So I am kind of new to jeeps but have been around cars all my life. So here is my problem. I have a 89 XJ and the entire cooling system is new except the heater core. I am getting warm air when it sits and idles. When I get it on the highway or around town it will go to ice cold. Now the really crazy part is the jeep will never over heat. It barley reaches 210. I took the fan and fan clutch off and run just the electric fan off a switch but never have to turn it on. Also when I am driving if I have the vent on heat which is the floor it will switch to defrost. Any help or suggestions I can try I would greatly appreciate it.

 

Welcome to the forum. Your 89 will have a Renix specialist here soon.
In the meantime, what I understand from (at least non-renix) " going to defrost setting" (for instance if you accelerate) , is that this has to do with vacuum loss. As a default, it will go to the defrost setting.

 

Correct advice from Down Under.

Here is a vacuum diagram of the vacuum system below.

As for the heating issue, begin by replacing the thermostat with a 52028186 from the dealer and flushing your heater core.

 

Here's a functional diagram of the AC/Heater system.


As pointed out, a vacuum leak may be causing your problem, including loss of vacuum to the water valve in the engine bay.













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Thanks for the info. Ill have to check those out because I don't think I saw the vacuum canister under there. I have flushed the system twice already and change the thermostat twice. Ill go get one from the dealer and try that one.

 

Thanks for the diagrams. But as far as the water valve it is no longer there. So I know that's not one of the problems.

 

You may have a Vacuum Reservoir that looks like this (if you have cruise control).

 

Look for something like this:

 

So I defiantly do not have that in my bumper. But will that not being there cause the heat issue or is it more just for vent control?

 

Is involved with a few things...you will need to go get one if you truely have none..

 

Well I got the vacuum reservoir and it does help hold the position on the vents but I still have barley warm air.

 

Check security and operation of the Blend Door cable on the bottom of the HVAC Unit.


You should be able to move the bottom slider on the AC/Heater control back and forth and see the Blend Door bell crank arm move from side to side.


See pic.


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