91' vert AC problem

Hey guys my Dad just bought a 91' LeBaron convertible. The AC works, but as soon as you accelerate it shuts off the dash vents and blows from the floor vents. Slow down and stop and it blows from the dash again. We checked all the vacuum lines and everything seems to be fine with no leaks and hooked up where it belongs. We also replaced the check valve on the vacuum line on the booster. No luck. Any suggestions before we go ripping the dash out? Thanks.

I once had a 1991 Dodge Shadow coupe that did the same thing brand new. There is no need to rip the dash apart because the problem is not there. The check valve to the power brake booster has no effect on the vent system so replacement of that valve was a useless effort.

What is happening is that there is either no check valve or a disfunctional check valve between the vacuum sourse to your vent system and the vent system itself. Everytime you accelerate and drop manifold vacuum, the vents redirect on that loss of vacuum.

Trace the vacuum lines under the hood between the vent system and the sourse of vacuum. If no check valve exists, buy one and install. If you find one there, replace it.

Let us know what you find and what you do.

Yes KManiac is right.

However, ripping out the dash is very simple on most EEKs including the 91 LeBaron. There's 4 or 5 3/8"/10mm bolts on the top, right where the dash meets the windshield, then one 1/2"/13mm bolt/nut on each side by the doors, accessible from below the dash, and then there's 2 nuts holding the steering column up, and that's about it. The hard part is getting the dash to move more than 12 inches or so back, all the wires prevent it from moving very much.