Air Conditioning Compressor Noise Upon Initial Operation (SI-0011)

AIR CONDITIONING COMPRESSOR NOISE UPON INITIAL OPERATION

TECHNICAL SERVICE BULLETIN

SERVICE INFORMATION

This information bulletin has been developed to advise the technician of a normal  condition with A/C compressor operation when the compressor has been inoperative and allowed to cool. The condition is described as a knocking sound upon initial compressor operation that will quickly dissipate.

Do Not replace  the compressor in an attempt to correct this condition. The condition is normal and will not be eliminated by compressor replacement. When you have such a complaint from your customer, please explain compressor operation to the customer.

DESCRIPTION OF SYSTEM OPERATION UNDER THIS CONDITION

1. Under ideal conditions, a low temperature/low pressure gas enters into the A/C compressor, and by way of compression, the gas will change to a high temperature/high pressure gas that is discharged into the system.
2. Refrigerant is in a gaseous state for the time that it is above the saturation line, if the temperature is allowed for any reason to fall below the saturation line the refrigerant will become a liquid.
   1. Notice at 0.8MPa and 80 degrees Celsius, the high temperature gas cools, becoming a lower temperature gas, and eventually as it falls below the saturation line becomes a liquid denoted by the green arrow becoming solid.
3. If the A/C compressor has been inoperative and allowed to cool, the refrigerant will also cool, and liquid refrigerant can form within the compression chamber.
4. Under this condition, when the A/C compressor begins to operate it is trying to compress liquid refrigerant; Liquids can not be compressed and will temporarily create the knocking sound.
5. After initial A/C compressor operation the sound will dissipate and no longer exist.
   1. At initial A/C compressor operation, the compressor will attempt to compress any liquid refrigerant that may have accumulated in the compression chamber and create a knock sound.
   2. By means of the liquid refrigerant being quickly discharged out of the compression chamber via the discharge valves, liquid refrigerant will no longer be in the compression chamber and the knock will no longer exist.