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'88 Cherokee Heater

B

barece

NAXJA Forum User
Location
Springfield, OR
Hey, I've got an '88 Cherokee Limited, 4.0 w/ the AW4 and 242 transfer case. It has air conditioning. The problem I'm having is with the heater... when I turn the heat all the way up, and set it to any position(vent, defrost, floor, etc) it blows lukewarm, with occasional and extremely short(less than a second) pulses of stronger heat. I figured I was just imagining it, so I had a friend put his hand in front of the heater vent, and he confirmed it. Can anyone suggest some possible causes for me check? It's winter here in Oregon now, and I'm kind of hoping to stay warm, since I didn't notice this during the summer. :)
 
Most likely you have a vacuum leak causing the mixing valve to not actuate or the valve itself is bad. Open the hood and hold the little arm in the open position and see if it blows hot.
 
The valve is located in the heater hoses. Could also be a blend door problem.

heatervalvesmallru9dm0.jpg
 
couldn't hurt to back-flush the heater core.

I just busted a heater hose on the side of the road and when I went to remove the hose from the heater control valve it also broke. For a quick fix and since it is winter time, I removed the heater control valve. This keeps hot fluid running through the heater core all the time. I'll replace the valve in the spring.
 
I second flushing the heater core. If the core is even partially plugged up, you'll get no flow as the coolant just bypasses through the surge tank. You'll be amazed at how much crap you can get out of the heater core with a garden hose going back and forth between the fittings. I believe the default position for the valve without the vacum nline is to be open.
 
The mixing valve is a flap in the heater that mixes hot air with cold air it is not vacuum operated.
The vacuum controlled water valve is either full on or off, but it sounds like a vacuum problem, one usual spot is the line going to the vacuum reserve canister in the front bumper.
 
how are you guys flushing the core? I don't want to take the hoses off the core itself because they get so brittle, I guess I could take one leg off the stat housing and one off the tee and clamp the rest with vice grips
 
Another stupid question, but the engine's hot on my XJ and I don't want to have to wait for it to cool down to take the hoses off - on the heater control valve, which position is open and which is closed? When the little arm is retracted into the vacuum servo, or when the arm is pushed all the way out on the vacuum servo?
 
Ok - an update. I pulled both hoses off the heater core, ran a hose in it... nothing brown, only jewel green antifreeze, followed by perfectly clear and clean water, coming out both holes, depending on which hose I put it up against. So I figure the heater core itself isn't blocked up. So then I pulled the heater control valve off, since it was sufficiently cool, brought it upstairs, and confirmed that it's open sufficient to allow hot water through at a normal rate, by putting it under the faucet in the kitchen and running water through it. I also confirmed that the valve can be shut and that it does seal off the flow. However, from the position of the arm, it was fully open this entire time.

The heater core is getting hot water. So where do I check the flap in the dashboard that controls how much hot air is mixed with how much cold air? Or is there anything else I can check?
 
hopefully someone who's BTDT can post up on that flap because I'm not driving my XJ these days - it's -20 Celsius, and I only get true heat (and weak at that) on defrost. I'm sure my mixing flaps are buggered but it's just too damn cold to fix it out there without some pointers.....

anyone.....please? :)
 
I tried flushing my core following this write up: http://www.olypen.com/craigh/heater.htm

and no dice. The core I believe to be completely solid (when I pulled the tubes off, there was a solid wall of gunk inside each of the core inlets :shiver: ) Please don't tell me I have to replace the whole darn core... :badpc:
I've got an 88 also.
 
if your heater core is clean, the valve works, i am tempted to ask about your engine temp. if your tstat is stuck open, it is constantly cooling the engine and not letting it get to full operating temp.
 
What does your temp gauge say the temp is. My gauge is off i think cause my elec fan kicks on and it is only a needles width above the first mark.
 
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