Heat adjustment help! 94 FZJ80 (1 Viewer)

[steezedae]

Having some issues trying to get my heat to adjust from cold to hot and vice versa. If I pop the hood, i can open and close the valve manually to obtain heat or cold, so in the summer I close it and the winter I open it, so I know the valve isn't the problem. If i disconnect that cable at both ends, I can move it, so I figure the cable is fine. But when I slide the temp on my climate control unit, that cable doesn't move. Not sure why.

Any ideas?

Thanks!

 

[steezedae]

Also, I made sure the climate control unit is set to Manual and not auto when i took it out and tested with another unit. Didn't fix my problem..

 

[steezedae]

any ideas?

 

[JoeCova]

I am diagnosing mine this winter as well but if I recall there is a servo in the back that essentially moves the cable and that servo may not be working. I'll see if I can find the old thread I was referencing.

 

[SpenserAK]

Turn the key to "on" & cycle the temp slider from full cold to full hot in one move - listen for the servo motor in the dash making any noise. If quiet, I agree it's likely you have an issue with the motor.

Another thing to consider is the potentiometer that adjusts temp, which is on the back of the HVAC box. Mine is wonky... it keeps the valve closed until I get to full hot (85°+) and then fully opens it, so I effectively have a heat on or off function, no blending. I'm no electrical expert by any means, but I'd think it's possible your potentiometer isn't working, so it's not actuating the motor at any point. If that did happen to be your issue, there's a thread detailing how to go about fixing it by re-soldering the 3 joints on the back.

Erractic Heater Temp Control Fix

My heater was possessed. But after a simple exorcism, all is well. I've had this problem with my heater on my '94 FZJ80 for some time. I would select a temperature with the slider and randomly the heater would go to full heat. I could jiggle the temperature slider and it would return to...

forum.ih8mud.com

 

[steezedae]

Okay I'll check tomorrow and see if I can hear the servo motor working

 

[steezedae]

Turn the key to "on" & cycle the temp slider from full cold to full hot in one move - listen for the servo motor in the dash making any noise. If quiet, I agree it's likely you have an issue with the motor.

Another thing to consider is the potentiometer that adjusts temp, which is on the back of the HVAC box. Mine is wonky... it keeps the valve closed until I get to full hot (85°+) and then fully opens it, so I effectively have a heat on or off function, no blending. I'm no electrical expert by any means, but I'd think it's possible your potentiometer isn't working, so it's not actuating the motor at any point. If that did happen to be your issue, there's a thread detailing how to go about fixing it by re-soldering the 3 joints on the back.

Erractic Heater Temp Control Fix

My heater was possessed. But after a simple exorcism, all is well. I've had this problem with my heater on my '94 FZJ80 for some time. I would select a temperature with the slider and randomly the heater would go to full heat. I could jiggle the temperature slider and it would return to...

forum.ih8mud.com

Can't hear any sound when sliding the temp adjustment. Also tried swapping in another climate control I had and that didn't do anything. Is it time to pull the dash and get to that servo? Or can I remove it without fully taking out the dash?

 

[SpenserAK]

For the sake of not leaving you hanging - truthfully, I don't know. I've never had to work on the motor, and have only taken apart the hvac area and instrument cluster, but not the whole dash. Hopefully someone can chime in.

Found this thread (which I had posted in for help). There may be bits of helpful info.

Heater control valve Servo Motor

New to the family 1993 fzj80. I am in the process of diagnosing why I have no front heat. I have a solid temp reading on the dash. With the cable disconnected at the firewall the valve feels to move freely. When I removed the radio and disconnected the cable at the servo motor the cable moves...

forum.ih8mud.com

Here are a couple other threads that may have clues to aid you, but you'll have to do your own nitpicking through them, for your case

Servo motor

first post to mud. Been lurking for a few months but now I’m at a spot where I need some help. Just did a cooling system overhaul. Changed all hoses, changed my heater control valve, drive belts, fan clutch, PHH, full coolant flush including heater coils. Still I do not have hot air coming...

forum.ih8mud.com

1996 fzj80 dash vents not working properly.

i am having a strange issue with my truck. I know a servo motor has gone out but I cannot for the life of me find which one. My ac and heat work great but it only comes out of the outside dash vents closest to the door. I can hear any door moving at all when I switch from feet to defrost or the...

forum.ih8mud.com

Much may be unrelated, but some of the best solutions I've found have come from the culmination of scraps pulled from many sources.

If you are doing searches and don't already know, google is much better than the forum's built-in search

Best of luck!

 

[steezedae]

Thanks for the reply, I think I've seen a couple of those threads. I'll read up on them some more. My buddy has a 94 and I think I'm gonna grab a couple parts off it and do some tests with the AC amplifier and check some relays. I'll report back what I find

 

[12bit]

Turn the key to "on" & cycle the temp slider from full cold to full hot in one move - listen for the servo motor in the dash making any noise. If quiet, I agree it's likely you have an issue with the motor.

Another thing to consider is the potentiometer that adjusts temp, which is on the back of the HVAC box. Mine is wonky... it keeps the valve closed until I get to full hot (85°+) and then fully opens it, so I effectively have a heat on or off function, no blending. I'm no electrical expert by any means, but I'd think it's possible your potentiometer isn't working, so it's not actuating the motor at any point. If that did happen to be your issue, there's a thread detailing how to go about fixing it by re-soldering the 3 joints on the back.

Erractic Heater Temp Control Fix

My heater was possessed. But after a simple exorcism, all is well. I've had this problem with my heater on my '94 FZJ80 for some time. I would select a temperature with the slider and randomly the heater would go to full heat. I could jiggle the temperature slider and it would return to...

forum.ih8mud.com

I had the same issue on a 94. I reflowed the solder on my climate control as mentioned in that thread and it completely fixed my problem.

 

[steezedae]

I'll check them again but I ruled them out because I tested another unit I had and it didn't fix the issue. There is a chance the potentiometer is broken on both but i doubt it. But who knows with parts this old.

 

[Malleus]

Can't hear any sound when sliding the temp adjustment. Also tried swapping in another climate control I had and that didn't do anything. Is it time to pull the dash and get to that servo? Or can I remove it without fully taking out the dash?

Yes, it's possible, but you'll hate yourself if you try it that way. It's not that much work to remove the instrument panel, it's just time consuming and there are a lot of different parts.

I strongly suggest downloading the FSM, if you haven't already, and printing the section on removal before starting work. Don't forget the first pages with the parts diagrams and the page with the fasteners on it. I have a storage box with separate bins just for this job. It has the fastener page under the lid.

 

[steezedae]

soldered the points on the back of my climate control just to double check and nothing changed. Found a servo amplifier at a junkyard that I'm going to try and swap in soon and see if it fixes my problem

 

[steezedae]

update, still no heat adjustment, and my cable still doesnt move when i slide the climate control. Swapped in a couple ac amplifiers and climate units, still nothing.