Anyone have a picture of AC ducting under the dash?

[zieg85]

I am going to do some long needed repairs on the old girl 1985 C20 factory AC in and under the dash... My question is, I don't get full defrost so I am thinking an actuator or door is stuck.  Vent is fine but when I put it to defrost I still get some air out the vents.  Any diagrams would be helpful as well.

[VileZambonie]

Are your vacuum lines all connected? Is the vacuum reserve cannister hooked up in the engine compartment?

[zieg85]

Yes and yes.  No vacuum leaks that I hear and you can actually hear the ducts opening and closing when going from vent to floor to defrost, vent is full, but I get a mix of vent and defrost on defrost.

[VileZambonie]

I'm too beat to search right now but I posted hvac pix on here a while back for someone else. If you feel like searching I believe I scanned them out of the factory service manual. If you don't find them remond me tomorrow and I will try to get them for you.

[zieg85]

Thanks, have a great evening...

[beastie_3]

You could also have debris blocking the door from opening/shutting completely. I did with mine. The foam seals from the ducting eventually came off and found its way down. I took the complete box out as well as the ducting. It really wasn't that hard. You could do it all in a few hours. I took off the dash pad and instrument panel, glove box and ash tray to have complete access as well as to look around for anything else that might need attention. The passenger compartment box comes out as one unit after you unbolt and unscrew it from the outside of the firewall as well as take off the heater hoses. Lay it down on the floor and unhook the vacuum hoses and cables. I completely took the box apart, it comes apart in a few pieces. I put on new foam seals where the old stuff was and cleaned out all the debris. Food for thought.

[Grim 82]

If its dividing airflow between the vent and defrost something is holding up the second trap door. It's either debris like beastie said or its not getting enough vacuum to the diaphragm. Also check that the hinge pin on the door didn't pop out of the hole in the duct. If you tear it all apart so that you can see it, you can run the truck and work the switch to see and hear what its doing. My ductwork was all different kinds of wrong when I got it, and filled with mice, but I found almost a dollar in change and a handful of .22 shells when I took it apart.