When ever my XJ starts an incline the AC will switch from the front vents to the defrost vent. Stumped as to why this would happen, declines and flat lands no random switching only does it when Im Heading up a hill. I can manually switch between the two no problem.

Anyone have any ideas why this is happening and what I could check to fix it?

 

Vacuum issue check the lines especially to vacuum ball behing bumper.

 

X2 Check vacuum lines when not enough vacuum it defaults to defrost

 

Sounds good, I'll give it a look at this weekend. Thanks!

 

Look specifically at the check valve, if it's bad you'll lose your vacuum reserve under load.

 

Got around to looking at my lines today and they all seem in good shape. Where would I find the "check valve"? Could you possibly post a link to autozone or rockauto, etc for it if its not asking to much. I honestly have never dealt with a check valve so I have no idea where to start.

 

Vacuum ***** behind bumper pass side the check valves for its internal.

 

This should help. "Looking good" isn't enough. Probably split behind the battery.

 

thank you so much for the diagram, EXTREMELY helpful!!!

 

On my '91, I have a check valve in a line coming off of the intake manifold on the driver's side. It's only about 3 inches off the manifold.

 

You may wanna go ahead and relocate the reservoir to the engine bay passenger side rear.

 

I pull extra check valves off XJ's in the junk yard when I see them...ususally just pennies. Basically, you should be able to suck air through toward the engine side but not blow it back the other direction.

My MJ did the same thing. Turned out it was a combination of couple of things. It did in fact have a bad check valve, but it also had a split vacuum line.

 

You're welcome. tee hee

 

Check the rubber grommets too. They can look good but crumble when you go to touch them. Ask me how I know this one, LOL

 

My 94 zj does the same thing when going uphills