Heater vacuum control switch (Repair Tip)

[243]

Is this switch available new, and if not, is it rebuildable?

[FSJ Guy]

Ummmm.... For what model year???

And exactly which switch?

If you put your FSJ's specs in your signature file, that will save you from having to type it out each time. :- )

[243]

Details details...'78 Cherokee NT, 360/T400/QT TBI Injected

I am referring to the heat/defrost switch.

[letank]

Details details...'78 Cherokee NT, 360/T400/QT TBI Injected

I am referring to the heat/defrost switch.

sometimes one of the screw(s) holding the support for the frame of the control switch on the back of the plate is (are) loose or missing. The result is the impossibility to keep the any position locked.

[Tatsadasayago]

Years ago I opened one up to see what was inside. IIRC there was a rubberish gasket and a wiper that diverted vacuum.
I scanned the gasket and printed a copy of it. I found the appropriate rubber gasket material, wetted it and placed the paper onto it. This left an ink pattern on the material which I then carefully cut out.
The switch worked like new and probably still does after 20+ years.

As far as replacements, I am unaware of any to be had.

[243]

It won't divert the vacuum, I bet that seal is toast. Thanks

[Tatsadasayago]

If the buttons aren't staying pushed in it's a mechanism issue. Cleaning the arms, springs and races then dosing with penetrating oil usually solves this.
Without looking at mine, I can't remember if the switch was held together with rivets or screws...

[Cheap Hobby]

If the buttons go in but don't hold it is mechanical. That was my problem from sitting so long, 15 years. Lubed the pivots grabbed the bar with the pivot points, wiggled a bit then gently rotated bar down. Got it moving nicely and properly.
If buttons move and lock then go for the gasket replacement.

[67GMC]

X2 on this-I had the same issue. Heat button would stay in but Defrost wouldn't. The valve needs to rotate when the button is pushed in. I lubed it with silicone lube (lots) and then gentle nudged it back and forth. Eventually, it rotated and works perfectly now.

[243]

This was a real mind bender, I have worked on it since noon and my last effort was successful.

An hour ago I was ready to go to the pet store and buy an air valve for an aquarium pump and screw it to the dash

Pretty simple switch, one vacuum port and two to pulling the defrost and heater actuators. I had the switch apart at least a dozen times and could hear a slight vacuum leak but it was not pulling even 1Hg on the gauge. I could not see any way that the switch had a gasket because I could see wear marks between the two halves. I tried polishing with Mother's aluminum mag polish, adding a film of grease and nothing worked.

When I pulled the cluster out I used a spring punch to mark the hose ports. I began to think this might have cause a high spot to form so I took a fine flat file and rubbed the area near the pings and noticed a shiny spot.

So I took valve grinding compound and lapped the two halves, then I took 2000 grit wet/dry paper and polished each halve on the glass stove top. I put a fine film of grease on one side and reassembled it. I fired up the engine, connected the lines and it SNAPS those actuators faster than ever.

So, if you peen the valve with a spring punch to mark the hoses this is how you make the repair

[Tatsadasayago]

Interesting!
Mine had a thin rubber-ish gasket that was paper thin.
Excellent tip with the lapping.

[Nikkormat]

The one I took apart (from a 78) was sealed using something similar to antiseize compound and the flatness of the surfaces.

PS: Adding some oil to that felt disk is all it took to fix the one in my 74.

[crisp90]

I have also this query and happy to find the exact same here.

[mx71]

My problem with this was two fold, may tri fold. First, my buttons didn't stay in, so I lubed the mechanism and that was fixed. Then, I couldn't switch from dash to floor, and what I did there was sand the vacuum valve with 6000 grit then place some grease on it. After applying the grease, I cleaned out the passageways with a paperclip. Also, one of the vacuum hoses wasn't connected, so I tested and found which vacuum hose went where, and connected them in the correct places. I don't recall the positions off hand, but a vague drawing of it is in the TSM. Then, I fixed all my emissions stuff and it stopped working, and I realized that I accidentally disconnected the vacuum line from the ball, so I did that and it still didn't switch very positively. I then replaced the vacuum line from the ball to the heater valve/switch and it works great now. Lots of little problems with this one, and it would have been great if they just operated this mechanically instead.