A/C Performance Test

Now that springtime is here, hot summer weather cannot be far behind. And even if you live in a climate where you do not experience winter, you know that much warmer temperatures are lurking in the shadows. With this in mind, this time of year is a good time to check the operation of the A/C system in your customers’ vehicles. And if you are running A/C system check specials, this article is timely because the topic is diagnosing A/C system leaks.

A/C PERFORMANCE TEST

A/C leaks can be detected by the naked eye. However, there isn’t any smoke, steam or a stream of liquid that might be seen with a leaking water pump or a punctured radiator hose. The A/C system refrigerant is colorless and odorless. So, how do you know if the system is leaking?

The best way to determine if there is a possible leak is to know if the A/C system is not operating properly. This is done in one of two ways. First, your customer brings the vehicle to your facility and tells you that warm air, instead of cold air, is blowing out of the dashboard vents. Secondly, you do the performance test for your customer as part of a regular maintenance program in the early spring. As the result of either scenario, you now know if the A/C system is working correctly.

Remember, an A/C system that is not working properly doesn’t mean that there is a system leak. Other conditions, such as a bad compressor or a kinked refrigerant line can also result in poor system performance. But, system leaks are a common cause of poor system performance. Checking for refrigerant leaks should be at the top of your list when it is determined that the A/C system is not working right.

Let’s review the basics of the A/C performance test. First, a word of caution is necessary. The use of an A/C recycling/charging station for the purpose of determining the actual charge level of the system is not recommended. These stations do not reflect the correct amount of refrigerant charge after a single reclaim cycle.

Check for any Diagnostic Trouble Codes (DTCs). If none are found in the Powertrain Control Module (PCM) or Engine Control Module (ECM), go to the next step.

Connect a tachometer and manifold gauge set. Be sure that the ambient air where the vehicle is being tested is at least 70°F. Also, the evaporator temperature sensor must be a minimum of 65°F. Place the vehicle in the testing area and let the temperature within the vehicle reach at least 65°F.

Operate the heating-A/C system under the following conditions:
1. Engine at normal operating temperature
2. Engine at normal idle speed
3. Doors and windows closed
4. Transaxle or transmission in Park
5. Heater-A/C controls set to Recirculation mode, full cool, panel mode, the blower on High and the A/C compressor engaged; if the compressor does not engage, the A/C system problem is not due to a refrigerant leak; you can stop the test here and focus on correcting the compressor problem
6. All panel outlet vanes are open and positioned straight ahead

Insert a thermometer in the driver side center panel air outlet; operate the A/C system for at least 5 minutes. With the compressor engaged, compare the air temperature at the center panel outlet and compressor discharge pressure to the appropriate performance chart. If the air outlet temperature fails to meet specifications, we have a problem.

DIAGNOSING AND FINDING A LEAK

While there are many possible causes for poor A/C system performance, we are going to concentrate on the refrigerant and possible refrigerant leaks. The refrigerant lines and hoses carry the refrigerant between the various system components. The O-rings at the connection points for the lines and hoses are a common location of refrigerant leaks.

If the A/C system is not cooling properly, determine if the system is fully charged. If the refrigerant system is low or empty, a leak at a refrigerant line, connector fitting, component or component seal is likely. Figure 1 shows the condenser connections, which are possible locations of refrigerant leaks. The discharge line connection is shown, in exploded view, in Figure 2. This is another source of a refrigerant leak.

To check for a refrigerant leak, look for an oily residue on, or near, the refrigerant lines, connection fittings, components and component seals, including those shown in the two illustrations. If such a residue is seen, that is a good indication that a refrigerant leak is present. The exact leak location should be confirmed with an electronic leak detector before repairing or replacing the component.

Such a detector, designed for R-134a, is highly recommended for locating and confirming system leaks. Follow the operating instructions supplied by the detector manufacturer for proper care and use of this equipment.

To further expand our leak detection efforts, perform the following test procedures for the system empty and the system low.

For the system empty, evacuate the refrigerant system to the lowest degree of vacuum possible (approximately 28 in Hg). Determine if the system can hold a vacuum for 15 minutes. If the vacuum is held for this length of time, a leak is probably not present. If the system will not maintain this vacuum level, continue the test. Prepare and dispense 10 ounces of refrigerant into the evacuated system, then proceed to the system low test.

Position the vehicle in a wind free work area. This will aid in detecting small leaks. Operate the heating-A/C system with the engine at idle under the following conditions for at least 5 minutes:
1. Doors or windows open
2. Transaxle in Park
3. Heater-A/C controls set to outside air, full cool, panel mode, high blower and with the A/C compressor engaged
4. If equipped with rear heater-A/C system, such as in a minivan, set the rear controls to full cool and high blower

Note: Remember, a leak detector designed for R-12 refrigerant will not detect leaks in an R-134a refrigerant system.

Shut the vehicle off and wait 2 to 7 minutes. Then, use the electronic leak detector that is designed for R-134a refrigerant and search for leaks. Fittings, lines or components that appear oily usually indicate, as mentioned above, a refrigerant leak.

To inspect the A/C evaporator for leaks, insert the leak detector probe into the drain tube opening or air outlet. A special dye for R-134a is also available to aid in leak detection.