Been fighting this problem since I first got the truck running. 88 Jeep comanche 4.0 5speed 2wd, factory ac. Seems that when ever I rev the engine or its under high load my ac will change from max, normal, bi lev, vent, or heat directly to defrost. I've had quite a lot of problems with the climate controls in the manche. Still likes to melt the fuse while the ac is on no matter the fan speed. Could it be a problem with vacuum? I still have my vacuum reservoir and there's no noticeable vacuum leaks under the hood. It will switch settings without problems and heat works great. Any advice will be very helpful.

 

The piping/hoses near the battery get trashed. You can't see them easily. You need to put more effort into finding your vacuum leak.

 

Not sure if your camanche is same as wagoneer and cherokee's. But if so it should have a vacuum can/tank mounted under the bumper on right side. I used 2 vacuum cans from a 85 wagoneer and relocated too the passenger side fender well. It eliminated a good amout of vacuum lines (less lines less leaks) I removed the coolent tank and bracket. And mounted them with self tapping screws.

 

They ARE the same.

 

I'll inspect my vacuum lines today. I do have the vacuum ball still which I am going to relocate to under the coolant tank.

 

Doing that will most likely solve your problem. If not, post back up.

 

Well think I solved the problem, other day I had to bypass the vacuum ball to get air to not come out the defrost. Today I finally got to work by relocating the vac ball. Found it full of water. Drilled a hole and drained it. Sealed the hole up and then I found a hole in the vac line 3 inches from the firewall which is where it had been sucking water from when the comanche overheated earlier the day I had to bypass the vac ball. I have yet to test the fix cause I've been letting the flex seal cure on the pressure bottle.

 

You and your frickin Flex-Seal!! LOL. Worked like crap on my patio roof!!. Get a new ball at the JY.

 

The old ball is just fine. I used a screw to plug the hole and not the flex seal. My first time using the stuff. Thought I'd give it a try. So far seems pretty good stuff. Time will tell.