I was just wondering what this vac line is for on my 89 YJ 4.2 . It comes of the intake manifold near the firewall and is tee'd. One leg of the tee goes to the other side of the block for the axle disconnect etc., but the other leg has what I think is a check valve and then goes thru the firewall just above the level of the manifold. the line is one of those plastic ones red in color. Just curious as to what it is for as I can't seem to find it on any diagram.
Usually on YJs and XJs, the red vac line is the main supply to the transfer case switch for the front axle disconnect. From the switch, green is for 2wd , yellow is for 4wd and blue is a vent that terminates at a check valve.[img]/wwwthreads_images/icons/smile.gif[/img]
This vac line is definitely not for the transfer case, that one is on the other side of the motor. If its for the heater controls, what requires vacuum to work? I thought it was all done by the lever switches in the dash.
On my 89 YJ, the vacuum line through the firewall connects to a switch that controls which fan turns on. When the switch is activated the AC fan works, when deactivated the fan for the heater/vent works.