CFC System Charging & Evacuation 5 — Questions and Answers
Question 1: When charging a system using the superheat method, which condition represents a correctly charged system?
- Actual superheat equals target superheat from the manufacturer's charging chart (Correct answer)
- Suction pressure equals discharge pressure divided by two
- The liquid line feels warm to the touch
- The sight glass shows 50% liquid
Correct answer: Actual superheat equals target superheat from the manufacturer's charging chart
The superheat method is correct when measured suction superheat matches the target value from the manufacturer's or industry charging chart for the given conditions.
Question 2: What refrigerant handling practice is specifically prohibited by EPA Section 608 regulations?
- Using refrigerant cylinders as a heat source to increase transfer speed (Correct answer)
- Transferring refrigerant between recovery cylinders
- Adding refrigerant to a system to bring it to operating pressure
- Using nitrogen to pressurize a system for leak testing
Correct answer: Using refrigerant cylinders as a heat source to increase transfer speed
Applying heat directly to refrigerant cylinders is prohibited because it can raise internal pressure beyond the cylinder's rated capacity, creating an explosion hazard.
Question 3: A technician notices the micron gauge reading drops rapidly to below 200 microns but then slowly rises to 800 microns and stabilizes. This most likely indicates:
- A refrigerant leak into the system
- Residual moisture in the system that is outgassing (Correct answer)
- The vacuum pump is too small for the system
- A faulty micron gauge
Correct answer: Residual moisture in the system that is outgassing
A rise that stabilizes after pump isolation indicates outgassing of moisture, which produces water vapor that raises the pressure to a level consistent with the dew point at that temperature.
Question 4: Which hose configuration maximizes evacuation speed when using a vacuum pump?
- Standard 1/4-inch charging hoses connected to both manifold ports
- Large-diameter (3/8-inch core or larger) hoses connected directly to the system service valves (Correct answer)
- A single 1/4-inch hose on the low side only
- Any hose configuration, as pump CFM rating is the only factor
Correct answer: Large-diameter (3/8-inch core or larger) hoses connected directly to the system service valves
Large-diameter hoses connected directly to the system (bypassing the manifold if possible) minimize flow restriction and allow the vacuum pump to work at maximum efficiency.
Question 5: What must a technician do if a recovery cylinder's pressure relief valve opens during refrigerant recovery?
- Continue recovery and note the event in the service record
- Stop recovery immediately, move the cylinder to a safe area, and do not reuse it without inspection (Correct answer)
- Reseat the valve by pressing it closed and proceed
- Add nitrogen to re-pressurize the cylinder and continue
Correct answer: Stop recovery immediately, move the cylinder to a safe area, and do not reuse it without inspection
An opened pressure relief valve indicates the cylinder reached or exceeded its rated pressure; operations must stop and the cylinder must be inspected before further use.
Question 6: Which of the following is the correct procedure for charging a system that was opened for compressor replacement?
- Charge with refrigerant immediately after installing the new compressor
- Pressure test with nitrogen, evacuate to below 500 microns, verify vacuum holds, then charge by weight (Correct answer)
- Pull a 15-minute vacuum and charge without a standing vacuum test to save time
- Charge refrigerant until the sight glass clears, then verify superheat
Correct answer: Pressure test with nitrogen, evacuate to below 500 microns, verify vacuum holds, then charge by weight
After opening a system, proper procedure requires nitrogen pressure testing, deep evacuation, a standing vacuum test to confirm no leaks or moisture, and then charging by weight per nameplate specifications.
Question 7: In the context of system charging, what does 'subcooling' measure?
- The temperature difference between the suction gas and the evaporating refrigerant
- The number of degrees the liquid refrigerant is cooled below its saturation temperature at the condenser outlet (Correct answer)
- The pressure drop across the metering device
- The heat removed by the evaporator per unit time
Correct answer: The number of degrees the liquid refrigerant is cooled below its saturation temperature at the condenser outlet
Subcooling is the difference between the saturation temperature at the condenser pressure and the actual liquid line temperature, indicating how much the liquid has been cooled below its boiling point.
CFC System Charging & Evacuation 5
When charging a system using the superheat method, which condition represents a correctly charged system?