Handling the pressure

Jan. 1, 2020
For many, the first days of spring mark the beginning of a new A/C service season. For those of us living in the South, A/C service is a year-round business. If we can diagnose A/C problems more efficiently, service them properly and reduce the chanc

There are a number of tips and techniques to help make your air-conditioning season more profitable.

For many, the first days of spring mark the beginning of a new A/C service season. For those of us living in the South, A/C service is a year-round business. If we can diagnose A/C problems more efficiently, service them properly and reduce the chance of comebacks, we can add more dollars to the bottom line. Let's take a fresh look at routine A/C service and see if I can offer a few tips to help you accomplish these goals.

Before You Connect

Bob's A/C isn't cooling like he thinks it should. His buddy, Ima Fixeruper, tells him, "It just needs a little freon." Ima just happens to have ordered some online, and Bob's more than welcome to it. Oh yeah, he's also got this self-sealing stuff Bob can put in, just in case. Can't hurt, right?

A few months later, the car isn't cooling at all. Bob is now in your shop, but he isn't telling you he installed sealant and a blend refrigerant in his car. This certainly should make the case that you should use a refrigerant identifier on every car before you connect your shop's service equipment. They are available from simple units to high tech jobs; the choice is yours. Before you connect your service equipment, look for signs of sealant by visually inspecting both service ports. Take a sample and identify what's in the system. It will protect your equipment, your refrigerant supply and, most importantly, it will protect you.

Now That It's Safe

Once you've verified the system isn't contaminated, connect your service gauges and test the system's operation. I start with four basic measurements: low side pressure, high side pressure, ambient air temperature and center duct temperature. Operating pressures are affected by relative humidity and ambient air temperature at the condenser. Take this measurement a few inches in front of the condenser itself. If you've just moved the car from a hot parking lot into an air-conditioned shop (or the other way around), allow the system five to 10 minutes to adapt to the temperature change before taking your pressure readings.

Specifications for individual vehicles vary, and so do the testing methods used to obtain those readings. Use your service information system to see if these pressure specs should be taken with all the doors closed or open. Most are done with the system set to Max A/C and the blower set to high. This will impact the temperature differential between ambient air temperature and the temperature measured at the duct, and will help you spot a weak system.

Where Is The Leak?

Most loss-of-cooling complaints are caused by loss of refrigerant in the system. This may be a normal loss over an extended time or due to a worn seal or leaking component. The two most common methods for leak detection in use today are refrigerant leak detectors (sniffers) and ultraviolet (UV)dyes.

I spoke with Becky Firman-Wagner of INFICON, the makers of the TEK-Mate leak detector (www.inficonservicetools.com). Here are her tips for finding those pesky leaks.

  • Do not leak check with the engine running.
  • Do not clean the components with any type of solvent prior to testing. These vapors can cause false alarms with some types of leak detectors.
  • Move the test probe no more than 1 inch to 2 inches per second, and hold it no more than 1 BC4 inch from the surface.
  • Understand your leak detector's background compensation feature.
  • Refrigerant is heavier than air and drips or sinks out of leak points.
  • Verify the leak source by removing the probe and rescanning the area.
  • Fans, wind and other air currents may blow away the refrigerant while testing. If possible, test in a still environment.
  • Know how your detector behaves when the battery is low or when the sensor or filter needs replacing.

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 (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.)

Observe the recommendations of the dye manufacturer for the amount of dye to add to the system. Some aftermarket dyes have co-solvents in them, and excessive dye use might affect system lubrication.

Dye is not a substitute for the addition of proper lubricating oils, unless specifically packaged with that oil.

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.

Most RRR (recovery, recycling and recharging) equipment in use today has charge accuracies of ± 1 ounce to 2 ounces. Considering there are many systems with total capacities in the range of 11 ounces to 14 ounces, that's a potential variance of ± 15 percent. Evacuation of the system with this equipment typically removes 75 percent to 85 percent of the total system charge, which means the rest of that expensive R-134a ends up in the atmosphere.

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.

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