Join Date: Jun 2007
Location: Southern Maryland
Thanked 1 Time in 1 Post
I don't claim to be an expert butt, here is what I do know to be factual. I currently drive a 1986 for a DD and it has three control cables, 1 for heat/vent, (vent being fresh air only, noooooo vacuum control on this one) 1 cable for defrost, and 1 for the amount of heat being introducted into the cab via the defrost or floor heat. I just sold my 1987 and 1988 YJ's, both had the vacuum/slide controls. the reason you can't see the vacuum actuator is its behind the dash panel just below the windshield ledge, it just controls/open-closing of the damper for the outside air. I still own a 1989 with a 4.2/MPI and a 1990 with a 302/V-8 and they both have the same heater controls as the 87-88 have and work the same way. When you want heat the fan blows air to the floor and pulls ouside air in across the heater core, when you want defrost the fan blows air to the windshield and pulls outside air in across the heater core, when you want vent it shuts down the fan and it pulls fresh air in from the outside inlet (only while you are moving forward) and out throught the open door on the passenger side. When you turn the slide controls to off it closes the outside air vent and inside vent door, shuts down the fan whether the fan switch is on or not. I hope this answers your questions.
"Sometimes Insanity and Genius walk the same side of the street"