CFC System Charging & Evacuation 3 — Questions and Answers
Question 1: What does a micron gauge reading of 500 microns or below typically confirm during system evacuation?
- The system is charged to the correct operating pressure
- The system has achieved an adequate vacuum for most refrigeration applications (Correct answer)
- The refrigerant blend ratio is correct
- The high-side pressure is within specification
Correct answer: The system has achieved an adequate vacuum for most refrigeration applications
A reading of 500 microns or below indicates a deep vacuum sufficient to remove moisture and non-condensables for most HVAC/R applications before charging.
Question 2: Why should a technician never use a manifold gauge set's sight glass to determine when evacuation is complete?
- Manifold gauges are not accurate enough below 0 psig to measure true vacuum depth (Correct answer)
- Sight glasses only work with liquid refrigerant
- Manifold gauges cannot be connected during evacuation
- Sight glasses measure superheat, not vacuum level
Correct answer: Manifold gauges are not accurate enough below 0 psig to measure true vacuum depth
Standard manifold gauges lack the resolution to measure the deep vacuum levels required; an electronic micron gauge is needed to verify adequate evacuation.
Question 3: When charging by weight, which tool is essential for accuracy?
- Clamp-on ammeter
- Calibrated refrigerant charging scale (Correct answer)
- Digital manifold gauge set
- Sling psychrometer
Correct answer: Calibrated refrigerant charging scale
A calibrated refrigerant charging scale measures the exact weight of refrigerant transferred into the system as specified by the manufacturer.
Question 4: What happens to vacuum pump performance if the pump oil becomes contaminated with moisture?
- The pump pulls a deeper vacuum faster
- The pump's ultimate vacuum capability decreases significantly (Correct answer)
- Oil contamination has no effect on ultimate vacuum depth
- The pump automatically shuts off to prevent damage
Correct answer: The pump's ultimate vacuum capability decreases significantly
Water-contaminated vacuum pump oil cannot maintain the required low vapor pressure, degrading the pump's ability to achieve deep vacuum levels.
Question 5: Which of the following refrigerants requires the technician to charge from the vapor phase only on the low side?
- R-410A
- R-404A
- R-22 (Correct answer)
- R-407C
Correct answer: R-22
R-22 is a single-component (azeotrope-like) refrigerant that can be charged as vapor on the low side without fractionation concerns, making vapor charging standard practice.
Question 6: A system's low-side pressure rises to suction saturation levels immediately after the vacuum pump is turned off, even after achieving 300 microns. What is the most likely cause?
- The system has a non-condensable gas problem
- There is a leak in the system that is allowing air in (Correct answer)
- The vacuum pump was running too fast
- The refrigerant charge was added too quickly
Correct answer: There is a leak in the system that is allowing air in
A rapid pressure rise to saturation levels after pump shutoff indicates a leak is allowing air (or refrigerant vapor) into the system rather than outgassing of residual moisture.
Question 7: EPA regulations require that recovery equipment manufactured after November 15, 1993, must achieve what vacuum level before opening a system or making repairs?
- 0 psig
- 4 in Hg
- 10 in Hg
- Levels defined by the equipment's certification standard (ARI 740) (Correct answer)
Correct answer: Levels defined by the equipment's certification standard (ARI 740)
EPA Section 608 requires technicians to recover refrigerant to levels established by ARI Standard 740, which vary by refrigerant type and system size.
CFC System Charging & Evacuation 3
What does a micron gauge reading of 500 microns or below typically confirm during system evacuation?