My 98's air conditioning cuts out when travelling uphill and cuts back on when going back down. Weird huh? I think it might have something to do with the flapper door. Any ideas?
Thanks!

 

There is less vacuum when the throttle is opened more while going up hill, I bet the air starts blowing through the defrost ducts. Check the vacuum resevoir under the battery tray for leaks.

 

yes it does start blowing through the defrost ducts. Thanks again! I'll take a look this evening.

 

Mine did that too, and I had no vacuum leaks but I never found a check valve in the line. If there is no check valve the engine basically steals all the vacuum when under heavy load. I installed my check valve in the supply line right at the intake manifold. I had a check valve laying around from another vehicle.

 

I have just had that very same problem with my 97 GC. I was poking around under the hood and the vacume line that went under the battery fell off when I touched it. Cut off a bit of the end, and reattach it, use a small zip-tie for a clamp. That not only solved the A/C uphill problem, but got my cruise control working.

 

The same thing happened to me yesterday when I was pulling a big hill. I had cruise control on too and it also stopped working briefly (i.e. I started slowing down...)