OK you read my article on How to Recharge Your Air Conditioning System and it worked OK for a few days, now it is blowing warm air again. You have a leak in the system that you need to locate and fix. You can use the old-fashion method for locating the leak using a soap and water solution. You could even use a commercial, liquid leak detection solution, but an electronic leak detector works best. The old-fashioned methods fail when it comes to locating leaking compressor seals because there is no way of applying the solution on them. The electronic leak detectors will sniff out those leaking seals with ease. Electronic leak detectors are not cheap, but when you remember that time is money, they are well worth the investment.

Test Equipment That You Will Need

Air conditioning manifold gauge set for R134a

Electronic leak detector

Where To Look For Leaks

All auto air conditioning systems leak some refrigerant from between the compressor shaft and the shaft seals and from microscopic holes in the hoses. New systems in perfect working order lose 0.1 to 0.2 ounces of refrigerant a year from around shaft seals and from microscopic holes in hoses. Those leaks become increasingly greater as the system ages.

Leaks can develop in the evaporators or condenser. The condenser sets in front of the engine radiator. Flying road debris causes damage to the condensers. The evaporator located inside the vehicle and less easily damaged. A leak in the evaporator or the condenser core is two of the most expensive leaks to repair because it means replacing the evaporator or condenser.

Leaks can also develop in the accumulator, at tube and hose connections. Service fittings can develop leaks. In-line filters, orifice tubes, spring-lock couplings, and hoses are other sources of leaks.

Preparing to Trace A Leak

Bring the air conditioning system up to operating pressure before attempting to trace a leak. Add fresh refrigerant to bring the system to operating pressure if necessary. You will lose the added refrigerant during the repair.

A word of warning is in order here: if you have a vehicle air conditioner that uses Freon R12, do not attempt to service it yourself unless you are a certified/licensed air condition technician. Releasing R12 into the atmosphere not only damages the Ozone layer, it is a violation of environmental law and carries a stiff fine, take your vehicle to the professional for repair and retrofitting for using R134a, an environmentally friendly refrigerant.

Connect the Manifold Gauges to the System

1. Close the valves on the manifold gauges. Make sure that the "Yellow" hose is attached to one of the solid studs on the gauge set to block it off.
2. Attach the "Red" hose to the system's high-side service fitting.
3. Attach the "Blue" hose to the system's low-side service fitting.

Using The Manifold Gauges To Check System Pressure

1. Start the vehicle's engine and check to see that the air conditioner's compressor's clutch has engaged. Some systems have a low-pressure switch that will keep the clutch from engaging if the system pressure drops below a set point. If the clutch has not engaged, you need to bypass the cutout switch. Locate the clutch wire near the front of the compressor, and unplug it. Using a fused jumper wire, connect the clutch directly to the positive battery terminal. The clutch should engage and the compressor should start to run.
2. Open the valves on the manifold gauges. For a fully charged R134a system, the low-side gauge, the "Blue" gauge, will read between 25 and 40 psi and the high side gauge the "Red" gauge, will read between 225 and 250 psi.
3. If necessary, add R134a refrigerant to bring the system pressures up to these numbers. Read my article How to Recharge Your Air Conditioning System to find out how to add refrigerant to your system.

How to Use an Electronic Leak Detector

1. Read the instructions that came with your electronic leak detector because different detectors have a different setup procedure. The steps I am presenting here are general and apply to all detectors.
2. Turn on the leak detector. The unit will come on with its sensitivity set to mid range. Adjust the sensitivity higher if the leak is not detected at the default setting. Adjust the sensitivity lower if the leak cannot be isolated with the default setting.
3. Run the detectors probe slowly over the hoses and connections. When a leak is detected the detectors beeping will switch to a continuous tone, and the flashing LED will remain in an on state.
4. Adjust the detector sensitivity as necessary to pinpoint the leak. If you get a steady tone before you have pinpointed the leak, lower the sensitivity and activate the detectors reset control.
5. Be careful to not contaminate the probe by touching its tip to any of the parts that you are checking for leaks.
6. Proceed slowly, moving the probe 1 to 2 inches per second. Moving the probe faster will not allow enough response time for the detector to respond to a leak. You will have moved beyond the leak's location by the time that the detector indicates the presence of a leak.
7. To test an evaporator, turn the air conditioner to its maximum setting for at least 15 seconds, then turn it off and wait at least 10 minutes for the refrigerant to accumulate in the evaporator's case before testing.
8. Verify that you have found an actual leak by resetting the detector and re-testing the area of the suspected leak.

Once a repair is made, the system will have to be evacuated before recharging. Pulling a vacuum also verifies that you have found and repaired all the leaks in the system.

I will explain how to evacuate a system and I will explain how to use a vacuum to check for leaks in my next article in this series.