gsxr750

You only need a vacuum pump if you intend on flushing out the entire system and refill it with new oil and r134.

You don't need a vacuum pump to release gas under pressure, there is a simple shrader air valve stem that releases gas on the low side ac charging port, the r134a should be properly reclaimed to avoid release into the environment, the professionals have a system that reclaims the gas and they clean & reuse the old r134a .

If your only recharging the system, you don't need a vacuum pump. If your only recharging a system release of r134a into the environment shouldn't even happen, if done properly, unless your system has a big leak.

The only difference with the professionals with the more elaborate tools, will recharge the AC from the high side, as compared to the home garage method of charging from the low side, for consumer safety.

First thing to do would be to recharge the system with 1 can of r134a leak detector and another can of r134a gas, then run the AC and check for leaks. You can do this for around $30 with autozone products.