Compressor & Component Diagnostics Flashcards
7 cards from real CFC practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Compressor & Component Diagnostics flashcards as text
A technician finds that a compressor trips on the high-pressure control shortly after startup. The condenser is clean and fans are running. What diagnostic step should be performed next?
Answer: Check the refrigerant charge and look for non-condensables in the system
Non-condensable gases (air, nitrogen) trapped in the system cause abnormally high head pressure that triggers the high-pressure control, and overcharge also elevates head pressure.
Which symptom would indicate a restriction in the compressor's suction strainer screen?
Answer: High superheat and low suction pressure with normal subcooling
A plugged suction strainer restricts refrigerant vapor flow to the compressor, causing low suction pressure and high superheat due to reduced mass flow.
When checking a compressor for electrical faults using an ohmmeter, an open reading between the common and run terminals indicates:
Answer: An open winding requiring compressor replacement
An open reading (infinite resistance) between motor terminals indicates a broken winding, meaning current cannot flow and the compressor must be replaced.
A rotary vane compressor exhibits decreasing capacity over time. Inspection reveals worn vanes. What is the primary effect of worn vanes on system performance?
Answer: Decreased volumetric efficiency due to increased internal bypass leakage
Worn vanes allow refrigerant gas to bypass from the high-pressure to the low-pressure side within the compressor, reducing volumetric efficiency and system capacity.
A technician is diagnosing a screw compressor that has excessive vibration at startup. The refrigerant oil separator appears full. What is the most likely cause?
Answer: Refrigerant migration into the oil causing flashing during startup
Refrigerant that migrates and dissolves in compressor oil during off-cycles flashes violently at startup when pressure drops, causing severe vibration and oil foaming.
After replacing a failed hermetic compressor on a CFC system, the technician should perform which procedure to prevent premature failure of the new compressor?
Answer: Flush the system with nitrogen and install a new filter-drier
Flushing with nitrogen removes acid, debris, and moisture from the system, and installing a new filter-drier ensures these contaminants do not damage the replacement compressor.
A compressor's actual amp draw exceeds its rated FLA by 20% with normal system pressures. What is the most likely cause?
Answer: Supply voltage below the minimum nameplate rating
Low supply voltage causes compressor motors to draw more current (amps increase as voltage decreases) to maintain the same power output, potentially exceeding the FLA rating.