Mr John,
RobinAir makes a good unit.
But they have several.
Do not buy the cheapest.
It will take you till the cows come home to get a good vacuum.
I have a comercial pump.
It cost $395.00
It takes 20 minutes to get  -30 BAR
Find a Snap On truck travel down the road.
Stop him.
He will have good unit to do  job.
Good Evening,

Fred.

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Subject: A/C help needed
I need to put a new drier on my A/C and re-evacuate the system. Any
ideas as to make/model number/source of vacuum pump that will do the
job?
John Lauterbach
Macon, GA
'84 7-passenger