The other problem is cooling. The freon and oil charge carry heat away
from the compressor which is probably why Glenn's tripped the thermal
switch. Before I got a "real" vacuum pump I used refrigeration
compressors successfully by cooling with a fan and constantly
lubricating thru a bleeder on the vacuum side with one of those air line
oilers made for lubing air tools. WD40 is not a very good lubricant for
this, I used light oil and sometimes even thinned motor oil with
kerosine. I also had an old airbrake compressor off a bus that I drove
with a 1 hp electric motor. I spite of the physics, I believe I could
have pulled 25 psi with it (maybe thru a worm hole from Jupiter). On
the output side she would put out 300 psi. All of this was back when
vacuum pumps were a lot more than $50 on Ebay.

Regards, Ron

PS. Fred, re-read my earlier post please. You will find it was
not directed at Glenn.