Automotive Air Conditioning Information Forum

Correct.
Do a search on my name and look at the pic of the vacuum tree I set up. This allows you to pull down the car, vac pump, the tank hose, and the vac gauge with each having its own shutoff. Many techs do this, especially residential techs. The 4-port MGS allows you to connect the vac pump, but not the other stuff. You need some TEES and valves

Agree with Tim on Santech quality

Lots of pumps can get to 400 microns on their own, with fresh oil. I have a little clunker that was sold by MAC Tools at one time. Motor & pump about 4" diameter. Dead end against a clean micron gauge it will pull below 400 microns. But, connected to a system it will take hours to do the job.

All systems leak. Might me a molecule per hour, might be an ounce. Gauge valve stem seals, service valve seals etc. can all leak. So a large 1hp pump can sort of cover the smaller leaks up too.

Using a micron gauge is good practice. Dead end it on the pump occasionally to test the pump. Keep it clean. Oil or solvent wetting the thermistor inside will cause erratic or poor readings.

If you are buying a used pump to get started, evaluate the pump with the micron gage. Then change the oil and test again.

Best of luck with your business venture.