DIAGNOSIS BY REFRIGERANT PRESSURE


A/C system symptom
 Measurement circumstance
 Cause
 Measures
High pressure
 Low pressure
 Air outlet temperature
 Note
Cooler is not effective.
 Low
 High
 High
  • Pressure for low pressure side is high, and high pressure side is low.
  • When the A/C operation is stopped, the pressures of low pressure side and high pressure side immediately become identical.
  • Leakage inside compressor
  • Faulty compression of compressor
  1. Check according to the compressor check.

    1. When no foreign object is present to the oil, and when the colour is light grey, replace only the compressor.
    2. When foreign objects are mixed to the oil, and the colour is black, replace the compressor and receiver.
  2. Perform the evacuation sufficiently to remove the foreign objects and moisture in the cycle.
  3. Fill the new gas to the specified amount.
High
 High
 High
  • Low pressure side/high pressure side pressure is too high.
  • Low pressure side piping is too hot to touch.
  • Air is mixed to the refrigerant cycle.
  • Evacuation is insufficient.
  1. Perform the evacuation sufficiently, and remove the foreign objects and moisture in the cycle.
  2. Fill the new gas to the specified amount.
Sufficient cooling and insufficient cooling occur periodically.
 Fluctuation
 Fluctuation
 Fluctuation
 During the air conditioner operation, the low pressure side pressure alternates between the negative pressure and normal. (also in the high pressure side, the abnormal and normal statuses are alternated).
 The moisture in the refrigerant cycle becomes frozen in the expansion valve, then the circulation of refrigerant is stopped temporarily. Subsequently, the status recovers to normal by the melting of ice.
  1. Replace the receiver (drier).
  2. Perform the evacuation sufficiently, and remove the moisture in the cycle.
  3. Fill the new refrigerant to the specified amount.
Cooler is sometimes not effective. (works occasionally)
 Low
 Vacuum
 Fluctuation
  • The low pressure side pressure indicates the vacuum, and the high pressure side indicates the low pressure.
  • To the piping before and after the expansion valve, frost or dew is observed.
  • The foreign objects or moisture inside the refrigerant cycle deposits or
    freezes inside the expansion valve, and the refrigerant flow is disturbed.
  • Because of the expansion valve operation failure, the refrigerant flow is disturbed.
  1. Check the expansion valve.

    1. If foreign objects are present inside the expansion valve, remove them by using an air gun or others.
    2. When no foreign object is present, the expansion valve operation failure is suspected. Therefore, replace the expansion valve.
  2. Perform the evacuation sufficiently, and remove the foreign objects and moisture in the cycle.
  3. Fill the new refrigerant to the specified amount.
Cooling effectiveness is bad.
 Low
 Low
 Slightly high
  • Low pressure side/high pressure side pressure is low.
  • Outlet air temperature is high.
  • Gas leakage is present to somewhere in the refrigerant cycle.
  • Refrigerant gas amount is insufficient.
  1. When the pressure gauge indication is close to zero, check the leak position, and then repair the leakage. Also, when the value is lower than the standard pressure, check if the gas leakage is present, and repair if necessary.
  2. After checking the leak position, sufficiently perform the evacuation, then fill the new gas to the specified amount.
High
 High
 Slightly high
 Low pressure side/high pressure side pressure is too high.
  • Refrigerant amount is excessive.
  • Condenser cooling is insufficient.
  1. Clean the condenser fin (fouling, fin clogging)
  2. Check the condenser fan motor (radiator fan) operation.
  3. When 1 and 2 are normal, recover all the refrigerant. Then, perform a sufficient evacuation again, and fill the new gas to the specified amount.
High
 High
 High
  • Low pressure side/high pressure side pressure is too high.
  • Frost or dew is formed to the low pressure side.

 Expansion valve trouble (valve opened excessively)
 Replace the expansion valve.
Normal
 Normal
 Slightly high
 -
 Because of the slight difference of measurement environment, secular change of vehicle, or others, it is possible that the outlet temperature fluctuation has occurred.
 Check the status for a while, and if the status does not improve, recover all the refrigerant, then fill to the appropriate amount.

COMPRESSOR CHECK


Trouble symptom
 Check method/circumstance
 Cause
 Measures
Abnormal noise from compressor main body at A/C operation (rattling noise)
  • Refrigerant cycle gauge pressure check

  1. Low pressure side/high pressure side pressure is high.
  2. Pressure hunting occurs.

 Abnormal noise due to excessive refrigerant charging
 Fill an appropriate amount of refrigerant.

  • Check the refrigerant cycle gauge pressure. When the pressure difference between the low pressure side and high pressure side is small, remove the compressor oil, and perform the oil judgment.

 Damage to inside the compressor

Compressor malfunction (belt slip)
 Check the compressor rotation, and if a seizure or sticking is present, remove the compressor oil, then perform a judgment.