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I need to know a vacuum diagram for my 92 7.3 IDI. I am told I have a vacuum leak in my cooling system. All my cold air from the air conditioner is coming all out of my defroster vent and not out the other vents. How should I track this down and find the leak?
If your heater controls are similar to mine a vacuum line passes through the firewall beneath the heater hoses and crosses from behind the glove box to the center of the dash.
The control unit might not be getting vacuum, or the vacuum motor (servo) that controls the door inside the ductwork may have a ruptured/torn diaphragm.
Do you have MityVac or similar tool that can be used to apply vacuum and also has a gauge so you can tell that the system is holding vacuum?
Are you sure that the door itself is not jammed, or the hinge is not torn?
You have a diesel and I am not familiar with how your truck provides/stores vacuum, but these are the basics of the climate control system...in my truck at least.