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Compressor Overheating:
Compressors generate heat from the electrical motor, friction between different
moving parts and heat of compression. When the compressor is running outside its
operating envelope or its design conditions that is when problems begin.
What can cause overheat:
• High discharge temperatures
• High compression ratios
• High superheat
• Inadequate motor cooling
• High return gas
• Lack of external cooling
Overheating occurs anytime when oil in the compressor is heated so much that it will lose
its ability to lubricate >300F/149C
How to prevent Overheating:
• Always check the discharge temperature 6" or 150mm from the discharge
service valve and make sure you stay below 225F/107C Semi-Hermetics.
Other compressors like Reciprocating Hermetic, Scrolls, Rotary, Screw will
have different values so you will need to check the manufacture manual for
those numbers. Example, some Scroll you want to keep them below
260F/127C. If your above 225F/107C you need to investigate why.
• You want to make sure you maintain compression ratios per design. Copeland
Scroll Compressor for AC have a max of 11:1 before the floating seal unload
and refrigeration Scrolls are 26:1.
• Make sure you set minimum superheat so your return gas temperature back at
the compressor is not so high that the oil starts to lose its lubrication abilities
(POE - 300F/149C) or breakdown (POE - 350F/177C)
• Always insulate the suction line because if it is not insulated it will pick up all
the heat in the space and bring it back to the compressor.
• Properly set low pressure control so that system does not take a very long time
to pump down or run the compressor outside the compressor envelope.
• Make sure the Condenser is clean and there are no pressure drops in the
suction line
• Have the correct charge in the system so the refrigerant coming back can cool
the compressor motor and stator.
• Use required cooling methods like head cooling fan, demand cooling or liquid
injection when required by compressor manufacture
