1. Lack of Preventive Maintenance
   PM is hard to sell by itself in this economy but you can always do your PM on every Service Call. Your customer will appreciate your efforts.
2. Key Components Not Changed
   Contactors and Relays which can cause motor burn.  Always check the compressor amp draw against the FLA of the compressor.
3. Dirty Condenser and Evaporators
   This is a PM item.  You cannot properly charge a system with a dirty condenser and/or evaporator
4. Worn Pulleys and Belts
   The number one overlooked A/C fault.  Always adjust the pulley then the belt then set blower amp draw close to full load amp draw of the motor with doors closed.
5. Low Refrigerant Charge
   This is the worst thing that can happen to an A/C system.  System icing always will damage the compressor.
6. Misadjusted Expansion Valve
   Poorly adjusted valves will cause liquid flood back thinning the oil and damaging the compressor.
7. Liquid and Oil Slug Upon Start Up
   Here a pump down system or adding a suction line accumulator is the best defense to preventing these conditions.
8. Liquid Floodback
   Preventing LF is as simple as cleaning the evaporator and filter and checking the Super Heat.  Super Heat should be no less than 20 deg at the compressor.  Compressors are meant to pump vapor.  Any liquid that reaches the cylinders of the compressor is a potential cause for damage.
9. Safety Controls
   Making sure that your low pressure switch doesn’t let your system run into a vacuum.
10. Mismatched Oils and Refrigerants
    Know  what oil is in the compressor and what refrigerant goes with that oil.   With over 100 refrigerants and basically 3 different oils, it is very likely that you can inadvertently mismatch the oil and refrigerant.

Probably the most important thing to remember is a well maintained electrical system and correct Super Heat at the compressor as a rule will almost always prevent costly compressor failures

For more information on developing a good PM program, call 1-800-743-6009