"OEM" or Original Equipment Manufactured Parts are the parts that are used to create your air conditioning unit during its initial production. Can you use a generic replacement part? Sometimes you can, but typically these parts do not fit, function or operate your unit to its full and best capabilities. Many times generic parts require 'modification' to even fit or function at all. An OEM part also helps you maintain your warranty on the equipment you are working on.

An air conditioner that has a 5 year warranty on its sealed system (compressor, coil, expansion valve, etc.) may require you to use OEM parts when repairing other components of the unit prior to needing a compressor replaced. If the thermostat, switch, motor or other parts of that unit are not replaced with OEM parts when repairing the unit they may not provide the proper total system function necessary for the compressor to maintain its function.

Consequently, the remaining warranty on the unit may be voided. You wouldn't want your doctor to replace your heart with a bicycle pump, (especially if a human heart was available) would you?! Why would you want to do something like that to your air conditioner? Be sure to ALWAYS use OEM parts for the job.