Diagnosing Compressor Problems : Inefficient Compressors

 Inefficient Compressors:

• Characterized by high suction pressure and low head (discharge) pressure.

• Occurs when the compressor is not pumping the proper amount of vapor.

• Tell-tale Sign:

• Use a clamp-on ammeter on the compressor; inefficient compressors typically have lower than normal amperage.

Causes:

• Broken Suction or Discharge Reed Valves:

• Causes head pressure to fall and suction pressure to rise.

• Example: A broken discharge valve prevents proper compression, leading to high suction and low discharge pressure.

• Damage Causes: Overheating or slugging.

• Worn Pistons or Compressor Rings:

• Discharge gas blows by the piston, pressurizing the crankcase.

• Causes head pressure to fall and suction pressure to rise.

• Damage Causes: Overheating or floodback.

• Blown Head Gasket:

• Refrigerant leaks from the head gasket into the suction line.

• Causes high suction and low head pressure.

• Common Cause: Liquid slugging.

Testing for Inefficient Compressors:

• Attach a pressure gauge to the suction service valve with the compressor running.

• Reciprocating Compressors: Should pull a minimum of 25 inches of mercury vacuum.

• Rotary Compressors: Should pull a minimum of 29 inches of mercury vacuum.

• If the compressor cannot reach these vacuum levels, it indicates internal damage.

• Additional Check:

• After reaching the vacuum level, turn off the compressor and verify if the level holds.

• If pressure rises above the vacuum level, it indicates a weak compressor with a possible internal leak.

• Important Note:

• Do not attempt this test on scroll compressors as it can damage the fusite element.