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Diagnostic Table

    NOTE: The following table is used to guide diagnosis of the refrigerant system if operating pressures are outside normal limits.
  1. Proceed to the diagnostic table.
DIAGNOSTIC TABLE

High (Discharge) Pressure Low (Suction) Pressure Component- Causes
High or clutch cycling High Condenser - inadequate airflow.
High Normal to high Engine - overheating.
Normal to high Normal Refrigerant overcharge - air in refrigerant.
Normal to low High Fixed orifice tube - missing O-rings leaking/missing.
Normal to low Normal to high A/C suction line - partially restricted or plugged (1).
Normal to low Low or clutch cycling Low refrigerant charge, A/C suction line - partially restricted or plugged (2) A/C cycling switch - sticking closed.
Erratic operation or compressor not running A/C cycling switch - poor connection at A/C clutch connector or clutch cycling switch connector. A/C electrical circuit erratic - see A/C Electrical Circuit Wiring Diagram in SYSTEM WIRING DIAGRAMS .
Normal to low High Compressor - low performance.
Additional Possible Cause Components 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
Additional Possible Cause Components 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 pressure is taken at accumulator and if restriction is downstream of service access valve.

(2) Low pressure reading will be low if pressure is taken near the compressor and restriction is upstream of service access valve.
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