J 39400 Electronic Leak Detector

Caution: Do not operate the detector in a combustible atmosphere since its sensor operates at high temperatures or personal injury and/or damage to the equipment may result.

Important: Halogen leak detectors are sensitive to windshield washing solutions, many solvents, cleaners, and some adhesives used in the vehicle. Ensure that the surfaces are clean and dry in order to prevent a false warning. The ingestion of liquids will damage the detector.

Perform a refrigerant leak test when the following conditions exist:

Many methods and special tools are available for use in order to perform the refrigerant leak test. No matter which tool is used, carefully perform the test.

The electronic leak detector is the most useful tool in locating refrigerant leaks. The J 39400 Electronic Leak Detector is a small unit that operates on a 12V DC. This unit produces an audible signal that increases in frequency as R-134a is detected. Ensure that the instrument is properly calibrated according to the instructions. Ensure the detector is in the proper setting for the type of refrigerant being tested. Place the detector GAS switch in the R-134a setting prior to use.

The most common leaks are found at the refrigerant fittings or the connections. The following conditions may cause the leaks:

Even the smallest piece of lint from cotton gloves or shop cloths may create a leak path across an O-ring seal.

The successful use of this and any other electronic detector depends greatly upon the scan rate. Carefully follow the manufacturer's instructions regarding the following items:

Important: Always follow the refrigerant system around in a continuous path in order to avoid missing any areas of potential leaks. Always test all areas in order to ensure that the entire system is leak free, even when one leak is already found.

Circle each joint completely by moving at 25-51 mm (1-2 in) per second with the tip of the probe as close to the surface as possible. Circle the joint no more than 6 mm (0.25 in) away. Do not block the air intake. The audible tone will go from a steady 1-2 clicks per second to a solid alarm to indicate a leak. Frequently adjust the balance knob in order to maintain the 1-2 clicks per second rate.

Use this procedure in order to test the following components:

The primary seal for the service ports is the sealing cap. The cap contains a specially designed O-ring seal or gasket that provide a leak-free seal. A loss of refrigerant charge will result if the following conditions exist:

One of the most difficult leaks to find is in the air conditioning (A/C) evaporator core. Use the following procedure in order to leak test the core:

1. Turn the blower fan on high for 15 or more seconds.
2. Turn the blower fan off.
3. Wait for 10 minutes.
4. Remove the blower motor resistor.
5. Insert the leak detector probe as close to the A/C evaporator as possible. A leak is detected if the detector goes to a solid alarm.
6. If possible, visually inspect the core face with a flashlight for evidence of refrigerant oil.

1. Blow shop air behind and in front of the air conditioning (A/C) compressor clutch/pulley for at least 15 seconds.
2. Wait for 1-2 minutes.
3. Probe the area in front of the pulley.

A leak is detected if the detector goes to a solid alarm.

Tools Required

Use the following diagnostic procedure when an air conditioning (A/C) refrigerant leak cannot be found using a J 39400 leak detector.

1. Make a copy of Attachment 1 (Service Information Form).
2. Use the J 39500-B and record the necessary information.
3. Recover the existing R-134a refrigerant and record the refrigerant weight.
4. Add J 41447 or GM P/N 12346303, using the J 41459 .
5. Re-charge the system following the procedures in Section 1B of the Service Manual.

Important: R-134a florescent dye will remain in the lubricant for the life of the vehicle as long as the vehicle's A/C system has not been flushed. If no leaks are found, return the vehicle to the customer. Advise the customer of the dye in the system and that the system may need to be rechecked at a later date. Attach the Service Information Form to the Warranty Repair Order when completed.

6. Test the system for leaks using a high intensity black light or GM P/N 12377979.