EPA 608 Type 3 Chapter 9 (Take full course for free)
In this module, we will discuss the process of evacuating a system. We will also learn many tips and techniques to perform a successful evacuation. Skip to quiz!
1. Recovery Procedure
Evacuation is when we remove all water vapor and air from the refrigeration system. We evacuate a system before filling it back with refrigerant to avoid mixing refrigerant with air. We do this by sucking out all the air and creating a vacuum inside the appliance.
Recall that a vacuum pump is used to evacuate the system to the required levels. In chillers, the cooling water or moisture from the outside air can leak into the system. Evacuation is the final step to remove all these before filling the system back with refrigerant that we already recovered.
The required levels of evacuation for low-pressure systems are:
25 mm Hg for equipment manufactured before November 15, 1993.
25 mm Hg absolute for equipment manufactured after November 15, 1993.
Recall that the term absolute means pressure measured with respect to vacuum.
When repaired for any leaks, all low-pressure systems and chillers must be evacuated till the mentioned levels of pressure. After reaching the required vacuum on an appliance, a technician should wait for at least a few minutes. If the system holds the level of vacuum, it confirms that the system is not leaking anymore.
Before disposing of a low-pressure appliance, it must be evacuated as per the regulations to prevent venting of refrigerants in the atmosphere. The equipment must be evacuated to 25 mm Hg absolute before disposal.
2. Factors Affecting Evacuation
Recall the pressure-temperature relations for any fluid. The pressure and temperature of any system are directly related to each other. A reduction in pressure results in a drop in the temperature of the system.
While evacuation, as the pressure is decreasing, the temperature of the system is also falling. There is a possibility that the water gets converted into ice at very low temperatures. If ice is formed, it clogs the refrigerant piping and must be avoided.
Technicians can use a special technique to avoid freezing. We stop evacuation in between and increase the pressure by releasing some nitrogen gas into the system.
The nitrogen gas increases the pressure and temperature before freezing the does not allow the moisture to accumulate in one place. The gas, along with water, is then removed from the system by the evacuation process. It prevents freezing of the moisture inside the system.
Using a large vacuum pump leads to a faster evacuation, but ice formation is a peculiar problem. The pressure (and temperature) in the system reduces very quickly during evacuation and can cause the water in the system to freeze and form ice.
3. Conclusion
In this module, we learned many things about evacuating a system. We also discussed some tips and techniques to perform a successful evacuation. Understanding these concepts will help us in perfectly evacuating a system.
Question #1: Identify the recovery requirements for equipment disposal
0 psig
15 inches of Hg vacuum
25 inches of Hg vacuum
25 mm of Hg absolute
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25 mm of Hg absolute
Before disposing of a low-pressure appliance, it must be evacuated as per the regulations to prevent venting of refrigerants in the atmosphere. The equipment must be evacuated to 25 mm Hg absolute before disposal.
Question #2: Which gas is used to counteract freezing while evacuating a system with large amounts of moisture;
R-410A.
R-22.
Air.
Nitrogen.
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Nitrogen
The nitrogen gas released in a system during evacuation carries the moisture along with it. This does not allow the water to accumulate in one place. It prevents freezing of the moisture inside the system.
Question #3: Water present in the system can freeze if;
A large vacuum pump is used for evacuation
A recovery unit is used for evacuation
The system’s compressor is used for evacuation
A house vacuum cleaner is used for evacuation
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A large vacuum pump is used for evacuation
The system's pressure (and temperature) can reduce very quickly while evacuating with a large vacuum pump. This sudden decrease in temperature can cause the water in the system to freeze and form ice.