Heat/ac Question 89 Mj 4.0

[ctxj93]

I've been having some issues with the heat in my MJ. It seems like I'm getting very little air out of all the vents even on high. My defrost vents blow like crazy on cold but don't flow nearly as well on hot.

 

I jammed my arm up behind the heater box and can feel that there is a decent amount of air coming out back there even on the defrost setting. Is this supposed to happen? I can't tell if there is a vent back there or not.

I also have a substantial vacuum leak on my intake. I am able to switch between air settings still but it usually reverts back to defrost eventually when driving. Is there a vacuum controlled blend door that might not be opening all the way and in turn causing poor airflow?

[Eagle]

You have a vacuum leak.

 

The vent flapper doors are operated by vacuum. By design, the default when there's no vacuum is for the doors to direct airflow to the dash-top defroster outlets.

[ctxj93]

Yeah I know I have a vacuum leak. But I'm wondering if that's causing low airflow through the vents, As well as not allowing the selector to switch between

[cruiser54]

Yeah I know I have a vacuum leak. But I'm wondering if that's causing low airflow through the vents, As well as not allowing the selector to switch between

That's EXACTLY what Eagle is trying to tell you.........

[Eagle]

 Is there a vacuum controlled blend door that might not be opening all the way and in turn causing poor airflow?

 

Yes.

[ctxj93]

Sweet thanks eagle. I knew that the selector was vacuum controlled I just wasn't sure if there was something else going on in there too.

[HOrnbrod]

The blend door is actually controlled by a mechanical cable. It won't move if the cable clamp is loose. You can stick your head down there and watch the door move (or not move) as you slide the the lever.