1: This video indicates that you can check for voltage drop with a Multi-meter!
Sadly there are some ‘self appointed refrigeration Gurus who at times make very misleading statements on boating forums. Recently one such claim was that you can’t check for system’s DC supply voltage drop with a multi-meter. Absolute rubbish.
This test is presented in an attempt to expose that ‘Fake News!
The test cabinet has a Danfoss BD50 12VDC compressor. This video shows how the supply voltage can easily be read before and as the compressor starts / tries to start, so as to indicate if the power supply is adequate.
Question being: Is the supply voltage dropping sufficiently to cause the Motor Driver Module to default into either low voltage or over current mode.
A multi meter used this way will not determine if the Motor Driver (Black box on side of the compressor) is faulty or not, but it will indicate if there is the possibility of a bad power supply, (Battery or supply lines) something which is the most common cause of a compressor failure to run situation. This may prevent a Motor Driver Module being replaced unnecessarily.
To check voltage simply put the your Multi-meter to DC volts and the two test lead prongs onto where the DC power connects to the compressor. Usually the top two terminals on the Motor Driver Module. Take note of voltage before and while starting / attempting start. If the difference is more than one amp then I suggest upgrading the power supply / battery.
Note: A high voltage reading with no load is irrelevant, it is what is available when the load is applied. (motor starting etc.,)
Now I don’t have Superman’s eyesight but even I can see and read the voltage drop indicated on the MULTI-METER….!