Heater/Defrost Vacuum Switch

[mx71]

79 Wagoneer with the 360:

None of the vacuum lines for the heat/defrost switch were hooked up and the heat button wouldn’t stay down. Lubed the assembly and the heat button now stays down. Hooked up the lines and the heat won’t switch from floor to dash. I manually put the engine vacuum line on each of the tubes and it did switch to the dash.

1. Does anyone have a diagram of the order the lines get hooked up in?
2. I see where the floor line goes to that floor valve, but where does the defrost line run to?
3. Is my switch bad? Why isn’t it switching?

[fulsizjeep]

There is heater control info starting at section 3D-6.
http://oljeep.com/gw/79_tsm/79_Jeep_TSM.pdf

[mx71]

Yeah, it's pretty vague.

[tgreese]

Seems pretty explicit to me. 3D-7

"Installation"

(6) Connect vacuum hoses.
(a) Number 1 on vacuum control switch goes to
defroster vacuum motor.
(b) Number 3 on vacuum control switch goes to
vacuum storage tank.
(c) Number 4 on vacuum control switch goes to
air inlet door vacuum motor.

Fig 3D-6 shows the vacuum motors. The tank is under the hood.

Test switch function in situ or on the bench with a MitiVac.

The TSM is written for the line mechanics (techs) at the dealership, so it won't teach you skills they are already expected to have.

I recall some have taken this switch apart, cleaned lubed and reassembled. Search old posts here ot at IFSJA and you may find something about it. No service parts are available - replace if necessary. Should be easy to fix if broken since it 1) seems to never wear out , and 2) every one of these cars has one.

[mx71]

Which is #1, which is #3, and which is #4?

[tgreese]

I would assume it's marked on the switch. If not, you should be able to infer which port connects to which function by test.

Pull the cluster out of the dash.

[mx71]

It is, sorry! I hadn't pulled it out. I think I found the problem...no rubber gasket. Is it just a circle with a hole in the middle or is there ports in it?

[tgreese]

I don't know offhand - I have not ha one apart. Search old posts here and at IFSJA. Use Google or Bing, not the native search facility.

https://www.bing.com/search?q=site%3Afs ... tch+repair

[mx71]

I have. Apparently it isn't the most popular issue. This is all I've found and it doesn't show a gasket:

http://www.fsjnetwork.com/forum/viewtopic.php?t=10471

[mx71]

Well, I sanded with 600 grit, cleaned really well, and put some grease on it and it's working! Thanks!

[tgreese]

NP! Glad it helped.

[merrill77]

FWIW, looking at the side with the ports pointing at you, rotated so that all three are in the 10-2 o'clock orientation:

• left: defrost
  center: vacuum source
  right: heater

If you are trying to connect the hoses with it installed in gauge cluster:

• front/lower: defrost
  center/top: vacuum source
  rear/lower: heater

where front/rear reference the vehicle orientation.

Hope that helps someone.