• SkillCat Team

Refrigerant Charging

EPA 608 Type 2 Chapter 11 (Take full course for free)


In this module, we will discuss the correct methods of charging a system back with refrigerant. Skip to quiz!


1. Pressure-Temperature Relations


Recall that boiling temperature is the temperature at which a liquid changes its state to vapor by boiling. The temperature at which vaporization (boiling) starts to occur for a given pressure is called the saturation temperature or boiling point.

P-T Charts have the relationship between the pressure and saturation temperature of any substance. For any refrigerant, we can know its saturation temperature at a given pressure and vice versa. P-T mean Pressure-Temperature Charts. Let us learn to read these charts.


Consider this P-T Chart for R-410A. The units for temperature are either °Fahrenheit or °Celsius, as we can see here. To find the pressure at a temperature, we look for the temperature, then look across that row for the corresponding pressure.


In the chart, the value 80 °Fahrenheit is highlighted, and it corresponds to 235 psig. For example, if an R-410A appliance is at room temperature (80 °Fahrenheit), the pressure of the refrigerant in the appliance will be 235 psig.


In the chart for R134A, the value close to 0 °Celsius is 1.7 °Celsius. The pressure of R134A at 1.7 °Celsius is 30.4 psig and is highlighted in the chart. We will discuss the use and importance of these P-T values later on in the topic.


2. Charging a System


Once you recover any refrigerant, you can fill it back in the system after the repair works.

Recall the three Rs,

  • Recover

  • Recycle

  • Reclaim

Sometimes it may be necessary to recycle the refrigerant before filling it back.

You should recycle the refrigerant if you find that the refrigerant has many impurities. Many testing kits are available that instantly tell if the recovered refrigerant needs to be recycled. However, if the repairs are only minor ones, recycling is not needed.


Liquid charging means filling the system back with liquid refrigerant. It is faster and saves time. We can initiate charging a system with liquid refrigerant in appliances that do not use water in any part/component. These are air-cooled systems.


Recall that service valves are used to access the refrigerant inside the system without opening it. We also charge the system with refrigerant via these service valves. Liquid charging is always done via the liquid-line service valve. Vapor charging is done via the suction service valve.


In systems that use water in any part or component, it becomes necessary to initiate the charging process with vapor charging. Let us understand why!


Recall that it is necessary to evacuate a system before filling it back with refrigerant. After the evacuation process, the pressure inside a system is low (about 500 microns). The evaporation point corresponding to the evacuation pressure is much lower than 0°Celsius (Freezing point of water).


If the liquid refrigerant is filled in a evacuated system, it can boil into vapor even if the temperature is less than 0°Celsius. For example, the evaporation temperature of R134a at 0 psi is -15°Fahrenheit.


Recall that when a liquid boils, it absorbs heat. While boiling, the liquid refrigerant will absorb heat from the water in the system and convert the water to ice. It is difficult to melt the ice, and at times the evaporator/condenser coils rupture and burst due to ice. This is dangerous and must be avoided.


For this reason, in systems that use water in any part/component, we initiate the charging process with vapor charging. We charge such systems with vapor till the pressure inside the system increase.


Vapor charging is done till the pressure rises to a corresponding boiling temperature of 0°Celsius or more.


The refrigerant R-134A can boil at 0 °Celsius when the pressure is less than 30 psig. While charging, an R-134A system is filled with vapor refrigerant until the pressure rises to 30 psig. Similarly, the refrigerant R410A can boil at 0 °Celsius when the pressure is less than 110 psig.


3. Conclusion


In this module, we learned the correct methods of charging a system back with refrigerant. We also learned a few pressure-temperature values that are expected to be memorized by the student.


Question #1: What is the approximate refrigerant pressure of an R-410A machine at 80 °Fahrenheit while the machine is idle?

  1. 143 psig

  2. 212 psig

  3. 238 psig

  4. 260 psig

Scroll down for the answer...











238 psig

If an R-410A appliance is at 80 °Fahrenheit, the pressure of the refrigerant in the appliance will be 235 psig.

The most approximate answer would be 238 psig.


Question #2: The refrigerant has been recovered to replace the evaporator coil in an appliance. After the repairs, the refrigerant;

  1. can be filled back into the system.

  2. can be sold as it is to another equipment owner.

  3. must be reclaimed.

  4. must be destroyed.

Scroll down for the answer...











can be filled back into the system.

Any recovered refrigerant can be filled back into the system once the repairs are done.


Question #3: How can we charge a system having 80 pounds of R407C and has both an air-cooled condenser and evaporator?

  1. Vapor charge through the suction service valve.

  2. Vapor charge through the liquid-line service valve.

  3. Liquid charge through the suction service valve.

  4. Liquid charge through the liquid-line service valve.

Scroll down for the answer...











Liquid charge through the liquid-line service valve.

We can use liquid charging in a system that has an air-cooled condenser and evaporator coils. As these systems do not have water, there is no risk of freezing during liquid charging.

Liquid charging is always done via the liquid-line service valve.


Question #4: What is the evaporation temperature of R-134a at 0 psig?

  1. -21°Fahrenheit

  2. -15°Fahrenheit

  3. -5°Fahrenheit

  4. -1°Fahrenheit

Scroll down for the answer...











-15°Fahrenheit

The evaporation temperature of R134a at 0 psig is -15°Fahrenheit.


Question #5: The risk of freezing while charging an R-410A appliance will remain till from a vacuum level to a pressure of approximately;

  1. 32 psig.

  2. 63 psig.

  3. 90 psig.

  4. 110 psig.

Scroll down for the answer...











110 psig.

The refrigerant R410A can boil at 0°Celsius when the pressure is less than 110 psig.

Once the pressure reaches 110 psig, there is no risk that the water in the appliance will freeze.


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