• SkillCat Team

Leak Detection

EPA 608 Type 2 Chapter 3 (Take full course for free)


This module walks through different methods to detect a leak in a refrigeration system. Skip to quiz!


1. General Indicators of Leak


Recall that leaking of a refrigeration system means that the refrigerant fluid leaks out of a system and into the atmosphere. If a leak is not fixed in time, it will result in all the refrigerant leaking out, and the system will not function.


While troubleshooting a faulty system, one can look for visual indicators to conclude a leak in the system.


Low refrigerant in a system due to leaks will lead to over-pressurizing the remaining refrigerant. It is because the system has to provide the same cooling effect but with a lower amount of refrigerant. Recall that increasing pressure will also increase the temperature of the refrigerant.


An increase in the temperature of the refrigerant in the system leads to high superheat in the system. Excessive superheat is an indicator of a leak in high-pressure systems having a capillary tube. Let us understand this slide a bit more.


Superheat is the difference between the actual temperature and the ideal refrigerant

temperature on the suction side. A technician can measure the actual temperature on the suction side of an appliance. Technicians can get the ideal temperature from the equipment’s nameplate.


A Capillary tube is a thin cylindrical copper tube, a type of metering device generally found in older systems. The TEV(Thermal Expansion Valve) is also a type of metering device that is relatively new, more sophisticated, and precise. Superheat is automatically maintained constant by the TEV.


To reiterate the whole concept:

  • Low refrigerant in the system will increase its temperature.

  • An increase in the temperature of the system leads to high superheat.

  • Excessive superheat is an indicator of a leak in a high-pressure system having a capillary tube


2. Hermetic System


A hermetic system refers to a system that has a hermetic compressor installed in it. A hermetic compressor has all the major components of the compressor in just one single structure. This type of system is the most common type of system and can be seen in residential, commercial, and industrial refrigeration systems.


Recall that one of the functions of refrigerant oil is to provide internal sealing of the system. The refrigerant oil forms a layer inside the system's tubings and joints. Any leak in the system would first push out the system's refrigerant oil.


This would leave oil traces on the system or the floor of the system. Oil traces is an indicator that the hermetic system is leaking. While inspecting any system, traces of oil are ideally the first signs a technician should look for.


3. Belt-Driven Non-Hermetic System


In a belt-driven non-hermetic system, the compressor motor and the compressor are in different structures and connected by a rubber belt. Unlike the hermetic type, it does not have its components in a single shell. This type of system can be seen mostly in industrial refrigeration systems.


A Rotating shaft seal is used at the junction where the metallic shaft connects to the compressor. Rotating shaft seals have rubber seals for the purpose of sealing. If a system is non-working for several months, the rubber seals become hard and cannot perform sealing, causing leaks in the system.


To reiterate the whole concept:

1. A Rotating shaft seal is used at the junction where the metallic shaft connects to the compressor.

2. In a belt-driven non-hermetic system, that has not been used for many months, the rotating shaft seal is most likely to leak.


4. Leak Detection Methods


Let us have a look at some methods to detect leaks in a system. In the absence of any specific indicators of leaks, these methods have to be used to find leaks.


Ultrasonic Leak Detectors An ultrasonic leak detector works by amplifying the sound of the gas escaping a system. Electronic Leak Detectors They have an electronic circuit in them which can detect the presence of particular refrigerants. Both methods are used to detect broad areas of a leak.


Recall that a soap bubble leak detection test is used to pinpoint the specific area of the leak. Soap bubble leak detection test is generally the most effective method of leak detection as it pinpoints leaks and tells the exact location of leaks to the technician.


Recall that in the nitrogen pressure test also called as standing pressure test, pressurized nitrogen gas is filled in the system.


A nitrogen pressure test is generally the first thing to be done for newly assembled systems or field piped split systems. A field piped system is one that has been installed on-site and not a ready-to-install factory-made system. Examples of field piped systems include residential split AC and residential heat pumps.


The number of leaks in a field piped system, or a newly assembled system depends on the technician's skill working on it. So it is important to perform a nitrogen pressure test on such systems to ensure that the system is leak-free.


Recall the use of a trace gas with nitrogen in a standing pressure test. If a trace amount of other gas is necessary during leak checking, the best choice for the trace gas is the system’s design refrigerant itself. For example, an R407C system should use R407C as a trace gas with nitrogen for leak detection.


5. Conclusion


In this module, we discussed a few indicators of leaks and particular systems in which they can be used. We also refreshed methods to detect leaks and learned about the use of trace gas while detecting leaks.


Question #1: Which of the following is an indicator of a leak in a high-pressure system with a capillary tube?

  1. High head pressure

  2. Low water temperature

  3. Excessive superheat

  4. Frequent purgingScroll down for the answer...












If a high-pressure system with a capillary tube has a high value of superheat, it is an indicator that there is a leak.


Question #2: When first inspecting a hermetic system known to be leaking, you should look for;

  1. Frost on the tubing

  2. Puddles of refrigerant

  3. Particles of filter drier core

  4. Traces of oil

Scroll down for the answer...












While inspecting any hermetic system, traces of oil are ideally the first signs a technician should look for.


Question #3: Which part of a belt-driven non-hermetic compressor is most likely to leak if the compressor has not been used for several months?

  1. Suction service valve

  2. Rotating shaft seal

  3. One or both of the king valves

  4. Head gasket on the discharge side

Scroll down for the answer...













If a belt-driven non-hermetic compressor has not been used for several months, rubber seals in the rotating shaft seals become hard.

A hard seal cannot perform its function of sealing the system. Insufficient sealing will let the refrigerant oil leak out of the system.


Question #4: To pinpoint refrigerant leaks, we use the method;

  1. Ultrasonic Leak Detector

  2. Soap Bubble Leak Detection Test

  3. Electronic Leak Detection

  4. Leak Sniffing MethodScroll down for the answer...

Scroll down for the answer...













The best use for testing a system for leaks using soap bubbles is to pinpoint the leaks.


Question #5: After installation of a field piped split system, the unit should first be pressurized with;

  1. air and leak checked.

  2. R-22 and leak checked.

  3. R-410A and leak checked.

  4. nitrogen and leak checked.

Scroll down for the answer...











Any field piped system should first be pressurized with nitrogen and leak checked. The number of leaks in a field piped system depends on the technician's skill working on it.


So it is important to perform a pressure test and detect leaks first.


Question #6: What is the first thing to do when a new system has been assembled (built up), and is ready for testing?

  1. Pull a vacuum.

  2. Pressurize with an inert gas and leak check.

  3. Pressurize with the refrigerant to be used in the system.

  4. Introduce an initial charge of refrigerant and start the compressor.

Scroll down for the answer...











Any newly assembled system should first be pressurized with nitrogen and leak checked. The number of leaks in a newly built system depends on the technician's skill working on it.


So it is important to perform a pressure test and detect leaks first.


Question #6: When a trace gas becomes absolutely necessary, which of the available gases should be used to help locate a leak?

  1. Nitrogen with HCFC R-22

  2. R-22 due to its universal system compatibility and its miscibility with various oils

  3. Nitrogen with a trace amount of the system’s design refrigerant

  4. Nitrogen with HFC R-410A

Scroll down for the answer...











If a trace amount of other gas is necessary during leak checking, the best choice for the trace gas is the system’s design refrigerant itself.


Nitrogen gas should be used along with trace gas to help locate leaks.


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