Glenn Ashmore wrote:

The problem is lubrication. Refrigerators circulate oil with the
refrigerant to keep the compressor lubricated. When you use it as a
vacuum pump there is no oil. You can extend the life a little by
squirting a little WD40 in the intake before each session but that is
of limited value when the compressor runs 4 or 5 hours at a time.

If you're using WD-40 as a lubricant, that's a major part of the
problem. WD-40 is a good water-displacer, but its performance as a
lubricant is abysmal. From perusing the sites for DIY vacuum systems, it
appears that the preferred lubricant for refrigeration pumps is ATF
(automatic transmission fluid). All things considered, $50 or so for a
Gast vacuum pump on Ebay seems like a better way to go.

--
Regards

Brian