Mode door adjustment

[1970pelle]

Installed the new heater core in the 86 C10 today.It has turn into a bigger job than just the core.Appears to have been leaking for sometime.The carpet pad was soaked and the floor on the passenger side has rusted.During clean up found about six very small holes.So pulled the seat, cleaned everything.Will start tomorrow on welding in repair panel.But I did finish up the core,new heater hoses,thermostat,flush.repaired overflow nipple on radiator.Fell off.But I screwed up the adjustment on the mode door.The arm fell off.Does anyone have the adjustment prosedure from the service manual??My has factory air.Vacuum operated mode doors.Thanks Ken

[shadetree]

ttt

[1970pelle]

Anybody have a service manual?Need A/C mode door adjustment procedure

[1970pelle]

Anybody have a Factory service manual?????.Please Need adjustment info for mode door.

[75gmck25]

From my '75 manual:

Loosen the screw that holds the cable end in the bracket on top of the plenum. Then put the temp lever in full cold, and retighten the screw. That's it.

Bruce

[1970pelle]

Thanks but my truck has vacuum operated mode doors.Its a no brainer on the temp door cable adjustment.The mode door system has 2 doors.A main door for when switched to the max air postion.And a secondary door.That operates off the same rod controlled by the single mode door actuator.There is a adjustment at the second door connection.There is very little room for error because the door will rub and or bind.I would have taken a photo if I know this was such an unknown topic.I'm going to get a factory service manual.Been watching the E-bay.Just thought I might get a little help.Thanks

[1970pelle]

I'll try one last time.There are several doors inside the HVAC box.(!) is the temp door which is cable operated,The temp door controls air temp from heater core and if it has A/C the evap coil.(2) is the mode door which on newer trucks is vacuum operated.The actuator uses control rods that are adjustable to control the doors.The mode door controls air flow through the dash deforost,vent,bil-level,floor.If anyone has a factory service manual I need the adjustment procedure for the mode door mainly the secondy door.please!!!

[75gmck25]

I have a factory service manual for my '75. I've looked at my manual and it does not have a procedure for what you are trying to adjust. I removed and reinstalled my entire heater/AC assembly and never had to adjust the vacuum actuators. Maybe I was just lucky.

I have also looked at a large number of 73-87 trucks in the junkyard, and the plenum arrangement and vacuum operated doors have always looked about the same for every A/C-equipped truck (all A/C C-K trucks have vacuum operated mode doors). However, I have learned over the years that there can be signficant over the years, and some changes are hard to see. Maybe your truck has a different door arrangement inside the plenum.


Bruce

[1970pelle]

Here is a picture of the top of my HVAC box installed in truck.With glove box and dash pad removed.The rod in ? is in the picture.The rod is controled by a vacuum actuator that has correct vacuum supply no leaks,kinks ect.The the actuator connects to the door pictured.The door has a lever on top of the door.The rod from point A connects to a second door at point B.And you can see this connection is adjustable.Because if these adjust is not correct the two door will hit each other.Even if some on could messure the rod on there truck it would get me a starting point.I have it some what close.But I want it prefect.

[75gmck25]

I remember watching the two doors move in the plenum, and swing by each other. It appeared to be a two-stage process, where the mechanism moves one door first, and then reaches a pivot point where it starts moving the other door.

I looked at the mechanism on my '75 truck. It works generally the same as the one you took a picture of, but instead of a threaded rod it has a flat metal rod that slides back and forth into the end bracket for adjustment. You slide it to the right length and then screw down a set screw to hold the adjustment. I'm not sure if there are other differences that aren't obvious.

I rechecked my GMC service manual. There are a lot of diagrams, but no adjustment procedure in the 74/75 manual.

Bruce

[1970pelle]

I'll give it a try.Thank you very much!!!!