Analogue insulation tester Sanwa PDM5219s

[Radhe]

I just bought this analogue insulation tester for testing compressors. I have a digital yokogawa insulation tester as well but I prefer an analogue tester. I wanted pointers on deciphering needle movement in an analogue meter. I have a compressor that is kinda loud but seems to be cooling ok. I do suspect some issue with it so tested it with both meters and with analogue the needle jumps to 20m ohm and falls back to infinity but with the digital one it just indicates OL on all three terminals on the compressor. I did get a 0 m ohm reading on one terminal once it never did it again.
How to do interpret readings of an analogue Megger is my first question and. Any pointers or article to on analogue readings.
Thanks

[NH3LVR]

Welcome to the Forum Radhe!

I have a Analog Yokogawa I purchased in 1982 and used until I retired last year. I have never had a Digital.
Someone posted a test scenario for Hermetics a short while back (or a link to one) but I did not locate it. It was much more involved than my practices.
The initial low reading is caused by Capacitance. Once the windings are charged the Megger will give a true reading.
Be certain that all other leads are disconnected so you are testing only the Motor windings. Bad things can happen if you apply the voltage to Semiconductor devices.
Never test a Hermetic in a Vacuum!
I generally use a figure of One Megohm before I become concerned. Others with more Hermetic experience may disagree.
Why you get a Open Lead with the Digital I cannot say.
A Megger is a very useful tool. Having spent a lot of time in Production Plants doing other than refrigeration I have found many uses, especially in wet areas.
These include testing flexible cords for leakage and motor wiring in conduit.