Vaccum leak for the heater

[Red 1989 MJ]

Take a 20 min. ride with my 89 truck yesterday.

 

Put the heater on, blowing hot air.

 

After driving a couple of minute the air stop coming out, I release the gaz pedal and the air come back.

 

Do you have any suggestion were to begin my search? :dunce:

[ParadiseMJ]

Check all the vac lines along the passenger side fender and under the battery to the vac cannister (reservoir) behind the bumper. Sounds like you have a small leak, most likely a cracked/corrded vac hose. As in, some vac is working there when you are off the gas, but not enough under load (a little leaking out).

 

Very common for those hoses to have a break. Replace the offending hose.

[Red 1989 MJ]

Is the cannister on all model ? :brows:

 

My Comanche don't have any option. (no Cruise, no A/C)

[ParadiseMJ]

Is the cannister on all model ? :brows:

 

My Comanche don't have any option. (no Cruise, no A/C)

 

I believe they all came with the reservoir to at least run the HVAC system. You could just have a ball, my MJ does, but mine also has A/C. Still needs the vac res to open/close the doors. Previous owner may have removed it!!? It's IN the front bumper.

[mjtjnj]

Is the cannister on all model ? :brows:

 

My Comanche don't have any option. (no Cruise, no A/C)

 

I believe they all came with the reservoir to at least run the HVAC system. You could just have a ball, my MJ does, but mine also has A/C. Still needs the vac res to open/close the doors. Previous owner may have removed it!!? It's IN the front bumper.

 

I have the same problem, vacuum lines look good on mine. Someone said that canister can go bad, too....are they still available??

[HOrnbrod]

They can go bad, but it's usually the internal check valve that sticks. Any vacuum canister will work, and why the XJ/MJ engineers put the damn thing behind the front bumper I'll never understand. I mounted a

new one from a Porsche inside the engine bay and got rid of all that leak-prone vacuum hose. Here's the writeup:

 

http://www.comancheclub.com/forums/viewtopic.php?f=9&t=17120&hilit=vacuum

[Red 1989 MJ]

Thanks guys :wavey: