'92 4.0 Stuck in Defrost mode

This is a new to me XJ, so I have no idea if it ever worked, but it seems to be stuck in the defrost mode.

I can move the selector switch but it does not change between floor, vent and defrost mode. It's either off, or just coming out of the top vents at the windshield (defroster.)

The blower motor works in every speed. I have a/c, but I don't know if it works either. It doesn't effect the outcome of what louvers are operating as it stands right now, not even in "bi-level" mode.

From searching, it looks like I have the exactly opposite problem that some of the '97 plus models have, where the defrost door is stuck closed.

I've also heard that the selector switch is supposed to fail into defrost mode should anything go wrong.

I'm thinking it might be a vacuum leak but where should I start?

TIA

check the lines going to the vacuum canister. it defaults to defrost mode when it loses vacuum. the canister is behind the front bumper on the passenger side, it looks like a big pill.

most likely the plastic line going the the tank is cracked or has gotten disconnected.

Can I get to it from underneath, or do I need to remove the bumper?

In general, how do you test for a vacuum leak? I'll start by checking that canister, but is there a way to pressurize or pull a vacuum on any of the lines to check for a leak?

You can try the Stogie test.


Step 1.
Buy a cigar, light it, toke it up.

Step 2.
Remove vac line from firewall. Blow smoke into vac line.

Step 3.
Look for smoke escaping from, well, anywhere.

Step 4.
Fix leak, Replace hose etc.

Step 5.
Put out cigar (save for later).

Thanks. It did turn out to be the line at the "hindenburg." I could get to it from underneath the passenger side front bumper. Some how the line was off.

Thanks for everyone's help.

ParadiseXJ said:

Step 5.
Put out cigar (save for later).

Click to expand...

:idea::idea: