View Full Version : Detecting moisture in a refrigeration system by electrical current

26-02-2013, 05:24 AM
Dear All,

I am not an electrical expert!! I read an article about detecting moisture and I am not sure that this method works or not.

The method is like this : a megger device passes around 600 volts of DC current into compressor windings and if there is moisture in the crankcase then there will be electrical current passing through the compressor body.

Have anybody used this method? Does it work?

Thanks for your replies.


28-02-2013, 07:59 PM
I am not an expert, but this is a method to detect moisture or a short circuit in an electro motor.
it can not be used to detect whether or not there is moisture in the refrigerant.

You use a megger to check the integrity of the windings of a motor, if I remember correctly, you plave one pin on U1 and the other to earth and then press the test button and get a certain reading (should be unlimited to x volts) then V1 and then W1 and perform the same check. if there is a to high reading on any of them, that means the windings in the motor has too much conductivity to the body of the motor (the copper that is stationary in the body of the electro motor has "shorted" with the body)

In cases where the motor has been "under water" or in a high condensation environment, it might help to spray the inside of the motor with "Electro clean" and heat it with a heating fan, to drive out the condensation.

but again, I am not an electro guy, just a mechanic trying to get by :)

01-03-2013, 06:32 AM
Hi Lana
Sure it works! 10 or more years ago I had a motor tested, water pump not compressor. The tester came back and said it was what they referred to as a "damp motor" it had 2 meg and was still running, the mark should have been bellow 1 meg. Due to a big water leak the motor was saturated in water for at least 24 hours and tripped on current but ran after a few days of drying without any problems. So measuring the resistance between windings indicates moisture. Also I think current passing through/between the windings as well as the body.

16-03-2013, 03:54 AM
Hi guys,

Sorry for the late check in!!

Thanks a lot for your inputs.


16-03-2013, 05:30 AM
Hi Lana just to add some more on the topic. When I was a boy learning at school they taught us not to try to start a compressor whilst it was on a vacuum because an arc can be drawn 300mm in a vacuum of 25" with 240Vac. This is how some light bulbs work too.

16-03-2013, 05:34 AM
Thanks again.