[MoparMan1990]

'00 larado 4.0 select-a-trac

Was on my way home had the heat on full blast I noticed that the air flow went from front vents to defrost and back all within maybe 3-4 seconds it's never done that before and it seams fine now but it was only a five minute drive also it's not dual climate any thoughts I hope it's not the blend doors

[the88thpianoman]

It's a lack of vacuum on the AC/cruise control vacuum line. Inspect or replace the line, and add a check valve.

The check valve didn't work for me, so I'm looking at adding an extra vacuum reservoir on that line.

[chrism1367]

If you dont have dual climate then you dont have blend doors...

[MoparMan1990]

Where can I find the vacuum lines and Chris I did not know that thanks for the info I feel stupid lol

[HVACNY]

Originally Posted by chrism1367

If you dont have dual climate then you dont have blend doors...

Not correct,he just doesnt have dual climate to have seperate temps on each side of his interior.He can still control whether he has hot or cold or warm air with his temperature knob.And that means theres a door to blend the air,and they can fail.

[MoparMan1990]

Originally Posted by HVACNY

Not correct,he just doesnt have dual climate to have seperate temps on each side of his interior.He can still control whether he has hot or cold or warm air with his temperature knob.And that means theres a door to blend the air,and they can fail.

Is this a common problem For my type of hvac system

[imaguy3]

Originally Posted by MoparMan1990

'00 larado 4.0 select-a-trac

Was on my way home had the heat on full blast I noticed that the air flow went from front vents to defrost and back all within maybe 3-4 seconds it's never done that before and it seams fine now but it was only a five minute drive also it's not dual climate any thoughts I hope it's not the blend doors

Originally Posted by HVACNY

Not correct,he just doesnt have dual climate to have seperate temps on each side of his interior.He can still control whether he has hot or cold or warm air with his temperature knob.And that means theres a door to blend the air,and they can fail.

But we know it's not the blend door b/c he's not complaining about temp. problems... and I haven't read a single case on here of someone without dual zone having a blend door break... so it's a pointless argument.

Did the change take place while you were accelerating? If so read this..

http://wjjeeps.com/climate.htm

Heater A/C system changing to defrost mode when accelerating - 1999-2000 models (see TSB # 242499)

http://wjjeeps.com/tsb/tsb_wj_242499.pdf

[MoparMan1990]

I believe it was when accelerating I live off a state highway so I have to get on it to make a left ill have to look for these vacuum lines tomorrow

[BriansCJ]

Check for a vacuum leak like posted above.

[BWYoung85]

Sounds like an intermittent vacuum leak, I replaced the vacuum line under my battery tray because it was cracked. Once completed I got my AC Controls and Cruise Control back.

[Cirruslydakota]

Yep, typical vacuum line problem, easy fix.

[chrism1367]

Originally Posted by HVACNY

Not correct,he just doesnt have dual climate to have seperate temps on each side of his interior.He can still control whether he has hot or cold or warm air with his temperature knob.And that means theres a door to blend the air,and they can fail.

Sorry, meant he doesnt have the blend door problem

[MoparMan1990]

This is the only vacuum line I can find and it looks fine am I just not looking in right place and FYI my cruise control is working

[chrism1367]

Check the ones going to the intake manifold and that whole area. I had one pop off once.

[imaguy3]

read the TSB... it talks about placing a check valve in the vacuum line, your lines may be fine, it mya just need that valve