Need a new heater core, presumably.

[ChickNorris]

Apologies for the resurrection of the thread but there is a little issue, my air vents are stuck on the defrost vents & air conditioning my windshield now. Anyone have a guess as to if it can be solved without having to pull the dash again? I never did replace the cover & it wont survive another attempt.

Fwiw I replaced the tubing that was in poor shape that goes from the engine compartment, to the port in the firewall that I believe controls the majobber that directs the air flow. Didn't remedy.

Control switch on the console maybe or ?

Appreciate any suggestions.

[ray1970]

Probably a vacuum leak somewhere.

What kind of vehicle? Ford?

[buffalobo]

Dodge 1500.

What Ray said.

We had similar issue with Mrs bo 1500 and Durango. Both would still change venting but had to lift off or apply throttle to vary/change vacuum "manually" and get it to actuate.

[Irving]

Hmmm, I'm having the same problem with the actuator in my Trooper. Interested in the fix.

[buffalobo]

We got rid of both vehicles before it stopped actuating completely, no idea what the fix was.

[ChickNorris]

It happened just a few days after the heater core was installed, ive just been living with it. Would like to correct it now but I really dont want to pull the entire dash/console off the truck frame again. Was hoping there was a fix someone had already tried & was easier.

99 1500 Laramie regular cab 5.9l

[DenverGP]

Many cars use vacuum to move the blend doors to determine where the air flows.

The vacuum comes from the engine, but only at certain throttle position/RPM (when the throttle is open, little or no vacuum is present).

So cars will have a small plastic vacuum "ball" hidden somewhere inside, with a checkvalve. That ball will provide enough vacuum to keep the blend doors working.

But it's common for the ball to crack, or rub against something and develop a hole. Or check-valve can also fail. In all these cases, the doors will only move while throttle is closed, usually with higher rpm as well (so a quick blip of the throttle to get rpm up, and release throttle quick, resulting in higher RPM with throttle closed)

For ChickNorris' issue, since it happened immediately after replacing a heater core, I'd bet a vac line or electrical connector got disconnected or knocked loose.

[ChickNorris]

So, removal, futzing & a new dash cover then?

[buffalobo]

Many cars use vacuum to move the blend doors to determine where the air flows.

The vacuum comes from the engine, but only at certain throttle position/RPM (when the throttle is open, little or no vacuum is present).

So cars will have a small plastic vacuum "ball" hidden somewhere inside, with a checkvalve. That ball will provide enough vacuum to keep the blend doors working.

But it's common for the ball to crack, or rub against something and develop a hole. Or check-valve can also fail. In all these cases, the doors will only move while throttle is closed, usually with higher rpm as well (so a quick blip of the throttle to get rpm up, and release throttle quick, resulting in higher RPM with throttle closed)

For ChickNorris' issue, since it happened immediately after replacing a heater core, I'd bet a vac line or electrical connector got disconnected or knocked loose.

So, removal, futzing & a new dash cover then?

Probably.

[Gman]

Many cars use vacuum to move the blend doors to determine where the air flows.

The vacuum comes from the engine, but only at certain throttle position/RPM (when the throttle is open, little or no vacuum is present).

So cars will have a small plastic vacuum "ball" hidden somewhere inside, with a checkvalve. That ball will provide enough vacuum to keep the blend doors working.

But it's common for the ball to crack, or rub against something and develop a hole. Or check-valve can also fail. In all these cases, the doors will only move while throttle is closed, usually with higher rpm as well (so a quick blip of the throttle to get rpm up, and release throttle quick, resulting in higher RPM with throttle closed)

For ChickNorris' issue, since it happened immediately after replacing a heater core, I'd bet a vac line or electrical connector got disconnected or knocked loose.

Could also be the control rod knocked out of place or broken blend door.

Found a video series that breaks down the components and access fairly well: