Here's some data pertaining to the 97+ XJ Vacuum Sytems, as taken from the 2000 FSM.

HVAC SYSTEM (Section 24 FSM)

VACUUM CHECK VALVE

DESCRIPTION
A vacuum check valve is installed in the accessory vacuum supply line in the engine compartment, near the vacuum tap on the engine intake manifold, and at the HVAC unit takeout. The vacuum check valve is designed to allow vacuum to flow in only one direction through the accessory vacuum supply circuits.

OPERATION
The use of a vacuum check valve helps to maintain the system vacuum needed to retain the selected heater-A/C mode settings. The check valve will prevent the engine from bleeding down system vacuum through the intake manifold during extended heavy engine load (low engine vacuum) operation.
The vacuum check valve cannot be repaired and, if faulty or damaged, it must be replaced.

VACUUM RESERVOIR

DESCRIPTION
The vacuum reservoir is mounted to the front bumper bar behind the passenger side bumper end cap. The bumper end cap must be removed from the vehicle to access the vacuum reservoir for service.

OPERATION
Engine vacuum is stored in the vacuum reservoir. The stored vacuum is used to operate the vacuum controlled vehicle accessories during periods of low engine vacuum such as when the vehicle is climbing a steep grade, or under other high engine load operating conditions.
The vacuum reservoir cannot be repaired and, if faulty or damaged, it must be replaced.

SPEED CONROL SYSTEM (Section 8H FSM)

VACUUM RESERVOIR

DESCRIPTION
The vacuum reservoir is a plastic storage tank connected to an engine vacuum source by vacuum lines.

OPERATION
The vacuum reservoir is used to supply the vacuum needed to maintain proper speed control operation when engine vacuum drops, such as in climbing a grade while driving. A one-way check valve is used in the vacuum line between the reservoir and the vacuum source. This check valve is used to trap engine vacuum in the reservoir. On certain vehicle applications, this reservoir is shared with the heating/ air-conditioning system. The vacuum reservoir cannot be repaired and must be replaced if faulty

VACUUM SUPPLY TEST

(1) Disconnect vacuum hose at speed control servo and install a vacuum gauge into the disconnected hose.
(2) Start engine and observe gauge at idle. Vacuum gauge should read at least ten inches of mercury.
(3) If vacuum is less than ten inches of mercury, determine source of leak. Check vacuum line to engine for leaks. Also check actual engine intake manifold vacuum. If manifold vacuum does not meet this requirement, check for poor engine performance and repair as necessary.
(4) If vacuum line to engine is not leaking, check for leak at vacuum reservoir. Disconnect vacuum line at reservoir and connect a hand-operated vacuum pump to reservoir fitting. Apply vacuum. Reservoir vacuum should not bleed off. If vacuum is being lost, replace reservoir.
(5) Verify operation of one-way check valve and check it for leaks.
(a) Locate one-way check valve. The valve is located in vacuum line between vacuum reservoir and engine vacuum source. Disconnect vacuum hoses (lines) at each end of valve.
(b) Connect a hand-operated vacuum pump to reservoir end of check valve. Apply vacuum. Vacuum should not bleed off. If vacuum is being lost, replace one-way check valve.
(c) Connect a hand-operated vacuum pump to vacuum source end of check valve. Apply vacuum. Vacuum should flow through valve. If vacuum is not flowing, replace one-way check valve. Seal the fitting at opposite end of valve with a finger and apply vacuum. If vacuum will not hold, diaphragm within check valve has ruptured. Replace valve.

 

Why did you post that it's "unrelated to the HVAC system", then? Lol

 

By the way, that article that says it cannot be repaired...it's wrong.

I saw someone wrap it in electrical tape to fix it.

 

Found this data in the FSM after I looked in the parts catalog.

I'll have salt and pepper on my Crow please.

 

I fixed mine. It was just hanging behind my bumper and both mounts were still bolted to the bumper. I took the mounts off the bumper cleaned everything up and JB welded the mounts back on to plug the holes in the can back up then relocated the can up under the coolant overflow bottle. It works just fine and has been for months now.

Black89

 

Franks goes well on crow. I know first hand.

 

But wait you rocket scientists...

What about XJ's without cruise control. Does this mean the HVAC system will not work properly if the Speed Control Reservoir is not installed?

I know the answer...nanner nanner nanner.

 

The info posted says that the ball is there for when there isn't enough vacuum generated by the motor. So I'm guessing it's just a backup.

 

Har har

 

Did something go over my head?

Its been a long day.

 

I think Ken had a derp.

 

 

I've heard of blue *****....