[GMC Jim]

When I went thru the air conditioning system on my truck; I repaired the temperature flapper door ; the outlets door (floor outlet/ dash outlets) and the bottom floor/defroster outlet door. The outside air inlet door and the recirculating air door were also not in the best of condition. I decided to keep it simple and eliminated both the outset air and the recirculating doors.. ( labeled 'valves' in the chassis service manual ) . I sealed the recirculating air door in the closed position and removed the outside air door. These modifications enables outside air at all times which simplfies the air choice option. The top lever of the dash control does also contol the vacuum to operate the doors. When the doors actions are modified as per above; the vacuum lines that used to operate the doors can be plugged or removed. This will result in the vacuum line going to the water valve only...... Jim

I did this mod over 10 years ago and have been well satisfied with the result. No more whistles and leaking air at the flappers and also if any smokers are riding in or driving, the outside air source keeps the cabin relatively clear....