Vacuum Diagram 1978 Wagoneer? HEATER/DEF Question...SOLVED

[Hecdog]

ANyone have a complete vacuum diagram for a 1978 Wagonner? I have the Technical Service Manual (3 volumes) but can't seem to find a complete diagram.

Essentially, my heater/defrost switch doesn't work. It always send air to the lower vents and it drives me nuts. At highway speeds, there's a constant flow of hot air from the lower vent, even with the temp control set to cold.

Anyone have a vacume diagram or now how to diagnose the heater/defrost issue?

I feel vacuum from the vacuum reservoir, but I can't seem to pull of the instrument cluster to test the vacuum switch.

Help??

[carnuck]

Sounds like someone bypassed it at some point. The heat should be off by default unless something is jamming the door open (leaves are common) There is a vacuum right above the gas pedal that gets knocked off, and then it won't switch to defrost. It should have vacuum coming in to the dash switch, then out to heat flapper and defrost. I join the 3 lines together for winter so I have defrost and heat at the same time.

[Hecdog]

How do I check the door?

When I press the defrost button, it doesn't stay pressed it just springs back out to neutral. The heater switch does stay pressed, and resets when the off button is pressed.

I just went out there and checked it as best as I could. Essentially, I stuck my hand behind the cluster and pressed the defrost swictch manually, but I feel no vacuum coming to the defrost hose--there's a hose coupler in the defrost hose right before the defrost vacuum switch). If I suck on the vacuum hose, I can hear the switch working and feel the air diverting to the windshield. But, there seems to be no vacuum coming to that hose from the dash switch, even if I press the switch manually. Does that switch go bad, the one in the instrument cluster?

ANother curious thing--if I turn off the engine, and turn on the fan, the fan blows but no air comes from the lower vent or upper defrost vents. But if I cut on the engine, air starts coming out of the lower vents--not the defrost vents. This must be why I feel hot air coming out at highway speeds even with the fan off. A vent door must be opening with the engine on, allowing outside air to come through the lower vent. The question is, why is it hot, with the control on the cold setting?

[carnuck]

Someone hooked the flap directly to the vacuum from the motor.

[Hecdog]

Thanks! But how do I check that? Where is the flap so that I may reset it?

[carnuck]

Someone recently posted a pic of the vacuum stuff behind the dash. Mine is 50 miles away so I can'tg et pics.

[tgreese]

ANyone have a complete vacuum diagram for a 1978 Wagonner? I have the Technical Service Manual (3 volumes) but can't seem to find a complete diagram.

...

Did you look in section 13, "Heater and Defroster?" In my '77 manual it's figures 13-2 and 13-4. Not much to it... should be clear from the drawings.

[Hecdog]

Yes, I saw section 13. I'm going to take another look today. Although the drawings seem clear, I can't seem to find the components under the dash. I think I'll have to remove the AC unit to get a better look. As far as I can tell, the 3 vacuum hoses are connected to the dash vacuum switch. It's almost like that switch is stuck in the heater position, no matter which push button is selected.

In addition, the weird thing is that HOT air comes out at highway speeds even if the temp control is set to cold.

[pcoplin]

MIne did that when I got it. The selector was sort of rusted. After taking it out and spraying some PB blaster on it, I got it to free up, now it works great.

[Hecdog]

Thanks, I figured it out. Essentially there were 2 problems.

1. At highway speeds, hot air comes out of the lower heater vent. This was due to two problems: The first issue was the vacuum switch would not turn off (see #2 below) and the second issue was the cable that opens and closes the vent door to the heater core (in the engine bay) was not affixed to the firewall and would move when operating the heat/cold slider. This would prevent the door from closing all the way. any air coming through the lower vent was always hot since the door to the heater core would not close. I affixed the cable to the firewall and that allowed it to close properly. Fixed!

2. The second problem was that the Off/HEat/Defrost switches were not working. Air always came out of the lower vent and no button would operate properly. Only the "heat" switch would stay depressed. The other two buttons (off/defrost) would simply spring back out. This was a trickier problem to solve. After checking that all vacuum hoses were connected and that there was vacuum at the reservoir (in the engine bay) I noticed that when a switch is pressed there's a swiveling bar that rotates the vacuum control switch behind the dash. There's a second bar at the tail end of the switches that "catches" a switch when the switch is pressed. The tail end of the switch lever has a notch, and the "catch" is spring loaded. WHen you press a button, the "catch" lowers a bit and when it finds the notch in the tail end of the switch lever, it springs back up and catches the switch lever and holds the switch in place. When a second button is pressed, that lever moves the "catch" down, which releases the first button and "catches" the second button. In addition to this simple yet clever button catch mechanism, each switch lever rotates a swiveling bar via an angled flange. There are 3 levers, attached to each button, each with a different angled flange in the middle of its lever. When a button's flange hits the swiveling bar, it rotates it to the angle set by its flange. This angle is IMPORTANT, because the swiveling bar rotates the vacuum control switch into one of 3 position, which correspond to OFF/HEAT/DEFROST.

This is how that mechanism works. As a button is pressed, it rotates a swiveling bar which in turn rotates the vacuum control switch, which then diverts the vacuum to either the HEAT vacuum motor or the DEFROST vacuum motor or OFF (vacuum is cut off).

The problem I was having is quite simple. Behind the instrument cluster, on the top left, theres a screw, about 1 inch behind the instrument cluster. You can see it when you remove all the screws from the cluster and pull it slightly outward, toward the cabin. On my cluster, this screw was missing. That screw holds the entire mechanism that I described above together. That screw attaches it to the cluster and holds it rigid. If that screw is missing, when you press a selector button ,the entire control switch mechanism moves slightly, it doesn't hold it rigidly. This little movement causes the delicate, well coordinated "catch" and release type mechanism to fail. The switches never find the "catch" bar which in turn never rotates the swivel and then the vaccum control switch. It's a delicate dance. Once I replced the screw, it worked perfectly!!!

Sorry for the long write up. I figured there might be someone else out there who might run into this issue and find this solution helpful.

[Livendablues]

This is great info. My vacuum hoses were all disconnected, is there a certain way they are to be connected to the push button vacuum switch?
Thnx in advance.
John