"I have a 91 jeep Cherokee, and the four wheel drive is not working. I believe it is the actuator in the front axel. I have vacume to the actuator. Is there suppose to be vacume on both lines going to the actuator? I currently do not have that. The frotn drive axel turns but the front wheels will not engage.
Shift to 2WD position. Locate vacuum switch on front of transfer case. Apply 15 in. Hg vacuum to "L". See Fig. 1. Vacuum should be present at "M". Connect a vacuum gauge to "N". Shift to 4WD position. Apply
vacuum to "L". Vacuum should be present at "N". If switch fails any test, replace switch. Pic included