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No Heat, Blend Door replacement?

K

kadetklapp

NAXJA Forum User
Location
West Central Indiana
I've flushed my cooling system twice and removed the heater hoses and flushed the heater core myself, and it has flow.

I have NO heat. Engine is at proper operating temp. Upper hose is hot to the touch when engine is at temp. However upper hose always seems to be dry.

My fan resistor pack went out and all I have is the highest fan setting. No heat whatsoever when cranked all the way to the right. I'm assuming it's the "blend doors" everyone keeps talking about.

I need to know the procedure for replacing these, and I need it quick. It's getting cold. Haynes manual does not cover it, and all the threads I find are for WJs and ZJs.
 
Do you get any airflow from the vents or floor. If not, and only from defroster vents, could be a vacuum issue. The bottom slider, for temp, is a cable, and you should feel resistance as you slide it back and forth. Do you have A/C? Is the shut-off valve working properly? I believe that they default open, unless the slider is all the way left, then it shuts off flow to the core. Make sure it's working OK. Then you can move on to see if the core is not clogged.
 
I should have stated, it's a 99 XJ, so it has the knob setup controls, and it does not have a heater valve. I have air flow out of all vents. It's just either cold air with AC, or outside air.
 
Ok, I tore into it friday night and confirmed two things-

One, the stepper motor used to control the blend doors functions fine.

Two, the resistor pack for the fan control is shot, and I located it.

Other than that I still have NO heat. The cooling system is full, and my Jeep has a consistant operating temp of 197*F per my ScangageII.

Its starting to get chilly here and I need some assistance asap.
 
What do you mean when you say the hose is "dry"? Both hoses from the core should be hot.
 
Just ran it hard down the road and back and I've come to the conclusion it's the doors. I've got hot fluid in the upper hose now, I was simply too low when I was checking it a few weeks ago. I gave it a good thorough flush and I have nice green coolant thruout the system, and it's high pressure at the cap. The heater hoses are both VERY hot and feel firm to the squeeze.
Inside the truck I again confirmed that the door motor was working and then beat on the box with a flashlight to see if I could get the doors to move some. No dice. Still have no heat. I get a little inkling out of the center floor vents, but nothing on the sides and NOTHING up top. Just cool outside air.
I really do not want to go through with this. This is seriously beyond my expertise. There is a lot of crap to screw up during the process of removing the entire damn dash. I don't have the $900 to pay a shop to do this either. What a drag, dood...
 
OK, step one, disconnect your heater hoses, go buy a new pair cause you are going to take them off with a razor knife.
Step one, remove the factory clamps on the heater hoses on the firewall.
Take the razor knife and slice the hose LENGTHWISE, then peel it off, DO NOT pull it off or twist it, if you break one of the bungs you will need a new heater core.
Once the hoses are off, take you garden hose and shoot it into one of the heater hose bungs, see what comes out the other side, if it comes out all black and chunky keep it up, reverse the hose to the other hole and repeat, keep switching back and forth.
Once it comes out clean and runs steady replace the hoses with the new ones.
DO NOT stick that house water hose on there and seal it to get more pressure, most houses work on 30-60PSI, that cooling system is rated for 16 lbs, you will blow the heater core apart.
Next, after it is all back together pull your center bezel on the dash board, remove the heater/hvac control, the blend cold to hot dial is controlled using a cable, yes a cable, make sure that cable is still connected on BOTH ends.
one of those should fix your problem.
 
OK, step one, disconnect your heater hoses, go buy a new pair cause you are going to take them off with a razor knife.
Step one, remove the factory clamps on the heater hoses on the firewall.
Take the razor knife and slice the hose LENGTHWISE, then peel it off, DO NOT pull it off or twist it, if you break one of the bungs you will need a new heater core.
Once the hoses are off, take you garden hose and shoot it into one of the heater hose bungs, see what comes out the other side, if it comes out all black and chunky keep it up, reverse the hose to the other hole and repeat, keep switching back and forth.
Once it comes out clean and runs steady replace the hoses with the new ones.
DO NOT stick that house water hose on there and seal it to get more pressure, most houses work on 30-60PSI, that cooling system is rated for 16 lbs, you will blow the heater core apart.
Next, after it is all back together pull your center bezel on the dash board, remove the heater/hvac control, the blend cold to hot dial is controlled using a cable, yes a cable, make sure that cable is still connected on BOTH ends.
one of those should fix your problem.
Click to expand...

I've already flushed the heater core three times and the entire system twice. Nasty black crud flowed out and then was crystal clear. The motor controlling the blend door is electric and controlled by the dial and I've already confirmed it's function.
 
kadetklapp said:
I've already flushed the heater core three times and the entire system twice. Nasty black crud flowed out and then was crystal clear. The motor controlling the blend door is electric and controlled by the dial and I've already confirmed it's function.
Click to expand...

Per Factory service Manual, page 24-37 figure 42 and page 24-38 figure 43, Temperature control cable, it's held in place similar to a cable on a hand brake on a bike or MC, they can slip out if the retainer flag slips off from vibration.
The cable actually operates the blend door, not a vac motor. That also has a push nut on it, if it comes off the lug on the end of the cable it will come off. The vac motors only operated the flappers to decide where the air comes out of, nothing else.
 
Per Factory service Manual, page 24-37 figure 42 and page 24-38 figure 43, Temperature control cable, it's held in place similar to a cable on a hand brake on a bike or MC, they can slip out if the retainer flag slips off from vibration.
The cable actually operates the blend door, not a vac motor. That also has a push nut on it, if it comes off the lug on the end of the cable it will come off. The vac motors only operated the flappers to decide where the air comes out of, nothing else.
Click to expand...

Are you looking at an FSM for a 99? Because that's what the blend doors are controlled by, an electric stepper motor. There is no cable that I see coming from the HVAC control unit for temperature. The electric motor has a plastic axle that goes inside the bottom of the heater box. This is just to the right of the trans hump under the dash. You can see it without removing anything. The motor turns the axle and rotates the door.
 
Last edited:
kadetklapp said:
Are you looking at an FSM for a 99? Because that's what the blend doors are controlled by, an electric stepper motor. There is no cable that I see coming from the HVAC control unit for temperature. The electric motor has a plastic axle that goes inside the bottom of the heater box. This is just to the right of the trans hump under the dash. You can see it without removing anything. The motor turns the axle and rotates the door.
Click to expand...

Oh thats frigging wonderful, substitute an electric motor for a .20 cent cable. Wonder how they slipped that past the accountants.
I'm looking at my 98's FSM. So far I have found no differences between the 98 and 99's, this is the first one I've come across, I always pictured the dividing line being when they went to multi coils on plugs.
I'll tell you what did happen on one of my TJ's, the flapper door which is vac actuated for floor/dash/defroster doors broke, it was the plastic tab that went into the flapper itself. I fixed it with a long self tapping screw by screwing the tab into the shaft which already had a hole in it and now the defrosters work fine. If you have water flowing thru the core then the only thing it could be would be the blender. With a stepper motor involved thats about all I can help you with, sorry.
 
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