1969 page 1A-32.

[willy12844]

Good Evening dmjlambert
I had to back away from the trek for a few weeks for a knee replacement, but am back at it.
You were kind enough to send me this drawing and mentioned that you Were up against trying to figure out what it’s all about. If you’ve had any success please share it with me. I’d really appreciate it. They wern’t Hooked up when I took it apart so i’m Not sure what to do.
Thanks,
Bill

[dmjlambert]

I did have some success. I went up to the car parts store and got some 3/16 vacuum hose. It ended up being too big to fit through the firewall grommet. So I went back up there and got some 1/8 hose. I hooked it up according to the diagram and it does appear to work. The control head switch in the diagram I believe is showing a top down view. My door actuators do not work very well, but I can tell they are trying to move. I need to do some cleanup, lubrication, replacement of return springs, etc.

[willy12844]

Question.. does this vacuum valve pertain to AC only? The AC doesn’t’ work but the heater has worked fine ever since i’ve Had the truck. Actually speaking AC is next winters project. If that’s the case i’ll run The hoses from the valve through the fire wall and tie them off til then. I can’t find all the connections under the hood but have to much other stuff to finish her by mid-April. I’m going to file our correspondence so maybe I can get back to next winter.

[dmjlambert]

If you have a vacuum controlled valve on the heater hose from the water pump, then it would switch the valve on (open for water flow) and allow heated air when the top slider on the controller is NOT all the way to the left to inside air. You can verify that is the behavior yours is giving, and if it is not, troubleshoot by disconnecting and plugging the vacuum line that operates the water valve, or connect it to a full-time vacuum source. If the valve opens and shuts OK by heating the air or not heating the air, then move on to figuring out the connections to the vacuum control head on the A/C panel. Probably a vacuum gauge would be useful to do that, but a certain amount of troubleshooting could probably be done by listening and feeling for vacuum with your finger.

I recently bought a Chevrolet chassis service manual, and found it to be good reading. I recommend getting one, they are reasonable in price, about $20 to $35 depending on whether you get it used or new.

[dmjlambert]

A less wordy answer is none of these vacuum connections are essential. The vacuum controlled water valve can be removed/bypassed or hooked up to full time vacuum source. You may not care about switching between recirculate and outside air.

[Rufas]

Originally Posted by dmjlambert

A less wordy answer is none of these vacuum connections are essential. The vacuum controlled water valve can be removed/bypassed or hooked up to full time vacuum source. You may not care about switching between recirculate and outside air.

If you have working AC then having the ability to recirculate the cab air greatly increases the cooling capacity of the AC on very hot days.

[willy12844]

I do have a 1972 Chevy chassis manual and use the heck outta it. I guess what threw me for a loop was when I pulled the control unit out from the dash I saw the valve with no hoses attached to it. Yet my heater had worked fine. Also the one outta my truck has 3 nipples on it and my manual show a pic of it with only 2 nipples. I think I’ve with all your help now have it sorted out.
Thank you for your help,
Bill

[davepl]

Originally Posted by dmjlambert

A less wordy answer is none of these vacuum connections are essential. The vacuum controlled water valve can be removed/bypassed or hooked up to full time vacuum source. You may not care about switching between recirculate and outside air.

Or, another way to look at it is that if you make them all the vacuum doors work then your entire AC system works like a new truck.

That's what I did. I had some trouble figuring out that 3-port valve because it's a 2-port in some years and works backwards in 70 from 71, or something like that (the heater control valve changes with it).

Now mine works like new. Cold air, recircs when I want it, goes where I want it, I can even get cold air out of the heater vents if I want.

Don't abandon something just because it's hard, make it work, it's worth it!

----

PS: Hooking your water control valve up to full time vacuum will shut your heat off entirely on certain years, so don't do that unless you know which years. I forget.

[Rufas]

Deleted.

[willy12844]

I now have myself in a quandary, I’m putting the 4seasons heater control back in, and have all 3 cables hooked up to the control. My problem is I can’t remember where the other end of the temputure control cable hooks to. Please help.
Thanks,
Bill

[dmjlambert]

Engine compartment side of firewall at the evaporator box.

[Mike (Asheville)]

I found this thread hugely helpful when I refurbished by control panel, cables and hoses:

http://67-72chevytrucks.com/vboard/s...control+vacuum

My 72 K20 has a 3-port panel but employs the 2-port setup (as illustrated in the first diagram). If that applies to yours, just make sure to cap the 3rd port to avoid a vacuum leak when the levers otherwise have it open.

I used some vacuum hose and my own lungs to determine which 2 ports to use.

[cebra]

Not to highjack, but I got this far and know where the cables go but I don't know which length of cable goes to which. Does the short one go to the defroster or to the outlet selector? I for some reason marked it to the outlet selector but it is tight and the defroster is a lot longer (make a big loop).

[KSCHEVYUP]

Cebra
You never did get an answer on your question so I'm going to bump this up and see what happens.
I am reinstalling my a/c cables and this time and it has been a long time since I took it apart and I didn't mark parts like I should.
Hind sight is a wonderful thing?
Ron