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Diagnostic Table

  1. 1.

    Use the following table to guide diagnosis of the refrigerant system if operating pressures are outside normal limits.
    High (Discharge) Pressure Low (Suction) Pressure Component - Causes
    High Normal to High Condenser - inadequate airflow
    Engine - overheating
    Normal to High Normal Refrigerant overcharge - air in refrigerant
    Normal to Low High A/C Compressor - low performance
    Normal to Low Normal to High A/C suction line - partially restricted or plugged. (1)
    Normal to Low Low (2)
    Low refrigerant charge - leak in system
    A/C suction line - partially restricted or plugged.
    Erratic Operation or Compressor Not Running Ambient Air Temperature (AAT) sensor - poor connection
    A/C pressure transducer - poor connection
    Evaporator temperature sensor - poor connection
    Low refrigerant charge - leak in system
    Additional Possible Components or Causes Associated With Inadequate Compressor Operation 
    Compressor Drive Belt - loose
    Compressor Clutch - slipping
    Clutch Coil Open - shorted, or loose mounting
    Control assembly switch - dirty contacts or sticking open
    Clutch Wiring Circuit - high resistance, open or blown fuse
    Compressor operation interrupted by engine computer
    Low refrigerant charge - leak in system
    Additional Possible Components or Causes Associated With a Damaged Compressor 
    Incorrect Clutch Air-gap
    Suction accumulator - refrigerant oil bleed hose plugged
    Refrigerant Leaks
    (1) Low pressure reading will be normal to high if restriction is downstream of service access valve.
    (2) Low pressure reading will be low restriction is upstream of service access valve.
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