Hi,

My basic question is: Should a vacuum pump hold a vacuum after it has been turned off or is an in-line valve required?

My next question is: Is there a troubleshooting procedure to isolate a problem with the vacuum pump and gauge set with just those two tools?

I just acquired an inexpensive 7 cfm / 100 micron vacuum pump (looks new but no label or manufacturer - kind of like Master Cool) and a 134a gauge set (aluminum body but like above - no ID).

Here are two photos but since I can't post active URLs you'll need to paste these to your browser's address line and remove the spaces between h t t p.

Label on vacuum pump: h t t p://s225.photobucket.com/albums/dd163/Keps-Photos/Heater%20-%20AC/AC%20Tools/?action=view&current=VPTag.jpg

Picture of setup that I used: h t t p://s225.photobucket.com/albums/dd163/Keps-Photos/Heater%20-%20AC/AC%20Tools/?action=view&current=VPTest.jpg

To test the vacuum pump and gauge set out I filled up the oil, hooked the yellow gauge line directly to the vacuum pump and turned it on, opened the LO gauge valve, closed the HI valve and evacuated for about 10 mins (the gauge pegged out immediately). When I turned the pump off (but left the LO gauge valve open) the "system" seemed to hold the vacuum for a couple of minutes and then began to loose it at a faster and faster rate until I was back to ambient pressure in less than a couple of minutes . (I presume that whatever was leaking was doing so immediately but since my gauges don’t show very fine changes it just didn’t read right away.) I tightened all the screw fittings tightly by hand and ran the test with the LO hose both connected to and disconnected from the “dead head” fitting on the side of the gauge set.

Sorry to bother you folks with such a basic question but I haven’t found any reference to this yet and need to determine if I should return the pump. ( I know that I have an issue with the high side snap fitting.)

Kep