Vaccum and air conditioning issues

[Akula69]

As posted previously, my son and I have completely overhauled the engine bay harness for the 89 MJ due to the PO having put a WJ A/C system in it and really messing up the wiring under the relays. We used a C4C XJ harness form the same year...it was mostly plug and play after we cleaned it and fixed a few abraded spots.

 

Before that we went through the entire A/C housing in the dash...replacing the foam insulation and the evaporator and heater cores. We also replaced the condensor and the receiver/dryer assembly. All new O rings and fresh compressor...thought we were good to go.

 

The harness went in cleanly, and the truck started right up. After pulling a vaccum on the A/C system and then charging it with freon I noticed that no matter where the selector switch was set on the dash, the air just came out of the defrost.

 

Now, before you say 'vaccum problem' let me say that we replaced the 'blimp' and the lines with a set that came from an XJ that still had a vaccum on it when I disconnected them! With the engine running I can disconnect the cap from the cruise control vaccum line and it has a strong vaccum. When I disconnect the vaccum line for the A/C (black line that goes into the A/C housing) it also has a strong vaccum.

 

 

The only other thing that I note is when you move the selector lever there is no 'hiss' that you would normally hear, and when you select heat the air gets really hot but the heater control valve in the engine compartment does not cycle (seemingly no vaccum).

 

Does anyone have any other ideas as to what can be checked? We have gone through all the electrical troubleshooting, and the system performs as it's supposed to (A/C blows cold, heater blows hot, etc.)

 

Thanks

[mfpdm]

Check the vacuum valve thingy(sorry, don't know what it's called) under the dash on the drivers side of the air box. That moves the flapper thingy inside of the box to direct where the air should go. They may be bad or just bound up. When you had the box apart you may have mis-aligned it or put it on wrong by mistake. Un-hook the arm and see if you can manually shift the air flow.

 

:cheers:

[Akula69]

We checked the actuators with direct hookup of a vaccum pump after re-assembly (but before installation) because I was worried about the clearance of the new foam insulation in the case by the air doors.

 

I'm almost starting to believe there might be a blockage in the vaccum hoses on the case itself, but don't know of a way to check them.

[dasbulliwagen]

Check to see if you have vac coming to the HVAC control head. There is a connector there that send vac to where its needed to change the blend doors, you may have a bad controller or it may not be hooked up properly. Let us know what you find! Good luck!

[64 Cheyenne]

Did you make sure you put vacuum to the correct port on the "blimp", it only goes one way, one side has a one way orifice on it.

[Akula69]

Did you make sure you put vacuum to the correct port on the "blimp", it only goes one way, one side has a one way orifice on it.

 

 

Yeah, I thought about that and checked to be sure the black line coming from the HVAC was hooked to the vaccum side.

 

I'm gonna unhook the harness from the back of the controls and see if there is vaccum there...if not its probably pinched in the dash somewhere, or if it does have it I'll have to swap out controls.

 

I did find a used vaccum harness on fleabay for 23.00 (Highway Robbery, I know :oops: ) and picked it up as well.

 

Thanks

[64 Cheyenne]

Maybe use a mityvac, see if the heater doors are working properly.