Vacuum System / Heater Control Airflow

1987 I6 AW4, no cruise, no a/c, My beater XJ I grabbed the D44 from.

Common problem I know. Searching various forums hasn't solved this yet. But from what I read and what I can deduce from the FSM: Fan speed / blower / vac resevoir / heat-cool all works. System is simply stuck on defrost so this mean no vacuum (NV).

BIG QUESTION. Does this sound right...I have two lines coming from the vac resevoir in the bumper. ONe big. One small. The big one goes only to the intake manifold (there is a place for a t-connection but it is capped off. The small one goes about half way but stops under the coolant resevoir and is open. Are these not supposed to connect somehow into the firewall?

From looking at the spare parts the previous owner had I'm wondering if he tore some lines of the vac line coming from the resevoir / going to the door controls.

AND...Before I tear into the dash can I check for leaks anywhere else under the hood?

TIA

There certainly should be a vacuum line coming out of the firewall for the heater controls, and you should have some kind of vacuum line going to the heater water valve too. Is there anything connected to that? I'm guessing that the line that goes through the firewall got pulled out, and you'll find an orphan connection under the dash which will then lead to the heater control, and branch from there to the various flappers and the heater valve. You may have to rummage down at the canister end to see what's connected where, and whether it's a one or two chamber reservoir (my cruise-equipped 87 had a double, one side for the heater and axle motor, the other for the cruise). A vacuum gauge would help to find out whether there's any vacuum present at the dead-end line, but you ought to be able to feel it with engine running.

Thanks for replying.

Matthew Currie said:

There certainly should be a vacuum line coming out of the firewall for the heater controls,

Click to expand...

The only ones I noticed were on the driver's side and not connected (that I could tell) to the main one from the vac canister.

and you should have some kind of vacuum line going to the heater water valve too.

Click to expand...

Is the water valve behind the dash? I believe the FSM shows it but doesn't specify where it is.

...heater control, and branch from there to the various flappers and the heater valve

Click to expand...

all behind the dash, right?

You may have to rummage down at the canister end to see what's connected where, and whether it's a one or two chamber reservoir

Click to expand...

It's just a one chamber. There is definately vacuum there. I can hear it when I pull the line...sounds strong too.

I guess I need to rip into the dash. Oh joy.


Thanks for the help.

ANyone else find leaks elsewhere...behind the control unit...etc?

There should be a grommet (on passenger side firewall in engine bay) with two vacuum lines coming out of them. Left one goes to heater control valve which should be right by coolant bottle (and mounted on a bracket I believe). The right line goes to that vacuum ball.

You shouldn't have to fiddle inside the dash once these lines solve your problem.

You've got vacumn lines running from the cannister(behind the front bumper,passenger side) all the way to the firewall and into the right side of the vehicle.
Check all lines that are touching the body every where,run your fingers along the lines.Anywhere there is a break trim the ends and splice w/5/32 id gasline hose.There are a couple lines that run under the battery tray.
The one that controls the heater has been known to rub against the firewall and create a leak there.
If you have the vac disconnect front axle,make sure the connector is on tight.ANY VACUMN LEAK WILL CAUSE THE SYMPTOMS YOU ARE TALKING ABOUT.Check anything that resembles a vacumn line...any breaks splice w the
5/32"id gasline hose.I used the gasline hose due to the heat in the engine compartment heat,it's braided hose and should last longer.There are places where you can get the hardlines in bulk.
IMOHO..I would check the vacumn lines BEFORE I would pull the dash...