Strange noise when turning heat off

HI All,

I have had three Cherokee's in my life, and '87 & '88, and the current one, a '91.

None of them have ever made any noises when shutting off the heat until this one. It sounds like something cycles, like an electrically driven valve closing up in the front of the engine bay or something. Anyone know anything about this?

Thank you.

i think there is a flap in the hvac that closes when the controls are set to off. my 90 does it only its very squeaky.

Any chance theres a way to get in there and grease it?

i have not taken the dash apart yet to even see the hvac box. i will be this spring in my 88.

My 88 does it. When you slide the control to the left you open the vac port and vent the lines. The affected door then returns to it's No Vacuum position. I notice this when I shut the engine off first, then slide the controls to off.

When my car sits for a few days, the vacuum bleeds off. When I start, I can hear the doors move.

I think this affects the recirc and defrost doors.