Technician’s Guide and Workbook for the EPA Section 608 Test Section 5: Core Part 4

Refrigeration Topics in this section: Refrigerant states (vapor versus liquid) and pressures at different points of refrigeration cycle; how/when cooling occurs Refrigeration gauges (color codes, ranges of different types, proper use) Refrigeration service valves Leak detection Leak rate Leak rules for systems of 50 pounds or more

Refrigerant States Refrigerants used for refrigeration and air conditioning are working fluids that absorb heat as low-pressure, low-temperature gas in the evaporator and release the heat as a high-pressure, high-temperature gas in the condenser. As the refrigerant moves through the air conditioning or refrigeration system it changes state between liquid and gas.

Important Refrigerant Concepts (1) Hygroscopic refrigerants and lubricating oils readily absorb moisture. Steps must be taken to keep these refrigerants and lubricants sealed in their containers so that excess moisture is not introduced into the HVACR system. Azeotropic refrigerants contain two or more refrigerants that act like pure refrigerants. That is, all components evaporate and condense at constant temperatures.

Important Refrigerant Concepts (2) Zeotropic refrigerants are the opposite of azeotropic refrigerants: their components condense and evaporate at different temperatures. This causes temperature glide. Hence, the refrigerant does not condense at a single temperature nor evaporate at a single (higher) temperature. Rather, evaporation occurs over a range of temperatures at a given pressure and condensing occurs over a different range of temperatures at a given pressure. The larger the difference in the refrigerant components’ boiling points (i.e., the temperature range where the components evaporate) the larger the mass shift in the refrigerant. A refrigerant with a large glide will also have more of the refrigerant separated during the refrigeration cycle. In the case of a leak, this may cause zeotropic refrigerants to lose more of one chemical part of the mixture than another, depending on where the leak is in the refrigerant cycle.

Important Refrigerant Concepts (3) Fractionation is the change in the chemical balance in a blended refrigerant when some of the refrigerant components are lost (removed/leaked) faster than others. This will cause an imbalance that may affect the refrigerants’ ability to operate properly within the system. Blended refrigerants may be azeotropic or zeotropic mixtures of two components (binary), three components (ternary), or more.

Important Refrigerant Concepts (4) During the refrigeration cycle, some of the oil mixes with refrigerants and forms a homogenous solution. This property of mixing by fully dissolving into each other is called miscibility. Oil in its pure form has different qualities than oil mixed in refrigerant. Refrigerant gas dissolves into lubrication oil, and liquid oil dissolves into refrigerant vapor/gas. Either way, when oil mixes with refrigerant, the oil’s ability to act as a lubricant (its viscosity) decreases. Hence, it is important to always use the lubricant specified by the equipment manufacturer; the oil must be matched to the refrigerant and the refrigerant’s usage.

Important Refrigerant Concepts (5) During the refrigeration cycle, some of the oil mixes with refrigerants and forms a homogenous solution. This property of mixing by fully dissolving into each other is called miscibility. Oil in its pure form has different qualities than oil mixed in refrigerant. Refrigerant gas dissolves into lubrication oil, and liquid oil dissolves into refrigerant vapor/gas. Either way, when oil mixes with refrigerant, the oil’s ability to act as a lubricant (its viscosity) decreases. Hence, it is important to always use the lubricant specified by the equipment manufacturer; the oil must be matched to the refrigerant and the refrigerant’s usage.

Important Refrigerant Concepts (5) Common oils and the refrigerants they are generally used with are listed below: Mineral oil (MO) and alkylbenzene oil (AB) provide good miscibility and stability with HCFC refrigerants such as R-22, R-12, R-123, R-124, R-401a, R-401b and R-402a. Polyolester oil (POE) provides superior protection and performance with HFC refrigerants such as R-23, R-134a, R-407C and R410A. Polyalkylene (PAG) provides superior protection and performance with HFC refrigerants such as 134a and HFO R-1234y. Notes on oils: No refrigerant oils should be mixed with other families of oils. When a refrigerant is changed within a given system, the old oil must be removed and the refrigerant-specific lubricant added.

Basic Refrigerant Cycle In the sketch above, the high-pressure side of the system (generally the outdoor components) is represented in red and the low-pressure side (generally the indoor components) is in blue.

Basic Refrigerant Cycle 1. Low-temperature, low-pressure (cold) refrigerant vapor/gas with refrigerant droplets mixed in at 40OF flows through the evaporator (1) and as the 78°F return air from the conditioned space passes through the evaporator coils, heat is transferred from the warm air to the refrigerant resulting in the air moving from the evaporator to the conditioned space being 50°F.

Basic Refrigerant Cycle 2. The warmer refrigerant moves on as a superheated vapor/gas to the compressor (2) low side (or suction side) where the refrigerant pressure is increased by mechanical compression and exits the compressor high side as a high-pressure, hot vapor/gas.

Basic Refrigerant Cycle 3. The refrigerant then passes through the condenser (3) where “relatively cool” 90°F outside air flows across the condenser fins that have been heated to about 112°F by the refrigerant flowing through the condenser tubes. The air temperature leaving the condenser is heated to 102°F, while the refrigerant is cooled down to 100°F as it exits the condenser as a high-pressure, intermediate-temperature liquid.

Basic Refrigerant Cycle 4. The high-pressure, intermediate-temperature liquid passes through the expansion device (4) where it is turned into a low-temperature, low-pressure liquid droplet and vapor/gas mixture. The lowering of the pressure results in the refrigerant temperature dropping back to 40°F.

Basic Refrigerant Cycle 5. The cycle repeats.

Refrigeration Gauges (1) Refrigerant gauges should be rated for the refrigerant in the system. They need to be in good condition and should read the pressures in the system accurately. Refrigerant gauges should be equipped with anti-blowback valves or shutoff ball valves that stop the refrigerant from leaking out of the hoses when the hoses are disconnected. After closing the service valves, it is good practice to remove the high-side hose first, open the center valve so the hoses can equalize pressure to the low-side pressure, then remove the low-side hose. Preferably, each gauge set should only be used for one type of refrigerant to avoid cross-contamination of refrigerants and lubricants. When this is not possible, the line sets should be free of other refrigerants to avoid the mixing of refrigerants in systems. A best practice is to purge and evacuate all hoses after each use.

Refrigerant Gauges (2) The basic analog gauge set has two gauges and a manifold with three hoses, and allows for system refrigerant charging, pressure measurements and refrigerant recovery. One of the two gauges is a high-pressure gauge that is often colored red, while the other is a low-side gauge often colored blue. For U.S. applications, both gauges generally have a PSI (pounds per square inch) reading scale and are designed for use with one or more types of refrigerants. The high-pressure gauge generally has a range up to 800 PSI, while the low-pressure compound gauge has a calibrated pressure range up to 300 PSI (many gauges can go up to 500 PSI). In addition to the pressure scale, they also have the corresponding refrigerant temperature for the designated pressure. The high-side gauge is designed to be connected to the refrigeration system’s high-side port. The low-side compound gauge is connected to the low-side access port and measures suction-side pressure (PSI) and vacuum in inches of mercury. Electronic gauge sets generally display high and low pressures on one screen, as shown in Figure 15. Electronic gauges cost more than analog gauges, but offer increased functionality, capability, and accuracy that can significantly improve the process.

Refrigeration Service Valves Service valves are connected to the OEM condenser or compressor. There are generally at least two valves: one for the discharge/high side and one for the suction/low side. Service valves are three-position valves; turning the handle clockwise opens the valve. The Figure below shows an internal view of the valve in the three positions. Back-seating is a term used for when the valve is closed off to the service port. 1. Service port 2. To condenser or compressor 3. Line set to system

Leak Detection Leaks on all systems must be located and repaired before refrigerant is added to a system. Owners or operators must take corrective action when an appliance with a full charge of 50 or more pounds is discovered to be leaking an ozone-depleting refrigerant at a rate that exceeds the applicable trigger rate. Starting January 1, 2019, these requirements will also apply to appliances containing substitute refrigerants.

Leak Rate The leak rate is the rate at which an appliance is losing refrigerant, as measured between refrigerant charges. The same leak rate method must be used for all appliances subject to the leak repair requirements located at an operating facility. Additionally, the leak rate is expressed in terms of the percentage of the appliance's full charge that would be lost over a 12-month period if the current rate of loss were to continue over that period.

Leak Rate Rules for Systems containing 50 Pounds or More of Refrigerant (1) The following provisions apply to owners and operators of appliances containing 50 or more pounds of Class I and Class II refrigerants only until January 1, 2019. Owners or operators of commercial refrigeration equipment normally containing more than 50 pounds of refrigerant must have leaks repaired in accordance with this section if the appliance is leaking at a rate such that the loss of refrigerant will exceed 35 percent of the total charge during a 12-month period. Repairs must bring the annual leak rate to below 35 percent.

Leak Rate Rules for Systems containing 50 Pounds or More of Refrigerant (1) If the owners or operators of the federally-owned commercial refrigerant appliances determine that the leaks cannot be repaired in accordance with the paragraph above without an extension, they must document all repair efforts and notify the EPA of their inability to comply within the 30-day repair requirement. The reason for the inability to conform must be submitted to the EPA in accordance with §82.166(n). Such notification must be made within 30 days of discovering the leaks. The EPA will determine if the extension requested is justified in accordance with the requirements. If the extension is not justified, the EPA will notify the owner/operator within 30 days of receipt of the notification. Owners or operators of federally-owned commercial refrigeration equipment may have more than 30 days to repair leaks if the refrigeration appliance is located in an area subject to radiological contamination or where shutting down the appliance will directly lead to radiological contamination. Only the additional time needed to conduct and complete repairs in a safe working environment will be permitted. Owners or operators of federally-owned commercial refrigeration equipment requesting or granted time extensions under this paragraph must comply with the application requirements listed above.