LEMON Manuals: Even more car manuals for everyone: 1960-2025
Home >> Lincoln >> 2021 >> Aviator Base, AWD >> Repair and Diagnosis >> External Pages >> Different car >> Section 203 (Climate Control System - General Information) >> General Procedures >> Refrigerant System Tests
April 5, 2026: LEMON Manuals is launched! Read the announcement.

Refrigerant System Tests

WARNING: This page is about a different car, the 2019 Lincoln MKC. However, it is still accessible from the selected car via links, so may be relevant.

For information on Ford Color Coded Illustrations, refer to OEM COLOR CODING

Inspection 

NOTE: In order to perform an accurate test the vehicle ambient temperature must be 21 deg. C (70 deg. F) or above.
  1. NOTE: Procedure 1 -- Ambient Temperature between 21 deg. C (70 deg. F) and 38 deg. C (100 deg. F)

    Run the engine until it reaches normal operating temperature.

  2. Connect the air conditioning service unit to the refrigerant system.
  3. Set temperature to (lowest possible temp setting) with the dual function disabled (if equipped). Manually set blower on HI. If the vehicle has a fresh air/recirc button, set it to FRESH. If the vehicle has an Air Conditioning (A/C) switch or compressor on switch, set it to Air Conditioning (A/C) ON.
  4. Open all vehicle windows and leave the hood open for the test. Open the rear doors.
  5. Confirm the compressor is operating and the engine cooling fan(s) are operating or engaged. Allow the vehicle to idle until the suction (low-side) and discharge (high-side) pressures are stable or fluctuate in a range that repeats.
  6. Record the ambient (shop) temperature.
  7. Record the discharge pressure. If the pressure is fluctuating, record the average value.
  8. Determine if the discharge pressure falls within the normal operating limits using the

    Normal Refrigerant Discharge Pressures 21 - 38 deg. C (70 - 100 deg. F) Ambient (30 - 60% Relative Humidity)  chart below.

    GFD395458Courtesy of FORD MOTOR COMPANY
  9. Record the suction pressure. If the pressure is fluctuating, record the average value.
  10. Determine if the suction pressure falls within the normal operating limits using the

    Normal Refrigerant Suction Pressures 21 - 38 deg. C (70 - 100 deg. F) Ambient (30 - 60% Relative Humidity)  chart below.

    GFD395459Courtesy of FORD MOTOR COMPANY
  11. NOTE: Use the following table to guide diagnosis of the refrigerant system if operating pressures are outside normal limits.

    Refer to the chart below.

    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 Low refrigerant charge -- leak in system.
    A/C suction line -- partially restricted or plugged. (2)
    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
    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 if restriction is upstream of service access valve.

Inspection 

  1. NOTE: Procedure 2 -- Ambient Temperature Above 38 deg. C (100 deg. F)

    Run the engine until it reaches normal operating temperature.

  2. Connect the air conditioning service unit to the refrigerant system.
  3. Set temperature to (lowest possible temp setting) with the dual function disabled (if equipped). Manually set blower on HI. If the vehicle has a fresh air/recirc button, set it to FRESH. If the vehicle has an Air Conditioning (A/C) switch or compressor on switch, set it to Air Conditioning (A/C) ON.
  4. Open all vehicle windows and leave the hood open for the test. Open the rear hatch and/or rear doors (if equipped).
  5. Confirm the compressor is operating and the engine cooling fan(s) are operating or engaged. Allow the vehicle to idle until the suction (low-side) and discharge (high-side) pressures are stable or fluctuate in a range that repeats.
  6. Record the ambient (shop) temperature.
  7. Record the discharge pressure. If the pressure is fluctuating, record the average value.
  8. Determine if the discharge pressure falls within the normal operating limits using the

    Normal Refrigerant Discharge Pressures 38 - 49 deg. C (100 - 120 deg. F) Ambient (15 - 40% Relative Humidity)  chart below.

    GFD395460Courtesy of FORD MOTOR COMPANY
  9. Record the suction pressure. If the pressure is fluctuating, record the average value.
  10. Determine if the suction pressure falls within the normal operating limits using the

    Normal Refrigerant Suction Pressures 38 - 49 deg. C (100 - 120 deg. F) Ambient (15 - 40% Relative Humidity)  chart below.

    GFD395461Courtesy of FORD MOTOR COMPANY
  11. NOTE: Use the following table to guide diagnosis of the refrigerant system if operating pressures are outside normal limits.

    Refer to the chart below.

    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 Low refrigerant charge -- leak in system.
    A/C suction line -- partially restricted or plugged. (2)
    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
    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 if restriction is upstream of service access valve.
scientia non olet · About LEMON Manuals