![]() Connect the quick release connectors to the service ports on the high and low side refrigerant hoses. Unscrew the protective port caps and store in a safe place. R-134a TEMPERATURE PRESSURE CHART FOR EXPANSION VALVE SYSTEM - ENGINE AND AC RUNNINGĦ0☏ Low side pressure 7-15 psi High side pressure 120-170 psiħ0☏ Low side pressure 7-15 psi High side pressure 150-250 psiġ10☏ Low side pressure 50.55 psi High side pressure 340.345 ps Step 2: Connect the gauges to your car’s AC ports R-134a TEMPERATURE PRESSURE CHART FOR ORIFICE TUBE SYSTEM - ENGINE AND AC RUNNINGĪmbient Temperature ☏/☌ Low-Pressure Gauge High-Pressure GaugeĦ5☏ Low side pressure 25-35 psi High side pressure 135-155 psiħ0☏ Low side pressure 35-40 psi High side pressure 145-160 psiħ5☏ Low side pressure 35-45 psi High side pressure 150-170 psiĨ0☏ Low side pressure 40-50 psi High side pressure 175-210 psiĨ5☏ Low side pressure 45-55 psi High side pressure 225-250 psiĩ0☏ Low side pressure 45-55 psi High side pressure 250-270 psiĩ5☏ Low side pressure 50.55 psi High side pressure 275.300 psiġ00☏ Low side pressure 50-55 psi High side pressure 315-325 psiġ05☏ Low side pressure 50-55 psi High side pressure 330-335 psiġ10☏ Low side pressure 50.55 psi High side pressure 340.345 psiĪmbient temp is the outside atmospheric temperature. See the pressure chart below to see what I mean. If you don’t know which system you have, you can misinterpret the low side readings right off the bat and think your system is undercharged. What is this so important? Because expansion valve systems usually show a lower suction side pressure than an orifice tube system. You must use a pressure temperature chart or be using diagnostic gauges Step 1: Find out what type of refrigerant metering device your car usesĬlick on the image above and find the type of refrigerant metering device your vehicle uses.For example, you might see a low high side pressure and determine the compressor is bad, when in fact, your vehicle is equipped with a variable displacement compressor. You must know the type of compressor in your vehicle.To find out what in your vehicle, click on the image to the right and find your vehicle. You must know the type of system in your vehicle - orifice tubeĬlick on the image to find which type of system is used on your vehicle.It must be the temperature of the air coming into your car’s condenser. Don’t go by the temperature from a news or weather service. ![]() Measure temperature about 1-ft in front of the grille. ![]() What you have to know about your system before using AC gauges You can’t recover refrigerant through the gauges to get down to the factory specified fill capacity.īut gauges can give you a rough idea of what might be going on with your system when it’s running. The same applies if your system is overcharged. In other words, if your system is low on charge, you can’t use your gauge set to add refrigerant to get to factory specified fill capacity. The ONLY way to know if your system is properly charged is to evacuate it and add new refrigerant with a scale. Let’s get this straight from the get-go, gauges can tell you if the system pressures are in a normal range, over-pressurized, or under-pressurized, but they CANNOT tell you if the system has the correct charge. What the AC gauges can tell you when the system is running If you add more refrigerant without removing the air, the system won’t cool properly.ģ-ounce partial charge at 70° shows the SAME pressure as a fully charged system That also means you most likely have air in the system. If the static pressure reading is below what’s listed on the chart, the system is low on refrigerant that’s caused by a leak. If the static pressure reading is close to the chart, then conduct a running pressure test. Refer the temperature pressure chart below to see what static pressure should be for the measured air temperature. Then measure the underhood air temperature. If they are about the same, the system has equalized and you can record the stating pressure reading. With the AC system off for at least 30 minutes, check the pressure readings on the high and low side gauges. For more information about conducting tests using temperature probes, see this post. You’ll also need temperature probes and a multimeter that accepts K-style fittings. You can’t really diagnose with just a low-pressure gauge from a DIY AC recharge kit. You’ll need a manifold gauge set if you want to properly diagnose your car AC with gauges. Repair Topics > Air Conditioning Symptoms and Repair > Gauges and Gauge Pressures > Diagnose car AC with gauges Diagnose car AC with gauges How to diagnose your car AC with gauges Using a manifold gauge set to diagnose car AC issues
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