Caution: 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.

Important: Vehicles equipped with an early warning system for low refrigerant may set low refrigerant codes.

Perform a refrigerant leak test on the system whenever a leak is suspected. Suspect leakage when a system indication of a low charge occurs or after any service operation which disturbs the following items:

Tools Required

The halogen leak detector is the most useful tool in locating refrigerant leaks. TheJ 39400 is a small unit that operates on 12 V DC. The J 39400 provides an audible signal. The signal increases in frequency when R-12 or R-134a is detected. There are three settings:

Use the gross leak setting for isolating very large leaks already found in one of the other two settings.

Ensure that the instrument is correctly calibrated according the instrument's instructions. Ensure that the detector is set correctly for the type of refrigerant system being tested.

Before you begin the test, ensure that the refrigerant system is sufficiently charged for leak testing by measuring the static pressure with a gage set. Readings in the range 413 to 689 kPa (60 to 100 psig) are acceptable to conduct a leak test.

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

A small piece of lint from cotton gloves or shop cloths can create a leak path across an O-ring.

The successful use of this and any other electronic leak detector depends on the scan rate. It also depends on carefully following the manufacturer's instructions regarding the following items:

Completely circle each joint. Move the leak detector at a rate of 1-2 inches per second with the tip of the probe as close to the surface as possible. Ensure that the tip of the probe is no more than 0.8 cm (0.25 in) from the surface and does not block air intake.

A leak is indicated when the audible tone goes from a steady 1-2 clicks per second to a solid alarm. Adjust the balance knob frequently in order to maintain the 1-2 clicks per second rate.

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

Important: Always follow the refrigerant system around in a continuous path. Do not miss any areas of potential leaks. Test all of the areas in order to ensure that the entire system is leak free, even when a leak was already found.

Clean all of the surfaces in order to prevent a false warning. Ensure that all surfaces are dry since ingestion of liquids will damage the detector. The following items may be tested using this procedure:

Tools Required

R-134a refrigerant is uniquely different from the R-12 refrigerant that was used in the past. R-134a may require additional methods to detect leaks. The R-134a molecule is smaller than the R-12 molecule and can leak through smaller openings. Also, R-134a does not contain chlorine, which the electronic leak detectors found easy to identify. The tracer dye method is meant to be used in conjunction with the electronic leak detector. The tracer dye method will pinpoint smaller leaks that would not be detected by using the electronic leak detector alone. R-134a tracer dye requires time. Depending upon the rate of leak, it may take up to 7 days for the leak to become visible.

Important: 

Liquid/bubbles leak detectors have very limited usefulness. This is due to the restricted visibility in refrigerant systems and the lack of sensitivity in liquid/bubbles leak detectors.

The primary seal for the service ports is the sealing cap. This cap contains a specially designed O-ring or gasket which provides a leak-free seal. Loss of refrigerant charge will occur in the following situations:

One of the most difficult leaks to find is in the evaporator core. Follow the instructions below in order to lead test the core:

1. Turn the blower fan on high for 15 or more seconds.
2. Shut the blower fan off.
3. Wait 10 minutes.
4. Remove the blower fan power module or resistor block if accessible.
5. If the blower fan power module is not accessible, inspect the condenser drain tube for moisture.
6. If the condenser drain tube is dry, use the drain tube.
7. Insert the leak detector probe into the resistor/relay opening, or the blower case drain tube. If the detector goes to a solid alarm, a leak has been found.
8. Inspect the core face for evidence of refrigerant oil with a flashlight. On R-134a systems, the lubricant is water soluble so no evidence of oil is likely, even with a leak.

1. Blow shop air behind and in front of the compressor clutch/pulley for at least 15 seconds.
2. Wait for 1-2 minutes.
3. Probe the area in front of the pulley. If the detector goes to a solid alarm, a leak has been found.