Max setting blows through defrost vents?

[420]

Since I've gotten the truck running again, I've noticed that when on Norm, everything is nice and cool, but when I switch it to Max, the air blows through the defrost vents toward the windshield. Anyone ever dealt with this before? I'm thinking the dash will have to come apart to address, but it would be really nice if there was a quick fix. lol.

 

[dgoodhue]

Re: Max setting blows through defrost vents?

You probably have a vacuum leak in your heater controls. When I had a leak it defaulted to the defroster.

 

[420]

Re: Max setting blows through defrost vents?

You probably have a vacuum leak in your heater controls. When I had a leak it defaulted to the defroster.

When that happened to you, was it only on max that it blew through the defrost vents, or on any setting?

 

[PJs97Talon]

Re: Max setting blows through defrost vents?

It may be causing a slight drop in the engine RPM just enough to allow the spring that would normally keep the defrost open by default to close the door. Maybe try bumping the RPM's a little and see if it changes anything. The other thing you can check is to make sure that the control cable is not loose or out of adjustment since you said you had the dash out.

 

[420]

Re: Max setting blows through defrost vents?

I don't think it is RPM related, because if the A/C is already blowing fine on norm, and I switch to max, it will still change up to the defrost vent, and there is no change in RPM.

As for a control cable, I have to admit I have NO clue what that is. Is that something the whole dash would have to come out again to get at? I wasn't the one who pulled the dash the first go around, and I am praying it doesn't have to come back out.

 

[dgoodhue]

Re: Max setting blows through defrost vents?

Mine did it all settings, I had vacuum leak from the main vacuum source.

 

[420]

Re: Max setting blows through defrost vents?

Yeah, vacuum leak was my first thought, but I figured if it blows correctly on Norm, it would be something else

 

[jguy]

Re: Max setting blows through defrost vents?

I have the same problem. AC blows cold, and through the correct positions, when I switch to max, it slowly moves to floor and defrost. I replaced the vacuum mode selector just for kicks, and nothing changed. Any help would be greatly appreciated.

Jimmy

 

[jguy]

Re: Max setting blows through defrost vents?

TTT, Anyone have any ideas?

 

[SY2455]

Re: Max setting blows through defrost vents?

Check the main vacuum line that is on the pass side of the intake. This line comes off a port in the front of the upper intake. Before I fixed this line on my truck it would come apart on the bottom where the plastic tube goes into the rubber vacuum line coming from the upper intake.