ventilation problems

**unit861** · 02-11-2010, 08:01 PM

I have a '96 XJ with 220K miles with a problem in the ventilation (i.e. air vents)-- the air cuts out while the engine is under load (hills, accelerating). This holds true with the A/C on or heat, at any blower speed, and in any position of the vent control slider. As soon as I back off on the gas pedal, the air returns. Can anybody explain this?
Thanks!

**mortalenema** · 02-11-2010, 08:09 PM

Sounds like a vacuum leak.

**unit861** · 02-11-2010, 10:31 PM

Alright, thanks...I never thought of that possibility. I just remembered the one consistent thing is that the air would shift from floor or vent to the defrost vents no matter what position the control was in. Always on hills or accelerating.

Any suggestions as to how to cure this?

99Greenmachine · 02-11-2010, 11:10 PM

I'm not sure that's a Vac leak because if there's a leak, it will be worse at idle rpms compared to cruising rpms...I'm not an HVAC pro though but I thought I would use some logic

Dbiked · 02-11-2010, 11:15 PM

I have this same problem. I always thought that's just how it was. haha so I would be very interested in this. In mine it sounds like the blower is continuing to blow, but the air just isnt getting through. as if the blend door closes for some reason.

themow · 02-11-2010, 11:27 PM

Quote:

Originally Posted by unit861

Alright, thanks...I never thought of that possibility. I just remembered the one consistent thing is that the air would shift from floor or vent to the defrost vents no matter what position the control was in. Always on hills or accelerating.

Any suggestions as to how to cure this?

It reverts to defrost automatically....its a safety thing they all do it in case of a low vacuum situation. It really sounds like a vacuum problem to me. And no vacuum would be greatest at idle not at cruising. Google locating a vacuum leak and you will find some good info its not jeep specific. Also on the 97+ there is a vacuum canister ball up in the bumper in the passenger side...prob on your year too not sure though. Id chekc that first to see if its cracked...theyre plastic ....good luck

polizi212 · 02-12-2010, 12:14 AM

Start at the vac canister in front and follow the vac lines looking and feeling for cracks and breaks! Look under the battery, Mine leaked there, My vac line looked like it was eaten by battery acid I replaced about a foot of line.

Dbiked · 02-12-2010, 01:17 AM

Thanks from me guys. thats some good info.

**mortalenema** · 02-12-2010, 06:06 AM

Quote:

Originally Posted by 99Greenmachine

I'm not sure that's a Vac leak because if there's a leak, it will be worse at idle rpms compared to cruising rpms...I'm not an HVAC pro though but I thought I would use some logic

You actually get less vac with more load on the engine. My '51 Kaiser has wipers that run on a vacuum pump. Speed up and the wipers slow down. It's pretty funny.