A quality leak detector will find most leaks, but there are some they won't find. To make sure I find them all, I like to use a UV dye. Bob Savasta, marketing communications manager with Tracer Products ( http://www.tracerproducts.com/), offers a few tips on dyes.

First, check to see if the manufacturer already has added dye to the system you are testing. Many do, in the form of a wafer in the accumulator or receiver-drier. (OEM replacement components for these vehicles may also contain this wafer, making the addition of aftermarket dye unnecessary.)

3 The yellow glasses aid in seeing the UV dye trace.

Depending on the size of the leak, dye may not reveal itself for 24 hours. (Some factory service bulletins say the "wafer" dye can take up to two weeks to completely circulate through the system.)

If there is no dye in the system, I generally add the specified amount during my repair. I tell the customer that there still might be a small leak in the system, and ask them to return in a week or so for a free recheck. It's better to tell them up front and have no problem than to have them come back with a complaint.

Time To Charge It Up

Proper system charging is critical to the operation and health of the A/C system. Too little, and cooling efficiency and system lubrication suffer. Too much, and compressor head pressures and temperatures increase. Both conditions will lead to a short life for the compressor.

4 A light tap or two can get a weak relay to reveal itself.

Enter SAE standard J2788, the new standard for RRR equipment. Equipment certified to this standard must recover 95 percent of the total system charge in less than 30 minutes. Measure that recovered charge to within 1 ounce, and recharge the system to within 0.50 ounce. Only a few machines currently meet these standards. While you can still buy equipment certified to the old standard (either new stock that hasn't been sold yet or used equipment), consider replacing your RRR equipment with a J2788-compliant machine when the time comes. With some models also offering options like built-in identifiers and the capability to perform refrigerant flushes, in the long run these machines will make you money.

Handling Those Intermittent Complaints

Intermittent complaints always can be a challenge, but when you've seen as many as Glenn Farrell of Farrell's Auto Air Conditioning in Kenner, La., has over the last 40 years, you come up with ways to win more than you lose. According to Farrell, the majority of these complaints can be traced to one of four possibilities: a faulty compressor relay, a pressure switch fault, a weak compressor clutch or a blend door fault. To test for the cause of an intermittent loss of cooling, first verify the overall health of the system using your normal testing methods. Correct any fault you find. If the system pressures and duct temperatures are OK, it's time to use a little patience and get the failure to show itself.

Warm up the engine. Set the HVAC controls for Max A/C, blower speed on minimum, close the recirculation mode door and idle the engine at 1,500 rpm. At these settings, the compressor should cycle as often as possible. Monitor the duct temperature in the center duct and vary the temperature setting from full cold to full hot several times to check the operation of the mode door.

Return the controls to the original settings and watch the duct temperature. As soon as you see it start to warm up, see if the compressor clutch is engaged. If so, take another look at that blend door. If not engaged, lightly tap or bypass the relay and/or pressure switch to see if the compressor clutch engages. If still no engagement, lightly and carefully tap on the clutch face itself. If the clutch now engages, you've found the fault. (An alternative to tapping on the clutch face is to verify power and ground to the coil with the clutch disengaged. If that's OK, odds are it's in the coil or clutch facing itself.)

Pete Meier is an ASE CMAT, a member of iATN, and a full-time tech with CarMax in Tampa, Fla. He started doing oil changes and minor repairs more than 30 years ago and brings a variety of experience to bear. His current job involves all manufacturers' lines, and, as Pete says, "provides me constant opportunity to learn something new." Diagnosing electrical and drivability problems are his favorite challenges.