Last month we discussed air-conditioning troubleshooting and how you can diagnose many of these problems yourself, including:
&bull What tools are needed for diagnosing your A/C system
&bull How to hook up your A/C gauges
&bull Static pressure and what it means
&bull Normal running pressures
&bull The importance of having your system charged with the correct amount of refrigerant for proper performance
&bull The differences in gauge readings between R-12 and R134a
&bull Different leak detectors and how they should be used
&bull How to flush your A/C system
&bull The differences in compressor oils
&bull The need to have the old refrigerant reclaimed and the new refrigerant added by a certified A/C-repair shop
This month we will provide you with detailed troubleshooting diagnostics using the A/C-gauge set. This will help you to understand the role pressure plays in different parts of the system. Don't forget to wear safety equipment and protective eye wear. Remember: refrigerant can be under high pressure and is therefore potentially dangerous.
Gauge Readings: low side—60 to 90 psi, high side—60 to 90 psi
With the vehicle off, the gauges should read the same or be extremely close on both the low-pressure and high-pressure sides (see lead photo). This indicates that both sides are equalized. Static pressure is an indicator that there is some refrigerant in the system and that you can proceed with the A/C-performance test.
Temperature plays a big role in static pressure readings. The higher the ambient temperature, the higher the static pressure will read. If static pressures are under 50 psi, you can deduce that the system is low, and that it will need to be recharged before proceeding with performance testing or diagnostics.
Assuming that's the case, you'll first need to recover the remaining refrigerant from the system. Put the system into a vacuum for approximately 20 minutes; this allows any existing moisture to be boiled out. Then recharge the system with the factory-specified amount of refrigerant (usually found on a label somewhere inside the engine compartment). Any oil that was lost should be re-added during the recharge process. Finally, check the A/C system's operation and performance.
While the system is being evacuated, it's a good idea to perform a visual inspection. The A/C system contains 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. As a result, they may be hard to detect with a visual inspection and may instead require the use of a leak-detection device after the system has been recharged.