Metro, Prizm 2000-2002

Testing The System


Leak Testing

Only a MVAC-trained, EPA-certified, automotive technician should service the A/C system or its components.

Refer to the precautions outlined earlier in this section before any leak testing procedures are performed.

Before beginning the leak test, ensure that the refrigerant system has a sufficient charge. Measure the static pressure by using a gauge set. The system must have a pressure above 345 kPa (50 psi) for an acceptable leak test.

Most leaks occur at the refrigerant fittings or at the connections. Leaks may result from incorrect torque, damaged O-rings, lack of lubricant to the O-rings or dirt/debris across an O-ring.

The smallest piece of lint from cotton gloves or shop cloths may create a leak path along an O-ring.

Compressor And Block Fitting

A worn shaft seal often causes compressor gas leaks. A small amount of compressor oil leakage from the shaft seal is normal. Replace the compressor only when a large leak is detected. At times, an oil leak can be detected visually. A gas leak check will require a gas leak detector.

  1. For at least 15 seconds, blow shop air behind the compressor clutch pulley and in front of the compressor clutch pulley.
  3. Probe the compressor area. If the detector goes to a solid alarm, a leak is present.

Electronic Leak Detection

Do not operate the detector in a combustible atmosphere since its sensor operates at high temperature. Personal injury or damage to the equipment may result.

Use the J-39400 Halogen Leak Detector in order to locate refrigerant leaks. The J-39400 provides an audible signal that increases in frequency if the unit detects refrigerant.

Use the gross leak setting on the detector to isolate very large leaks that you found by using another setting. Correctly calibrate the instrument according to the instructions. Set the detector to the refrigerant setting that is correct for the system being tested. Place the detector GAS switch in the R-134a setting prior to use.

The successful use of an electronic leak detector depends greatly upon the scan rate and correct calibration, operation, and maintenance of the detector, according to the manufacturer's instructions.

Halogen leak detectors are sensitive to windshield washer solutions, solvents and cleaners and some adhesives.

Follow the refrigerant system in a continuous path in order to ensure that you do not miss any areas of potential leaks. Verify that all areas of the system are leak-free, even if you already found one leak.

  1. Verify that the surfaces are clean in order to prevent a false warning.
  3. Verify that the surfaces are dry, because the ingestion of liquids damages the detector.
  5. Blow out the engine compartment using an air hose prior to the test. The presence of vapors may cause a false warning.
  7. Move the probe completely around each joint.
  9. Move the probe at a rate of 25-50mm (1-2 in) per second.
  11. Keep the tip on the probe as close to the surface as possible. Keep the tip closer than 6mm (1/4 in) from the surface. Do not block the air intake of the probe.
  13. Adjust the balance knob frequently in order to maintain the 1-2 clicks per second rate. If the steady 1-2 clicks per second changes to a solid alarm, a leak is present.
  15. Test the following areas:
    1. The pressure sensor
    3. The receiver-dryer inlet
    5. The receiver-dryer outlet
    7. The evaporator inlet
    9. The evaporator outlet
    11. The condenser inlet
    13. The condenser outlet
    15. The compressor inlet
    17. The compressor outlet
    19. Other connections
    21. All the brazed areas
    23. All the welded areas
    25. Areas that show signs of damage
    27. Hose couplings
    29. The compressor rear head and the housing joints


Evaporator Core

Leaks in the evaporator core are difficult to find. The core is inside an encapsulated module. The core is inaccessible to leak detector devices. Use the following procedure in order to test the core:

  1. Turn the blower fan on HIGH for 15 seconds. Shut the fan off.
  3. Wait 10 minutes.
  5. Remove the blower motor or the blower motor resistor.
  7. Insert the leak detector probe into the opening. Get the probe as close as possible to the evaporator. A solid alarm on the detector indicates a leak
  9. If possible, use a flashlight in order to visually inspect the core face for evidence of refrigerant oil.

Fluorescent Dye Leak Detection

Tools Required:

J-41447 Fluorescent Tracer Dye
J-41459 R134a A/C Tracer Dye Injector
J-28428-E High Intensity Black Light

The tracer dye J 41447 was developed for use with the A/C Refrigerant 134a (R-134a) equipped vehicles or with vehicles that have been retrofitted from R-12 to R-134a. Do not use any other tracer dye in the R-134a system. Use of another dye may affect the system reliability and cause premature compressor failure. Use only a 1/4 oz. charge of the dye. Larger amounts may compromise the reliability of the A/C system. After adding the tracer dye, clean the service valves and all affected surfaces of the dye with GM Engine Degreaser GM P/N 1050436 or an equivalent in order to prevent a false diagnosis.

The R-134a refrigerant is different from the R-12 refrigerant that was used in the past. The R-134a refrigerant may require additional methods for leak detection.

The R-134a molecule is smaller than the R-12 molecule and can leak through smaller openings.

The fluorescent leak detection method will locate smaller leaks.

The R-134a dye takes time to work through the A/C system. Depending on the rate of the leak, the dye may not be visible for 7 days.

The dye mixed with PAG oil remains detectable in the system for 2 years. Larger amounts may compromise the reliability of the system. Use only the 1/4-oz charge of dye.

If you inspect the leak locations with an ultraviolet light, the dye glows yellow and green.

PAG oil is soluble in water. Condensation on the refrigeration lines, or on the evaporator core, may wash the dye off the lines, or off the core. This may make some leaks harder to locate.

Fluorescent dye at the evaporator core drain indicates a core leak.

Service Access Ports

The main seal for the service port is the sealing cap. This cap contains a special O-ring or a gasket that provides a leak-free seal. A loose, missing, or incorrect cap may cause a loss of refrigerant.