Flushing can help clean blockages by dislodging sludge and debris and purging it from the system. There are several ways to flush an A/C system. One method is to use a plastic bottle to insert the approved solvent into the system. Then, blow it through using dry air or nitrogen from a rubber-tipped blow gun at about 100 psi. Only flush the solvent through heat exchangers and free-flowing hoses. Always flush in the reverse direction of refrigerant flow to dislodge any material caught inside. After the system is flushed completely, blow each component dry in both directions. When sludge or debris is found in an A/C system, the orifice tube or expansion valve, accumulator, and condenser should always be replaced.

Testing the refrigerant system for leaks is one of the most important tasks when troubleshooting automotive A/C systems. Keep in mind that it's common for systems that are in good condition to lose a small amount of refrigerant each year; this is considered normal.

When looking for leaks, a good visual inspection of the entire A/C system is a great first step. The system contains the oil necessary to lubricate the compressor. The presence of an oily film around fittings, lines, the compressor, or any components is a strong indication of a refrigerant leak. Most leaks are small and allow refrigerant to escape over long periods of time, so they may be hard to detect with a visual inspection. There are several methods you can use to detect these small leaks.

The first is an electronic leak detector, which can be used with all types of refrigerants. This is a handheld, battery-operated unit that electronically "sniffs" for leaks. Refrigerant is heavier than air, so you'll need to run the leak detector's test probes directly below any suspected leak areas, including all fittings, lines, and components. Try to avoid getting oil or residue on the end of the leak sniffer, as this can give you a false reading.

Some of the more common sources of leaks are service-port Schrader valves, compressor front seals, compressor center seals, and evaporators. When checking the evaporator, you can insert the electronic leak detector's probe into the evaporator drain. Most detectors have an alarm that will go off when it detects the presence of refrigerant. Some detector models may have flashing lights or a buzzer to alert you when they detect refrigerant.

The method of leak detection preferred by most automotive technicians involves a fluorescent dye (Image E). To find refrigerant leaks using the fluorescent tracer system, the fluorescent dye must be installed into the vehicle's A/C system. There are several ways this can be accomplished, with two methods being the most common. The first uses an adaptor that can be placed on the yellow hose of your gauge set; this allows the dye to be installed when charging the system. Another method is to use a pressurized can that contains dye and install it through the low-side filling port.

With the dye installed, run the A/C system for several minutes to distribute the dye evenly. Then, use yellow, UV-enhancing glasses and a black light to examine the system. If there are any leaks present, the fluorescent dye will show up easily using the light and UV glasses (Image F).

Once you've found your leak and are ready to replace the faulty component—a process that requires the removal of the old refrigerant—you'll need to have that refrigerant reclaimed and the new refrigerant added by a certified A/C-repair shop. Federal law prohibits the venting of any type of refrigerant into the atmosphere, and this law is enforced with a steep fine or even imprisonment.

Vehicles should only be recharged with the same refrigerant that is already in the system, unless an older system is being retrofitted. When two different refrigerants are intermixed, it changes the operating pressure and cooling properties of both. There are a number of EPA-approved refrigerant products that can be used in place of R-12 in older-vehicle retrofits. R-134a replacement refrigerant has been on the market for a long time and has proven to be reliable. Keep in mind that when you change refrigerants, you must install a compressor oil that is compatible with your new refrigerant. The R-12 system uses a mineral oil, while the R-134a requires POE or PAG oil when it is retrofitted (Image G).

After the repair is performed, the air and moisture will need to be removed. For this you'll need to evacuate the A/C system. This requires putting the system into a vacuum for approximately 20 minutes, which allows any moisture in the system to be boiled out. Remember from chemistry class that water will boil in a vacuum. This is an important step that requires specialized equipment.

This month we focused on the questions we most often receive about A/C gauges and basic system operation. Next month we'll provide you with detailed troubleshooting diagnostics using the A/C-gauge set and other methods, and explain how refrigerant flows through the system. Until then, good luck and stay cool.