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.
I suspect that the older compressors last longer because they are built
"looser". As refrigerators got more energy efficient the compressors
have been built to closer and closer tolerances so constant lubrication
became more critical.
I made a high vacuum system back in science fair days out of an old
pre-WWII Kenvinator compressor and used it for several projects. When I
started doing woodwork I used it to bag veneers for several years. When
it finally died I tried several newer compressors but none lasted more
than a couple of sessions. They would run for 10 or 15 minutes and then
the thermal switch would kick them off. Ruined a lot of expensive
veneer trying to figure a way to keep them running.
There are at least 50 vacuum pumps on eBay right now that would be ideal
for vacuum bagging. All under $100 and many under $50. Not a bad price
considering that if a refrigerator compressor craps out in the middle of
a session you could ruin that much material or more.
Here are a few that would work.
http://cgi.ebay.com/ws/eBayISAPI.dll...tegory=11 773
http://cgi.ebay.com/ws/eBayISAPI.dll...tegory=26 236
http://cgi.ebay.com/ws/eBayISAPI.dll...tegory=26 236
http://cgi.ebay.com/ws/eBayISAPI.dll...tegory=46 547
http://cgi.ebay.com/ws/eBayISAPI.dll...tegory=46 548
Here is a perfect setup complete with flow guages and tank:
http://cgi.ebay.com/ws/eBayISAPI.dll...ategory=73 21
William R. Watt wrote:
From what GA wrote it would be better to look for an older unit than a
later one as I assumed. It could be tested with a car vacuum guage. A
vaccum guage costs about $15 at Canadian Tire. I found one at a garage
sale last summer for $4 which included a timing light and a remote starter
switch.
As for burnout maybe the compressor doesn't have to run at full power.
Perhaps a light dimmer switch could be used to set it at the speed needed
to maintain the vacuum for the particular application. Or 2-3 compressors
could be hooked up together and run at lower power off the same dimmer switch.
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