HVAC controls bleeding down?
 

1990 4.0l

When I shut the Jeep off with the heat running on floor (verified it is blowing on floor) it sounds like a hissing sound from the passenger foot well like a blow off valve. Not loud, just the diminishing air escaping sound. Clear as mud? Is this normal or should I look for a leaking vacuum component?

With the engine off I have pulled a vacuum on the line going into the vacuum ball and it held, no leaks.

Under dash pass side there a vacuum diaphragm .

Have you tried it with the HVAC controls off before hutting down?

Yes. No bleed-down noise with controls off at shut down.

Turn the controls OFF before shut down as a regular operation.

Remove the cover off the blower resistor (see pic) so you can see the recirc air door actuator. See post #2.

With the engine running and the controls to heat, shut down the engine and see/hear if the recirc air door actuator is your problem.

Do the same with the controls OFF.


Attachment 305587
.