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heat issues

j-nut

NAXJA Forum User
Location
new hampshire
I've got a 95 xj with a 4.0. When I bought it the heat was very weak. Lately there has been no heat. Today while doing the water pump I disconnected the vaccum line off the accuator that is on the heater hose. With the vaccum line disconnected the heat works perfectly fine. Does anybody have any suggestions on what I should look for?
 
is it not blowing, or not getting hot? the vaccum system controls a series of flaps that open and close to direct the air, and open and close the heater valve under the hood. the heater valve controls whether or not the coolant flows through the heater core.
 
which is strange all the heat system is mechanical. and absence of vac to any climate control. will default to heat on and all vents to defrost. but how can vacuum get stuck on. very strange?
 
I thought it was strange too. It is blowing fine and I can control the vents. The valve under the hood is getting constant vaccum, which is not allowing coolant to flow to the heater core. Right now I have the vaccum line to the valve disconnected and the heat is working perfectly. But as soon as I connect the line, it only blows cold air.
 
The heater control valve default is closed with vacuum applied. When the heat is turned on at varying degrees the vacuum is limited in relation to the desired amount of heat to supply varying degrees of coolant through the core. If you have constant vacuum at the vacuum supply then you most likely have a faulty heater control valve (engine compartment).

Check to see if your heater control valve is working by (with motor running and heater controls off) disconnecting it and look to see if the small lever on the other side move in/out. Then do the same thing with the motor running and the heater controls on. If nothing moves, it's the valve. If it moves in and out as you adjust the heater temp controls then it's OK. Thus ends my experience.

You can also re-route (replace) your hoses to run completely valve-free as the later models do. It's always a good idea to flush out your core by disconnecting the hoses and shooting a garden hose through there, alternating top & bottom until the water runs nice and clear.

If it's just the valve you can get one at AutoZone for about $25.
 
Not to hi-jack but, I actually just have relatively weak heat. Curious, what's the deal with the not so typical hoses? It looks liek they have some kind of crimp on them? Kinda similar to A/C lines? I'm talking about the ones on the core itself.

89 Cherokee
 
The valve is working properly. The vaccum is not changing with the heater controls.

Pioneer- Mine started off with weak heat and then all of a sudden I had nothing.

I'm leaning towards just elminating the valve if I can't figure out where the problem lays.
 
I think the problem is the control head, since it is what sends vacuum or vents it off to the valve. I checked mine today and it has no vacuum with the lever all the way to hot, and vacuum with it all the way to cold.

Curious. 97+ don't have the overflow bottle there? My 89 has a two tees for the overflow integral with the valve.
 
Overflow for 97+ is in the same spot as it has been since 1992.

Flow to the heatercore is 24/7 with 97+ without the heater valve.

x2 on the control head, but before he replaces that....can you verify that it is a tan vacuum line running through the firewall to the heater valve?
 
yea, it is the tan vaccum line running to the valve. I have access to a control head for free, so I'll give it a shot. Whenever I'm able to find the time that is.
 
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