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.

Perform a refrigerant leak test on the system whenever you suspect a leak. Also perform a refrigerant leak test after a service operation which disturbs any of the following items:

Ensure that the vehicle has at least 0.4536 kg (1 lb) of refrigerant in the refrigeration system in order to perform a leak test.

Important: Halogen leak detectors are sensitive to the following items:

Use this procedure to test the following components:

Important: Follow a continuous path in to ensure that you will not miss any possible leaks. Test all areas of the system for leaks.

This type of leak detector is the most useful tool to locate refrigerant leaks. The J 39400 is a small unit that operates on 12 volts DC. The J 39400 provides an audible signal that increases in frequency as the unit detects R-134a. Follow the instructions included with the unit to properly calibrate the instrument. Use the detector in the proper setting for the type of tested refrigerant. Set the detector gas switch to R-134a prior to use.

The most common leaks occur at the refrigerant fittings or connections. The leaks may be the result of any of the following conditions:

Maintain a proper scan rate in order to successfully use the J 39400 or any other electronic leak detector. Carefully follow the manufacturer's instructions regarding the following items:

To test for leaks, complete the following steps:

1. Completely circle each joint with the probe at a rate of at 51 mm (1-2 in) per second.
2. Place the tip of the probe as close as possible to the surface, but no more than 6 mm (0.25 in) away. Do not block the probe tip air intake.
3. A leak exists when the audible tone goes from a steady 1-2 clicks per second to a continuous alarm.
4. Frequently adjust the balance knob in order to maintain the rate of 1-2 clicks per second.

Tools Required

Important: 

If you know that the system has lost charge and you can not find a leak with the J 39400 , use a fluorescent leak tracer dye. This dye mixes with R-134a PAG oil. When you inspect the leak locations with an ultraviolet light, the dye glows yellow/green.

The dye package contains a refrigerant leak detection notice sticker. Complete the sticker information and place the sticker near the charge label.

Use one of the following methods to inject the R-134a dye:

1. With the A/C system charged, use the instructions provided with the new R-134a leak injection tool J 41436-1 .
2. With the A/C system discharged, add dye into the new replaced component assembly.

After servicing an A/C component with dye, clean any residual dye from the joint and the access port. Cleaning will prevent a false diagnosis later.

The primary seal for the service ports is a sealing cap. The cap contains an O-ring or gasket that provides a leak-free seal. The following conditions will cause a refrigerant loss:

One of the most difficult leaks to find is in the evaporator core. Complete the following steps in order to test the core for leaks:

1. Turn the blower on HI for 15 or more seconds. Turn the blower off.
2. Wait 10 minutes.
3. Remove the blower motor resister.
4. Insert the leak detector probe into the opening. Try to get as close to the evaporator as possible.
5. A solid alarm on the detector indicates a leak.

1. Blow compressed air into the following locations for at least 15 seconds:

•	Behind the compressor clutch/pulley

•	In front of the compressor clutch/pulley

2. Wait 1-2 minutes.
3. Probe the area in front of the pulley.
4. A solid alarm on the detector indicates a leak.