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Great Wise and All Knowing Jeep Wizards

C

CrawlingCritter

NAXJA Forum User
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I've been searching posts here and on other forums about having warm only heat in an XJ. I have a '90 Laredo and I've backflushed the coolant system, changed the thermostat (190 F), removed the heater control valve and replaced it with a piping assembly I rigged up from parts at the local hardware. So far nothing has helped. :bawl:

I'm left with:
1. maybe a failing water pump?
2. maybe the blend door needs adjustment?
3. maybe I need to move to Hawaii?

Does anyone know how to get to the blend door and how to adjust it? Anybody have/had similar problem and know how to fix said problem?

I hate this cold weather....:smsoap:




:flame: --that feels better
 
No mice nests in the heater core box? Not a bunch of crap on the heater core? Fuss, leaves, etc. Just wonder, I have seen it before Your right about the door. Check to be sure the door is moving all the way.
 
are the two hoses to and from the heater core getting hotter than "warm" ??

It is still possible that the heater core is partially plugged and only allowing a small amount of coolant to flow through it. If neither hose to it are getting as hot as the rest of the cooling system, I'd say blockage. If the input is roughly as hot as the cooling system and the outlet is noticeably cooler, I'd look at a blend door problem.
 
I would check my vacuum lines going to the canister behind the front bumper. R/Side IIRC. Thats what helps the blend door open. Sounds to me like your stuck on cold.
 
mcnamaag said:
I would check my vacuum lines going to the canister behind the front bumper. R/Side IIRC. Thats what helps the blend door open. Sounds to me like your stuck on cold.
Click to expand...

worth a look as well-- but doesn't it usually default to defrost without vacuum as well?
 
Sounds like your heater core is clogged. Very common. Doesnt get un-clogged during a flush either. Unplug the hoses from the heater core, and flush starting with the bottom spout from the core. I suggest hooking up a extra hose to the core, and attach the other end to the garden hose. Wait till the water is clear, and then move to the other spout and do the same thing. Alternate like this a few times, and then hook the two heater hoses back up to the core.
Enjoy heat!
Dont try to use the garden hose directly to the core as it will spray out the sides into the "foam" gasket on the firewall soaking it, and making your passenger side floor very wet. Also the amount of pressure obtained hooking it up directly could also push a hole in the core causing a huge huge headache.
Its likely to get clogged again, or even worse spring a leak since whats clogging it is corrosive. It may not, not very many complain of it leaking after a flush, just want you to be aware of what could happen.

Hope that helps.
 
Shorty said:
worth a look as well-- but doesn't it usually default to defrost without vacuum as well?
Click to expand...
I think you are right about the defrost being the at rest position if no vacuum is sent to the blend door.
The checking of the hoses will determine if the hot water/coolant is circulating through the heater core as it should. It will also tell if a clog exists in the form of gunk in the core or if the heater valve is opening fully.
 
Shorty said:
worth a look as well-- but doesn't it usually default to defrost without vacuum as well?
Click to expand...
Likely a partially plugged heater core, the heater core is kind of marginal anyway, anything less than optimum flow will degrade the heat.
On the non A/C models the outside air blend door, wire control, can pop off of the arm. The faster you drive the more cold air it lets into the blend.
 
mcnamaag said:
I would check my vacuum lines going to the canister behind the front bumper. R/Side IIRC. Thats what helps the blend door open. Sounds to me like your stuck on cold.
Click to expand...

I thought the blend door on a 90 is mechanical? Have a look under the passenger side of the dash near the tranny tunnel and you should see the little crank arm and the cable attached. The heater control valve (not an issue here) closes off the flow with vacumn.
 
I flushed the heater core directly, then a few days later flushed the whole system. I don't think this Jeep was maintained very well because I flushed it twice this past summer and got a lot of brown crap out of the system. I also changed the trans fluid this last time too (third time since I bought the jeep) and its starting to look better (first time it looked like cooked motor oil). The 4.0 and AW4 must be tough cookies.

Is there some way to remove the glove box and cut a hole in the heater box? This would allow an inspection and vacuuming out the box. I could then silicon everything back up???
 
My bad I was under the impression he only had defrost. Got it confused with another thread.
 
lawsoncl said:
I thought the blend door on a 90 is mechanical? Have a look under the passenger side of the dash near the tranny tunnel and you should see the little crank arm and the cable attached. The heater control valve (not an issue here) closes off the flow with vacumn.
Click to expand...

:flame: HEAT AT LAST! A close look at the little crank that sticks down out of the plastic duct that controls the blend door and I discovered my problem. The factory clip that holds the aircraft cable to this rod was slipping I set the heat control all the way to 'hot' and pulled the blend door rod so that it was against the little plastic stop sticking down from the air plenum. I pulled off the old factory clip with pliers and replaced it with a 1/4" wire rope clamp which could be tightened down so the aircraft cable wouldn't slip as it pushed the blend door rod back and forth. Works good so far...:party:
 
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