Where is the vacuum cut-out switch located on a 90 Cherokee?

When I have the heater control selected to "vent" the flowing air will alternate between the dash vent and the defroster vent depending on engine load.

 

Not sure what you mean by vacuum cut-out. Your symptom indicates a vacuum leak. High engine load yields low vacuum, like when climbing a big hill or accelerating while towing. Once the vacuum bleeds off, the vents default to defrost.

 

I thought there was a vacuum cut-off switch to turn off the a/c when I floor the accelerator.

 

That would be a compressor cut out all that does is turn off the A/C compressor and does not change the vents . The 1st thing to check is a one way vacuum check valve to make sure that it is good , if that is good then you have a vacuum leak in the system ,

 

I followed all of the vacuum lines and there were no in-line check valves.

Where would it be installed?

 

On a 1990 I don't know were it is , on my 2001 it is at the fire wall on the passenger side . maybe some one who has a 1990 will tell you were it is .

 

You might check that the vacuum reservoir behind the passenger side front bumper and the line to it are intact. Not uncommon for them to break loose and need some zipties or other creative means to reattach them. See this thread. https://www.cherokeeforum.com/f2/vac...roblem-142261/

 

 

Thanks Cruiser54 for the diagrams.

The large vacuum supply line connected to the intake manifold on my 90 XJ does not have a check valve.

I checked all of the parts store web sites and no one listed a check valve for my Jeep.

Being a generic part does anyone have a part number for one with the correct sized hose nipples?


EDIT: never-mind I found one: Doorman check valve 47170

 

Mine doesn't either. There is likely a leak in the piping from the vacuum ball to the firewall.

 

For the Renix models, there's no check valve unless it's a diesel.

Assuming you still have the heater valve, check the vacuum line going to the valve as well.

 

Line is usually corroded behind the battery or the reservoir in the bumper is cracked.

 

Thanks to all who advised that I had a vacuum leak somewhere.

It turns out that the vacuum diaphragm on the heater control valve was leaking vacuum.

Everything now works as it should.

 

I would eliminate that vale altogether before it self destructs and you're leaking more than just vacuum.

 

I just replaced it with a NAPA part.

What would you suggest I put in its place?