Hi Leith,
The compressor consists of two major parts: electrical motor and mechanical pump. We can test only the motor windings.
Remove the start device from the compressor and measure resistance across all pairs of the terminals and across each terminal and the ground.
Normally it's supposed to be between 3 Ohms to 10 Ohms reading across terminals and ∞ reading across any of the terminals and the ground.
If there is nothing wrong you must replace the start device to check the condition of the mechanical part of the compressor.
Problems with the start devices are much more common than a faulty mechanical parts in such compressors.
- The part number for the start devise is
AP3885081
Gene.