97 TJ Heater Only Blowing Hot Air

[MarkHG]

Hi Folks, Our '97 TJ has a standard heating system (no AC) which has decided to only blow hot air, irrespective of whether or not the slider is set to hot or cold. In addition, the central air vents on the dash have stopped working completely. All and any advice sought as the potential causes, together with suggested fixes. If, as I have read, this is to dow with a leaking vacuum system, I'd appreciate any links/pointer as to how to repair/replace the relevant components as we are new to the TJ and don't yet know our way around it all. Thanks in advance.

 

[DuckNut]

If you have all heat and no blending of discharge, it is most likely a vacuum leak. You will need to track down the vacuum lines and inspect them. Since you will be chasing a crack, i would replace them all while looking for the leak. The age of it might cause you to break a hose while looking and maybe have to do it again in another year.

 

[Chris]

Yep, I think what you're dealign with is a vacuum leak indeed.

 

[MarkHG]

If you have all heat and no blending of discharge, it is most likely a vacuum leak. You will need to track down the vacuum lines and inspect them. Since you will be chasing a crack, i would replace them all while looking for the leak. The age of it might cause you to break a hose while looking and maybe have to do it again in another year.

Thanks for the reply. Confirms what I have been reading on-line but great to have this forum to get some real-world experience!

 

[MarkHG]

Issue has been identified. The return spring on the hot/cold slide is faulty. Only goes to hot, never returns to cold, hence the issue. Can't quite figure out how the return spring under the dashboard at the end of the cable works, but at least it's a minor mechanical issue with a cable return and nothing complex! If anyone knows how the return spring is supposed to look/work please do share.

 

[Rickyd]

Issue has been identified. The return spring on the hot/cold slide is faulty. Only goes to hot, never returns to cold, hence the issue. Can't quite figure out how the return spring under the dashboard at the end of the cable works, but at least it's a minor mechanical issue with a cable return and nothing complex! If anyone knows how the return spring is supposed to look/work please do share.

Have you pulled the HVAC controls off the dash to look at the back and trace routing and vacuum lines?

I don't recall there being a return spring on the blend door when I did a heater core on my 97. Just the cables. I could be wrong though.

A good way to test the lack of routing the air to different outlets is with a hand held mityvac vacuum pump. When you suction the different lines you can verify operation and that they don't leak. Watch for broken actuator arms that get driven by the vacuum pods.

 

[jonny jeep]

The cable pushes and pulls the lever. The cables have been known to kink which can stop heat selection working properly.

There is a spring that rests on a cam on the lever, but I think it's to hold the lever in position when a mid heat level is selected.

 

[MarkHG]

The cable pushes and pulls the lever. The cables have been known to kink which can stop heat selection working properly.

There is a spring that rests on a cam on the lever, but I think it's to hold the lever in position when a mid heat level is selected.

Thank you Jonny. You are completely right, the issue is the cable itself, it refuses to 'return' most likely due to a kink - I will take it out and check - but I can manually return it by pushing the cable end under the dash - effectively putting the dial back to cold.

 

[MarkHG]

Have you pulled the HVAC controls off the dash to look at the back and trace routing and vacuum lines?

I don't recall there being a return spring on the blend door when I did a heater core on my 97. Just the cables. I could be wrong though.

A good way to test the lack of routing the air to different outlets is with a hand held mityvac vacuum pump. When you suction the different lines you can verify operation and that they don't leak. Watch for broken actuator arms that get driven by the vacuum pods.

Hi Ricky, You're right, it's not a return spring it's just a tensioner. The issue is the cable, it is kinked or snagged and won't 'return' only operate one way.

 

[Rickyd]

Hi Ricky, You're right, it's not a return spring it's just a tensioner. The issue is the cable, it is kinked or snagged and won't 'return' only operate one way.

Perhaps you can bend the wire straight again and adjust it? I had to do that on a 98.i also added dry graphite powder to get the cable to move more freely. Dry graphite doesn't gunk up the way liquid lubricants do

 

[MarkHG]

Perhaps you can bend the wire straight again and adjust it? I had to do that on a 98.i also added dry graphite powder to get the cable to move more freely. Dry graphite doesn't gunk up the way liquid lubricants do

Thanks - I am going to try just that to start with (seeing cables on-line for $100+ makes me decide I'll try the repair first...). Thanks for the note about dry graphite lubricant!