Just an FYI, I know this has been covered. But my new to me 1988 XJ (this week) had an issue with the vent air only blowing out of the defroster vents.

Per suggestions I found here, I started chasing down the vacuum lines. Found one line broken where it goes through the header panel (going through to the canister). I fixed it but the issue persisted.

Pulled the canister out from behind the bumper. Found 3 or more other vacuum line issues. Some lines broken, some deteriorated. Did a temporary repair on them and viola, air handler working as it should.

I went ahead and relocated the canister under the coolant reservoir, fixed the line issues and all seems to be functioning as it should. Now it is much more accessible if any future issues arise. Not to mention not near as much vacuum line to have issue with.

Thanks to the info on this forum I was able to go right to the issue and resolve it..

Now to see why the A/C is not blowing cold... I found the A/C power wire to the compressor was severed. I repaired it and compressor/clutch comes on but no cold air... Looks to have a R134 fitting so it has apparently been converted. Will probably grab a can of freon and see what happens.