How To Attach An Air Conditioning Manifold Gauge And Perform Basic Refrigerant Pressure Readings

If you suspect your home's central air conditioning system isn't operating properly, you can tell a lot simply by measuring the system's refrigerant pressures. It may seem intimidating to perform your own system pressure tests, but it is actually quite straightforward to do so. Below is how to measure your central air conditioning system's pressures to help know whether or not you should contact a technician for servicing:

The equipment needed

Measuring the system's pressure requires a few tools and pieces of equipment. Below is what you need:

  • Air conditioning manifold gauge – a basic air conditioning gauge actually consists of two related, but separate, gauges. In addition, three hoses—red, blue and yellow in color—lead to the gauge manifold that joins both gauges and their hand-valves. You will not need to use the yellow hose for measuring your system pressure. Most gauges are designed to be used with systems containing different types of refrigerants (e.g., R-22), so be sure to know which scale is appropriate for your system when referencing the gauges.

  • Charging chart – this is a visual reference that provides detailed data about normal system pressures within both the suction and high-pressure lines. This information is available in the manufacturer's service manual for your particular system model.

  • Outdoor thermometer

  • Adjustable wrench

The measurement procedure

1. Turn off the main power switch for the system – most central air conditioning systems have an outdoor main power switch located near the outside unit; be sure to turn off the power to the system to prevent electrical accidents or damage to the system.

2. Locate your system's gauge connection valves – central air conditioning systems contain two refrigerant lines connected to the outside units that house the condensers and compressors. The larger diameter line is the suction line that returns gaseous refrigerants to the condenser. The smaller diameter line is the high-pressure line, which is sometimes called the liquid line. At the point where the lines enter the outside unit, look closely and you will see valves that are most likely capped shut. These valves are for the purpose of monitoring refrigerant pressures, both suction and high-pressure.

3. Remove the connection valve caps – with a small adjustable wrench, remove the valve caps from the suction line and high-pressure line. Set the caps aside in a safe location.

4. Attach the manifold gauge to the valves – once you remove the valve caps, you can attach the manifold pressure gauge to the suction and high-pressure lines. Be sure the red hose leads to the high-pressure line valve and match the blue hose with the suction line connection. Many valves use a Shrader valve design that is similar to an automotive tire valve; this simplifies matters by allowing you to screw the gauge hoses to the appropriate line valve fitting. When you initially screw the gauge hoses on to the valves, a tiny release of refrigerant is normal, but avoid making careless, wasteful releases when using them.

5. Take your pressure readings – once the hoses are firmly connected to the suction and high-pressure line valves, turn on the air conditioner main power switch so the compressor will also begin pumping. Next, take a look at both gauges, and note the readings in pounds-per-square-inch (PSI) you see on the scales that match your system's refrigerant type. Write down these readings, and cross-reference them with the current outdoor temperature on your charging chart. 'the charging chart will provide you with an indication whether your readings are too high or too low.

6. Disconnect the gauge – once you have obtained the information needed, turn off the main power switch again to shut down the system. Disconnect the gauge from the valves on the suction and high-pressure lines, and screw the valve caps back on to protect the valves from damage.

7. Interpreting the results – if your pressure readings are abnormal, contact an air conditioner contractor. who can assist you with further diagnosis and recharging your system, if necessary. Only an EPA-certified technician may legally recharge a system with refrigerant, so be sure not to attempt it yourself.