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Key Components

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

In this module, we will learn about the chillers and different components used in Type 3 appliances. Skip to quiz!

1. Chiller Components

Recall that chillers are cooling systems that work under a vacuum. Chillers have water flowing over the evaporator coils. So, instead of providing cool air, chillers provide cold water.

The cold water is then used to cool office spaces or used in other industrial applications. There are two main types of chillers based on the type of condenser:

  1. Air-Cooled Chillers, and

  2. Water-Cooled Chillers

We will learn about their working and key components in detail.

Air-cooled chillers have condensers that use surrounding air to cool hot refrigerants. The heat from the condenser is released to the air. This is similar to any residential split AC or heat pump.

Contrastingly, water-cooled chillers use water to cool the refrigerant in the condenser. The water flows over the condenser tubes and absorbs the excess heat. Cold water is used to absorb the heat from the hot refrigerant in the condenser tubes.

The cold water require to cool the condenser tubes is produced by the cooling towers. A cooling tower is a large heat exchanger unit that provides cooling water to remove heat from the refrigerants.

Recall that a chiller produces cold water by passing it through the evaporator and condenser barrels. It does so by passing copper tubes that carry water through barrels of refrigerant. The barrel carries refrigerant, and the tubes carry water for cooling.

The water-circulating pumps pump the water as they flow continuously through the tubes. The water is never allowed to mix with the refrigerant in the refrigeration cycle. Keep in mind that the water cycle and refrigeration cycle are entirely separate.

2. Water Box

A water box is a part of any chiller and performs the function of directing water flow. It also separates the entrance and the exit of the water into the condenser tubes. It is mounted on the evaporator and condensers of water-cooled chillers.

The water box also performs the function of sealing the chiller barrel tubes from the outside. Evaporator tubes are known as chiller barrel tubes. Keep this in mind as these names are used interchangeably.

3. Purge Unit

Recall that the vacuum in Type 3 appliance wants to suck everything inside it, but it is tightly sealed. All low-pressure systems have purge units to vent or remove air and moisture that enter due to leaks. The term “purge” means to remove something.

In the refrigeration appliance, the air entered into the system collects at top or highest point in the system. This is similar to how air bubbles in a bottle of water collects at the top. The collected air and moisture is then thrown out of the system by the purge unit.

In the refrigeration system, the far end of the condenser is where the air collects. As a result, this is where the technicians should make the purge unit connection.

The purge unit is located at the top of the condenser coils. The refrigerant is sucked into the purge unit from the top of the condenser. The refrigerant free from air and moisture is then sent to the evaporator through the expansion valve.

While the purge unit is operating, the refrigerant might exit the system along with air and moisture. A high-efficiency purge unit will remove minimal refrigerant along with the air. On the other hand, an inefficient purge unit will continue to leak refrigerant in large amounts.

4. Rupture Disc

A rupture disc is a safety disc that protects the system from getting over-pressurized. As Type 3 appliances operate at very low pressures, over-pressurization is a common mistake by many technicians. Over-pressurization causes the tubes in the appliance to burst and must be prevented at all costs.

The rupture disc is located on the evaporator of a chiller. While charging the system, we charge it through the charging valve of the evaporator. A charging valve is a port that allows a controlled flow of the refrigerant fluid in or out of the system.

The rupture disc in a chiller is set at a pressure of 15 psig. This pressure is known as safety-relief pressure. If the systems' pressure exceeds 15 psig, the rupture disc will burst, venting the refrigerant out of the system.

Recall that charging means filling the system with refrigerant. The pressure while charging through the evaporator valve should not exceed 10 psig. The difference of 5 psig (15-10) is kept while charging the system for safety purposes.

5. Drain Valve

A drain valve in a chiller performs the function of allowing excess water vapor to escape into the atmosphere. The excess water vapor in a chiller finds its way into the compressor and other parts where it should not go. Releasing the moisture helps to prevent corrosion that eventually damages the compressor and shortens its lifespan.

6. Conclusion

In this module, we went over the key components of Type 3 appliances. We studied their types and significance. We also went over a few types of compressors used in different appliances.

Question #1: After the refrigerant leaves the purge unit, where does it go?

  1. Condenser

  2. Recovery Cylinder

  3. Evaporator

  4. Compressor

Scroll down for the answer...


The refrigerant from the purge unit free from air and moisture enters the evaporator through the expansion valve.

Question #2: Which of the following components are only found in Type 3 appliances?

  1. Compressor

  2. Purge Unit

  3. Condenser

  4. Evaporator

Scroll down for the answer...

Purge Unit

Purge unit removes non-condensables that enter the low-pressure system when there is a leak in it.

Question #3: What is the safety-relief pressure of the rupture disc?

  1. 10 psig

  2. 15 psig

  3. 5 psig

  4. 20 psig

Scroll down for the answer...

15 psig

The rupture disc is set to burst at 15 psig. This pressure is also known as the safety-relief pressure.


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