I have a 1987 XJ Laredo. 4.0 with aotumatic. 4 x 4. Ive just rebuilt the A/C system with new compressor, new condensor , new drier and thermostat. my question is when you accelerate the A/C system blower goes to very low speed until I reduce throttle. Im assuming engine vacuum has something to do with this.
Does anyone know the reason for this and is there a bypass?

What you're describing as going to "very low speed" is probably going from MAX to defrost which is the default mode when the system loses vacuum. There is no bypass. Just fix the system. Thoroughly inspect your vacuum lines and vacuum canister (behind the bumper) and find the leak.

Thanks downs. You were correct sir, broken vacuum line.

Just for fun.