Kzj 78 HVAC question

[Lomoski]

Hi friends!

Quick question. My heater only throws heat if it's all the way to the right, I move it one down and it's cold air. My heater blows the four different setting speeds. But only throws heat when it's hard right. Is this normal? If not, suggestions for rectifying? It's been this way since I have had it and have done multiple coolant flushes, burps, pressure tests etc. my coolant temp is normal and not overheating/under heating the motor.

Thanks!

Marc

 

[JuanJ]

Hello,

You might want to check the heater's radiator and the coolant valve. The former may need repair. The latter may need adjustment.

You might want to check the temperature lever's control cable. It may be loose.






Juan

EDIT: I forgot to mention that in old age, heater control cables can become either loose or stuck. They need tightening and lubrication; sometimes it is necessary to replace them.
The coolant valve can always be adjusted a little.
The procedures for cables and valve adjustment are in the FSM.
Heater radiators are as vulnerable as the main radiator to coolant quality.
Last but not least, it is a good chance to clean up the ventilation ducts.

 

[Bad Mojo]

I had a chance last night to drive the KZJ and I would say there is a gradient that is achievable with the heater control. That is with a brand new heater control valve controlled and a completely overhauled cooling system minus radiator.

You mentioned multiple coolant flushes. Right before the heater control valve was installed I did do a critic acid flush of the coolant system that did seem to help gain some smoothness in the operation of that old heater valve before it was replaced. I also compared the new and old valve and the new one does operate smoother. I am wondering if your full heat is really just partial heat and a valve that isn't opened all the way.

Let me know if you want pictures of the valve open and closed, so you can compare to yours.

 

[Lomoski]

I had a chance last night to drive the KZJ and I would say there is a gradient that is achievable with the heater control. That is with a brand new heater control valve controlled and a completely overhauled cooling system minus radiator.

You mentioned multiple coolant flushes. Right before the heater control valve was installed I did do a critic acid flush of the coolant system that did seem to help gain some smoothness in the operation of that old heater valve before it was replaced. I also compared the new and old valve and the new one does operate smoother. I am wondering if your full heat is really just partial heat and a valve that isn't opened all the way.

Let me know if you want pictures of the valve open and closed, so you can compare to yours.

I was going to pull the valve and run it through my ultra sonic cleaner. Thanks for confirming there should be a gradient. I'm barely getting hot air out and it's about to get to minus 33 centigrade here.

 

[Bad Mojo]

Are you getting any heat from the rear heater? I am wondering if you have a clogged heater core.

What inspired the coolant flushes? Was it the lack of heat like you are describing or something else?

 

[Lomoski]

Alright, just an update here in my journey. Pulled my valve and ultra sonic cleaned and lubed. Moves as expected and opens fully. I pulled my dash to replace the heater pipes and o rings as I had a drop of coolant leaking through my dash.

While taking my dash apart it became apparent very quickly about what was going on with my HVAC system. Firstly the foam which seals the various dampers in the HVAC system has turned to powder. Literally. You touch it and it turns to dust. So none of the dampers had been sealing. The fresh air/recirc damper wouldn't seal, the cold/hot damper was not sealing... Etc etc. So, I took all of the powdered foam off, ground off the adhesive with a brass wheel, painted the surfaces to stop surface rust and applied rubberized HVAC adhesive foam in 8mm thickness matching the old application...

But. PSA here, there appears to be no prefilter, other than the squirrel fan and HVAC evaporator. There was literally half an inch of debris and detritus on top of the evap coil which had completely killed airflow. It was amazing any air was getting through at all. So I separated the clam shell protecting the coil and cleaned it out with a foaming HVAC coil cleaner and flushed thoroughly with water. Couldn't get it perfectly clean but it's waaaay better. Put everything back together. With the new foam dampers and the clean coil and heater core this thing blows heat like a brand new vehicle. It's actually remarkable. It also explains why my fan died as it was trying to force air through a brick.


So hopefully this can help someone else. If you have some time, live in a cold or very hot climate where you need your HVAC system in top shape, I reccomend this "mod". You can easily do it in a day taking photos and putting respective screws in labelled baggies etc. You do have to get your HVAC system evacuated but that's not an issue. The difference is night and day and I can actually defrost my front window when it's minus 30c.

If anyone has any questions about the dash removal, I've done it a few times now on my kzj78 and can walk you through any questions pretty easily. I can reccomend parts from megazip required and what to look for. It's a good time to replace your speedo cable, dash lights, HVAC cables, get your ecu refreshed etc etc.


Enjoy the weekend!

 

[Lomoski]

 

[Bad Mojo]

Always nice to see an update on this kind of stuff. A good reminder that these trucks are getting up there in age and require special attention. I suspect this and redoing weatherstripping in ours will be in the semi-near future.