A/C controls
 

I have a 1988 cherokee and eveything works with the A/C but the selector on the dash. the ac blows cold air but it will not blow out the vents. it will only blow out the defrost. Can anyone help with this problem?

behind the front bumper pass side there is a vacuum storage ball/canister with two lines on tit trace both lines for broken/cracked places most common spot is beside the battery

Something's up with the vacuum lines. Unsure how they're routed on an '88, but definitely start tracing them to see if something came unplugged.

On my '00, I had to cycle through the controls a few times with the car running (to pull the vacuum) to get it to work properly after I put the dash back together. On mine there is an additional vacuum line that reaches through the firewall between the A/C lines and heater core lines that fits into a "T". I've seen quite a few forget about that one.

Just dealt with this same issue in my 97. In mine I had a break in the vacuum line from resting on the heater hoses where it went in the firewall. After repairing that I had vacuum back to the controls but it still wasn't working. I took the controls apart and found that the vacuum holes in that little plastic circle piece in the back of the control switch were clogged and taking it out and cleaning them out with a pin solved it.

i just had the same problem. the line running to the ball canister behind the bumper was broke. it broke off flush with the rubber elbow that connects to the canister but was still sitting in line with the elbow. when i touched it moved and i could hear the vacuum. i pulled the broken piece from the elbow with a small pair of needle nose pliers. then i pushed the line into the elbow. everything works now. thanks for pointing this out.