Sounds like the vacuum actuated valve that allows hot coolant to flow into the heater core when you select one of the heatng modes. The valve is probably common to all XJs/MJs, regardless of year/engine. I'm sure the dealer parts dept. would have them; the place of last resort./wwwthreads_images/icons/smile.gif

You could install a connector in the heater hose temporaily; you will just get heat all the time you run the fan./wwwthreads_images/icons/smile.gif

 

already did that.....runs fine collant cycles fine but I have no diff. in air function....dont get me wrong, thats fine with me but I agree with you, i should have hheat all the time...ac still works fine, of course the heat does as well? WTF?! weird...does the fluid const. run through the heater core when you turn the heat on or does it wait till the termostat kicks in? maybe only has coolant run throug it when the coolant gets hot? if thats the case then is leaving that valve off bad...just plug the vacume hose?
this is buggin the crap out of me...why is my heat not on all the time when I turn on the fan in any pos.?seems to me that even the ac should be blowing at least mild instead of cold?

Rick

 

Yeah, a tee at the local parts shop for full-time heater would do just fine temporarily.

Just because I don't care doesn't mean I don't understand!
'88 MJ SporTruck shortbed
Rebuilt 2.5L: 40 over rings, 10 on crank, 10 on bearings
nearing 400K

 

yeah I did that...
what I was saying is that everything still works fine...ac heat evrything,,, I ave no differance without the valve,. the air/ac still works fine...as does the heat. weird

Rick

 

Have you tried to get cool air from the dash vents in the vent mode??...just curious.

 

yup....works fine, doesnt make sence does it

Rick

 

That is really weird, oh well as long as it's working.

 

its called the heater control valve. had to do it on my friends the other week. not to hard to change.

-jon

I wish I had a 4.0...
oh wait, I DO have a 4.0!!!

 

ohh well....Im with you aj..
as long as it works


Rick

 

It might make a difference in the summertime; hot coolant bypassing the radiator.
I suppose that the control valve has to have some purpose./wwwthreads_images/icons/crazy.gif

 

Is this the part you are talking about?

If so, it is Factory Air part # 74774. Most Checker/Schucks/Kragen Auto Parts stores stores should have one.

IF IT'S NOT DIRTY, YOU'RE DOIN' IT WRONG

 

tazman you are the man! where did you find that?
anyway yeah...thats the one. I cut te valve off with a pipe cutter and just ran it as a " T " temp. , now just trying to figure out the negatives to doing this

Rick

 

Chieftan, the amount of heat is controlled by a door in the guts of your HVAC system. That's why you still have temp control. The Vacuum activated switch is either ON, or OFF, so there is no modulation. The door is hooked up to the temp lever by a cable. Most north american cars don't have that coolant valve at all, and always circulate coolant through the heater core. I guess the valve helps the engine warm up faster? Good for emmissions.

Just a mild 2" lift to fit the 31" BFG AT's

 

I guess what you're trying to say, nmaxs, is that the air flow across the heater coil is controlled by a damper; the damper most likely is opposed. Meaning that it allows air flow either over the A/C coil or the heater core, acording to what the temp setting is.

I think the valve is there to stop the flow of hot coolant when the heater is not in use in order not to bypass the radiator. Since there would be no heat transfer over the core, (no air flow) the pump would be recirulating "un cooled"
coolant back thru the engine.

 

That makes sense. The damper only directs air thru or around the heater core, and all air goes through the AC evaporator. One of the features of AC is that it takes moisture out of the air, which is a bonus for window defogging. If you switch the HVAC to DEF, the A/C will turn on, even if you have the temp lever at hottest. For that to work, all the air has to pass through the A/C evaporator to be dehumidified.

Just a mild 2" lift to fit the 31" BFG AT's

 

well......um, uh...what?
thats alot of greek to me guys..lol
so what are the cons/bad things that can happen by emilimnating the valve...its only 15 bucks...but nobody as it in stock which means a trip to jeep parts FT Knox( dealer) for a 30$ tab , if I dont need this thing...I wont buy it

Rick