I finally took some time to take a serious look at my rear air.
I took some pictures to help explain.
There are a number of components that controls the rear air and heat, and the duct work.
Regarding the rear heat and AC.
In the rear there are two actuators, one inside the passenger compartment, that I posted a picture of earlier... it is attached to the blue lever. It is vacuum actuated with a thin white vacuum line. It gets its vacuum from the switch on the dash. I'll cover that in a llittle bit. The blue lever when in the down position will direct air through the roof vents, when in the up position it will direct air through the side bottom vent. That acutator is spring loaded, and when there is no vacuum supplied, or insufficient vacuum supplied the default position is with the lever in the up position (air flow directed to the floor).
There is also another actuator on the driver's side under the truck that is a vacuum controlled valve. It controls the flow of hot water in and out of the rear heater core. It gets is vacuum supply from the same vacuum line as the inside the car actuator. One line comes from the switch in the dash and is later split to feed both actuators.
On the right side of the dash there is a switch that controls the fan speed, and whether one will get AC or heat in the rear. That is an interesting switch in that it is a vacuum switch, and an electrical switch in one. It has a black vacuum hose supply line, and a white vacuum hose that is affected by the flipping of the switch to determine if the white vacuum hose will have vacuum. That is the white vacuum hose that controls the rear two actuators I mentioned above. It is also an electrical switch that determines the rear fan speed.
Here are some of the steps I took to determine that my problem is a switch that is leaking vacuum.
My symptoms were that sometimes I would get roof air, sometimes floor air, and sometimes heat.
I pulled the inside panel out, and the vacuum hose to the actuator inside the car. I had vacuum, I measured it at 5 inches with a vacuum guage. I pulled the actuator out, and sucked on the vacuum input. It worked and held vacuum. Another suggestion mentioned above is to depress the actuator, put your finger over the inlet, and see if it stays depressed. IN either case, if it didn't hold vacuum, it would have to be replaced.
I crawled under the car and put a hose on the vacuum input for the heater flow control valve, and sucked on it. I heard it move, and it held vacuum. I presume it is good. Now.. I know that I can draw down approximately 16 inches of vacuum by mouth, so I estimate that it took about 10 inches to close that valve.
Now remember that I only had about 5 inches of vacuum out of the white vacuum line. both of my actuators are capable of holding vacuum, so I needed to see how much vacuum my engine was creating.
I started her up and pulled a vacuum line near the intake manifold, and found that I had 17 inches of vacuum at idle. Obviously I had a leak somewhere in the line that feeds the rear actuators.
The connections going to the actuators were like new, and very tight. I decided to look at the in dash controls.
The front panel has about 10 pressure fit clips, being careful, it pulled straight out.
There are four screws that holds the switch panel in place.
And one that holds the right hand switch in place.
The black hose in the back of the switch brings vacuum in, and when the switch is turned to heat, it just blocks the hose so that there is no vacuum leak. When the switch is turned to rear AC, it connects the black and white so that the white has vacuum (which shuts the hot water off from underneath, and flips the blue lever on the inside to direct the air to the roof.)
I checked vacuum at the black hose at the switch and had 17 inches of vacuum. So I knew that I was loosing some vacuum between there and the actuators.
Here's more information than what you need unless you are also having an issue with your front vents. When I just disconnected the vacuum connection to the switch, it created a vacuum leak in the black hose. That hose gets its vacuum from the main black vacuum line that feeds the front vent directional control switch and all of its actuators. When it was disconnected the default was for the air or heat to be directed to the windshield/defrosters.
When I held my thumb over the opening to the black hose, the front vents worked properly again.
I took the switch apart and couldn't figure how to fix it I ordered a new one. TO my pleasant surprise it was only $30 with tax. It'll be in tomorrow, from the dealership.
IF one wants a free bypass, I temporarily stripped about 3/4 inch of plastic insulation off of some 16 or 18 guage wire. Stuck it in both ends of the plastic connector that holds the black and white hoses into the switch to splice the two together, and taped it up with black electrical tape.
When one wants rear heat, pull that tape off, and block the black hose with some tape.
Here are some pictures to help.
RemoveThis.jpg
This just pulls off
FourScrews.jpg
ONly four screws holds this in
VacuumControlSwitches.jpg BlackAndWhite.jpg
This plugs into the rear switch. IF one wants a free bypass, I temporarily stripped about 3/4 inch of plastic insulation off of some 16 or 18 guage wire. Stuck it in both ends of the plastic connector that holds the black and white hoses into the switch to splice the two together, and taped it up with black electrical tape.
When one wants rear heat, pull that tape off, and block the black hose with some tape.
RearHeatControlValve2.jpg
This is the rear heater control valve that is outside, under the van on the driver's side in front of the rear wheel.
Linear Mode
