heater control valve

I just replaced my heater control valve (91 limited btw) --$15 at AZ-- where does the vacuum line go? I don't think it has much if any vaccuum so I'd like to find and fix the problem.
TIA

Merry Christmas!! two weeks to hunt and work on my jeep!!!

I don´t have the schematic (vacume) for the post 90 XJ. But the controls look the same from the outside (pretty much). The heater control vacume lines are usually color coded. The one your looking at probably goes back to the heater control in the dash. In the early models, the large vacume line going from the intake manifold (through a couple of T´s) to the vacume resivoir, would pop off or corrode, cause A/C and heater switching problems, due to low vacume.
There is a vacume plug with multiple vacume lines that plugs into the top of the heater a/c controls that has been known to come loose. I´ve loosened it installing a new radio. Had it work loose while dirt roading.
Maybe somebody with more experience in the post 90 XJ, has some more ideas.
I usually turn the heater on the heat setting, then wet a fingure and hold it over the end of the line, sucks pretty good, when everything is hooked up.

Just out of curosity,does the htr valve have 2 inlets and 2 outlets and is it black plastic?
If it is,then you have the correct valve for the 90'
IF the valve is metal and looks kinda brassy then you have the htr valve for a 84'-89' w/the closed system.
The vacum line plugs into the vacum chamber on top of the valve,the line is one of the really small ones that will break easily so be careful.

churky89 said:

Just out of curosity,does the htr valve have 2 inlets and 2 outlets and is it black plastic?
If it is,then you have the correct valve for the 90'
IF the valve is metal and looks kinda brassy then you have the htr valve for a 84'-89' w/the closed system.
The vacum line plugs into the vacum chamber on top of the valve,the line is one of the really small ones that will break easily so be careful.

Click to expand...

It is the black plastic like the original, the vac. diaphragm is slightly reworked but the same deal (I have a 91) If that vac line goes up to the heater control I can chase the problem down easily as I have to R&I the radio to make some adjustments anyway.

This is for the pre 1990 experience guy... I have an 88. I pulled the ac Condensor off my Xj this summer since the ac didn't work anyway..now it's winter and my heater puts out 70 degree air at best..I have a thermometer in the vent. I have checked the vacum lines one by one and seem to have good vacum and no heater core leaks into the cab or anywhere else..what next is there something I have to plug cause the condensor is gone?

When was the last time the entire cooling system was flushed?If you only backflush every now and then,(I used to do this)the system will get deposits and evently affect the heater core as well as the radiator.
I backflush every year,usually in the fall, and put in a new t stat,replace any hoses that are bulging or cracked,and pour in new anti-freeze.
Doing this will keep the cooling system cleaner and in better operating condition.
Check all vacum lines from the canister behind the front bumper(passenger side) allthe way to the firewall,and any others in the engine compartment.
If any of these lines(small hard plastic) are broken,they can be spliced using
5/32 gasline hose (5/32 ID)ANY VACUM LEAK WILL AFFECT THE WHOLE VACUM SYSTEM,which can affect your gas milage also.
You gotta trust me on this,I fixed one vacum leak and now I have 4x4,fixed another,and I have to back the temp off on the heater adjustment.
T-stat will also affect the cooling system IF it is not letting the engine get up to the normal operating temp.

Like Churky says (good write up), might also check the cooling system for air. If the coolant level falls below the intake in the surge tank, it can cause heater problems also.
Most times, it´s vacume lines or a plugged up heater core. Have had the clip fall off of the flap (door actuator), heat sometimes, vent sometimes, kinda did it´s own thing.

My 89' had the "closed system"when I bought it.(used @ 4 yrs ago)I knew nothing about JEEPS,this being the 1st JEEP I have ever driven.
The cooling system to me looked like a plumbers nightmare.
Pressure bottle,various heater hoses,(11 or 12 hose clamps) running all over the engine compartment.
I had replaced all the hoses,the "pressure bottle",t stat,n even the oem style rad(no filler neck).The thing was constantly over heating no matter what I did
or which t stat I used.It was really starting to PMO big time.
I had read various posts about swapping out to the open system,so about the end of last August,I did the swap.Wish I'd done it sooner.It is easy and best of all it eleminates the pressure bottle.I now have 2 rad hoses,2 htr hosesgoing to the htr valve and 2 htr hoses going to the block.When I got through,I noticed that I had eleminated 12 htr hose clamps.When I finished,naturally I watched the temp guage more than I watched anything else.I have had no probs what so ever,but next summer will be the real trial.
But I don't think there will be any problems.If any body wants a list of what is needed,I would be able to e mail or PM a list of what is needed to do the swap.

http://www.cheapxj.com/ Has a good write up in the cheap tech column. Pix and everything. I think he uses a Pontiac sunbird bottle. Cheap from a boneyard.