Temperature Compensated Pressure Test

A temperature compensated pressure test for refrigerant piping is critical to confirm that no piping leakage exists. While nitrogen is inert (it does not create an oxidative reaction), it does follow the gas laws. If the ambient temperature changes, so does the resulting pressure. For more detail, read this article at HVAC School.

Preparation

Before testing, sweep the system from the high side backward to the low side to carry out any air. A continual sweep of nitrogen with a purge/pressure testing regulator is recommended. Removing air before testing is critical: if air remains in the pressurized system, moisture can fall out as liquid, making it very hard to remove during evacuation.

Running the Test

Use the liquid line temperature and high pressure to complete the test. Pressurize the system to the maximum rated test pressure of the lowest-rated component. (For example, an evaporator may say "Max test pressure 250 psi.")

Sweep the system, bring it to the test pressure, and allow 5 to 10 minutes to stabilize. Then start the temperature compensated pressure test. The initial pressure, temperature, and timestamp will be captured. Allow the test to run for at least 600 seconds (10 minutes), or longer if required by the manufacturer.

When the test ends, the final temperature and pressure are captured and measureQuick produces a pass/fail result based on the gas law calculations.

If you are a Premier Services subscriber, you can add the test results to your measureQuick report in place of the geolocation map.

Tools Needed

• One psychrometer for outdoor air temperature
• One pipe temperature clamp for the liquid line
• One pressure probe for high pressure

For correct probe and clamp positioning, see Proper Wireless Probe Placement. For testing without gauges attached, see Introduction to Non-Invasive System Testing.