Vacuum Issue for AC system

XJ-S
1

Alright guys I need a nudge in the right direction here. 1995 XJS 4.0 2+2 LHD. I’ve replaced all the ac components in the engine bay. The air is nice and cold now. No issues there. What I do have is vacuum issue however.

When I accelerate the actuator that directs the blowers to the dash vents is losing vacuum. I have located the vacuum reservoir behind the passenger knee bolster. Looking at the diagrams I have found on here, I believe that I have a bad check valve on the line going out to the engine.

So two questions -
Does that seem like a reasonable diagnosis to start with?
Does anyone know where that check valve is located? I’ve been all under the dash and can’t seem to find it.

I have fixed so many things on this car based on reading past threads, but this one I haven’t found much content on.

Thanks

2

The vacuum check valve is located on the engine side of the firewall, you will need someone with the 4.0 AJ16 to tell you exactly where it is. You may be able to spot it just by looking at the vacuum lines coming out of the passenger side firewall and going to an engine vacuum source.