• SkillCat Team

Standing Pressure Test

Updated: Feb 24

EPA 608 Core Chapter 39 (Take full course for free)


In this module, we will discuss various procedures and techniques that need to be followed while performing the standing pressure test.


1. Overview


As we mentioned, the standing pressure test is when we pressurize the system and then use electronic leak detection to identify the leak.


When we are pressurizing equipment, we want to make sure that we do not exceed the low side test pressure for the equipment.


The test pressure for equipment can be found on the equipment’s nameplate. Make sure you do not exceed the low side test pressure indicated on the nameplate.


We pressurize the system by adding a pressurized gas.


Our options are

  1. Dry nitrogen, and

  2. A mixture of dry nitrogen and a refrigerant gas

  3. For example: Dry nitrogen with R-22 refrigerant


When we mix R-22 with nitrogen to do leak testing, this is called a trace gas. Trace gases are not considered refrigerants under EPA refrigerant management guidelines.



2. Nitrogen


Note that only specific refrigerants can be used for this method. For example, R-22 can be mixed with dry nitrogen to leak check a system. But R-12 cannot be mixed with dry nitrogen for this method.


Before pressurizing the system, we need to start by evacuating the system. We need to first recover the system to 15 psig.


Technicians cannot add nitrogen to a fully charged system. This would contaminate the refrigerant in the system because you would be combining two substances together.


The resulting mix cannot be separated. Imagine adding orange juice to milk. You cannot separate the two liquids after mixing. This is why you cannot add nitrogen to a fully charged system.


By recovering the system to 15 psig, you are leaving some refrigerant in the system. Recall that electronic leak detectors detect leaks by sensing refrigerant in the general area. There has to be refrigerant leaking in order to locate where the leak is.


After pressurizing the system, we locate the leak with the electronic leak detector. Then we have to recover the nitrogen and refrigerant mixture in a separate tank.


If we use the same tank as the one used to contain nitrogen or the refrigerant, it would “cross-contaminate” the tanks. There would be residue left in the tank. If the tank were to be used for nitrogen, you would have the residue of refrigerant. So we need to recover in a separate tank.


The EPA allows technicians to mix R-22 and dry nitrogen to detect leaks. But as we said, once you have a mixture, you cannot use that mixture anywhere else. You also have to recover the mixture in a separate recovery cylinder.



3. Flammable Refrigerant Procedures


When leak testing a system containing flammable refrigerants such as hydrocarbons (propane, isobutane) or HFOs, we must always install a filter-drier. A filter-drier removes the moisture and contaminants from the refrigerant.

We must also perform a standing pressure test for systems with flammable refrigerants.


For a system containing 50 pounds or more of a refrigerant and with triggered leak rates, two verification tests should be performed. One is done before charging the system and one after the system is working normally.


We will look into the details of the acceptable leak rates for different systems in the courses for Types I, II, and III.



4. Conclusion


In this module, we discussed what procedures to follow while performing the standing pressure test.

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