I recently bought an XJ and now I'm beginning to go through it.

First issue is a poor performing AC system. It doesn't seem very cold, but the first issue is the airflow from the vents changes while driving. Put the engine under a load and the air from the vents drops substantially.

I'm fairly certain that the fan itself is not changing speed, it's just the mechanism that controls where the air is directed. I know this is vacuum controlled so I'm guessing I have a vacuum leak under the hood.

I blew smoke into the intake manifold and had it seep out from the grommets on top of the valve cover as well as the throttle body. It appears to come from around the shaft that the throttle cables attach to and from one of the sensors on the other side. I ordered new grommets, that's easy, but I'm wondering about the throttle body.

Would old seals on the butterfly shaft cause enough of a vaccum leak to cause my problem. There doesn't seem to be a rebuild kit available so I'd need to replace the entire unit. I'm curious if a brand new throttle body would be totally sealed. Anyone have any thoughts? Anything else I should be looking for that could cause this issue?
Appreciate any guidance.

Brent

 

OUR '96 XJ's temp control isn't vacuum controlled. We have a blend door that's cable controlled. Look in front of the passenger seat under the dash against the fire wall and you should see a cable attaching to a lever. It may have come off. Mine was off and the one on my son's '97 TJ also. HOPE that is your problem as it's an easy fix.

 

Lets make this simple.

 

That definitely needs to get looked at also.

 

About the throttle body shaft leaking. There are no seals on that shaft and any vacuum leakage is made up for by the IAC. If the clearances on that shaft are real bad, you'll need another throttle body.

Also, the blend door on the WJ is controlled by an electric stepper motor and not by cable or vacuum. The mode switch is vacuum. I'm not aware of any cables on the manual heater in my WJ. The reason the blend door in WJ's is such a problem is if it binds, the stepper motor doesn't care and just breaks the plastic shaft.

 

SORRY for the mistake (corrected it) in my #2 post. My son's got a '97 "TJ".

 

Replacing the two vacuum check valves on the vacuum lines fixed the air switching to defrost under load for me.

 

Thanks for all the guidance. I found a couple leaks which I fixed. Also one of the check valves is leaking so I ordered one. The air moving away from the front facing vents under load is improving so I’m hopeful the leaky check valve will take care of it. Now another question, is this the ac/heater control? It’s a vacuum operated valve but there’s no vacuum line connected. If this valve never moves, which of course it won’t if there’s no vacuum line connected, what would be the result.

 

That's the heater control valve. They were eliminated from '97 on. Many of us with pre '97s do the same. I've not had mine for years. To do it you can install a set of 97+ preformed heater hoses and just block off the vacuum line that goes to the hcv (when you locate it!). Doesn't affect the performance of the heater or a/c at all. In fact it preferred in that it allows coolant to constantly circulate through the heater core keeping crud from building up.

"is this the ac/heater control?"
No the heat and a/c are controlled by a cable operated blend door.

 

This^^