EPA 608 Technician Certification High-Pressure Systems, Refrigerants, and Safety Summary

40 CFR 82.152 defines a high-pressure appliance as one using a refrigerant with a liquid saturation pressure between 170 and 355 psia at 104°F. Examples are R-22, R-407A, R-407C, R-410A, and R-502.

Wrong choices

• R-11: R-11 is a low-pressure refrigerant.
• R-123: R-123 is a low-pressure refrigerant.
• R-134a: R-134a is a medium-pressure refrigerant (still covered by Type II).

The receiver sits after the condenser on the high side and stores liquid refrigerant. The refrigerant in it is a high-pressure liquid, which is why refrigerant can be pumped down into the receiver to isolate it.

Wrong choices

• To absorb heat from the space: Absorbing heat is the evaporator's job.
• To remove air from the system: Removing air is done by evacuation or a purge unit.
• To compress vapor: Compressing vapor is the compressor's job.

The appliance nameplate lists the refrigerant type and charge. A pressure and temperature check with a PT chart can confirm it.

Wrong choices

• Look at the color of the refrigerant lines: Line color does not identify the refrigerant.
• Smell the refrigerant: Smelling refrigerant is unsafe and does not identify it.
• Ask the building owner to guess: A guess is not reliable.

In a deep vacuum there is very little gas to cool the motor and insulate the terminals, so starting a hermetic compressor under vacuum can damage the motor windings. EPA lists this as a Type II safety topic.

Wrong choices

• It will clean the oil: It does not clean the oil.
• It will make the vacuum deeper and faster: Running the compressor under vacuum risks damage and is not how a vacuum is pulled.
• It will recover the refrigerant automatically: It does not perform recovery.

An accumulator is placed in the suction line before the compressor. It traps liquid refrigerant so only vapor reaches the compressor, protecting it from liquid slugging.

Wrong choices

• To store extra oil for the condenser: An accumulator is not an oil storage tank for the condenser.
• To measure the refrigerant charge: It does not measure the charge.
• To raise the pressure of the liquid line: It is on the low side and does not raise liquid line pressure.

EPA's Type II test topics include the idea that hydrocarbons are not approved for retrofits. Flammable refrigerants are allowed only in equipment designed for them.

Wrong choices

• Yes, but only in the winter: The season does not matter.
• Yes, any hydrocarbon can be added on top of R-22: Adding a hydrocarbon to R-22 would mix refrigerants and create a fire hazard.
• Yes, if the system holds less than 50 pounds: System size does not make a hydrocarbon retrofit acceptable.

EPA's test topics note that ASHRAE Standard 15 equipment room rules call for a refrigerant or oxygen-deprivation sensor with an alarm, because leaking refrigerant can push out oxygen.

Wrong choices

• No device is needed if a window is open: An open window does not meet the standard.
• A smoke detector only: A smoke detector does not detect refrigerant.
• A carbon monoxide detector only: A carbon monoxide detector does not detect refrigerant.

After the evaporator, the refrigerant is a low-pressure vapor in the suction line on its way to the compressor. The liquid line and receiver hold high-pressure liquid, and the discharge line carries high-pressure vapor.

Wrong choices

• The discharge line between the compressor and the condenser: The discharge line carries high-pressure vapor.
• The receiver: The receiver holds high-pressure liquid.
• The liquid line between the condenser and the metering device: The liquid line carries high-pressure liquid.

EPA's test topics remind technicians to add 14.7 to change gauge pressure into absolute pressure.

1. psia = psig + 14.7
2. 100 + 14.7 = 114.7 psia
3. Check: 114.7 - 14.7 = 100 psig

Wrong choices

• 85.3 psia: This subtracts 14.7 instead of adding it.
• 100 psia: Gauge and absolute pressure are not equal.
• 129.4 psia: This adds 14.7 twice.

A very high-pressure appliance uses a refrigerant with a critical temperature below 104°F or a liquid saturation pressure above 355 psia at 104°F. Examples are R-13, R-23, R-503, R-508A, and R-508B.

Wrong choices

• R-134a: R-134a is medium-pressure.
• R-22: R-22 is high-pressure, not very high-pressure.
• R-123: R-123 is low-pressure.