Troubleshooting and System Diagnosis Flashcards

A technician measures a very high condenser entering air temperature of 115°F on a rooftop-adjacent unit. How does this affect system diagnosis?

Answer: It lowers subcooling and reduces system capacity

High entering air temperature to the condenser reduces heat rejection efficiency, raising head pressure and reducing subcooling and overall system capacity.

What is the significance of measuring refrigerant pressure at both the high-side and low-side service ports simultaneously during diagnosis?

Answer: It allows calculation of pressure differential to assess compressor performance and refrigerant state

Simultaneous high- and low-side pressure readings allow the technician to calculate compression ratio and compare system pressures to expected values for the given conditions.

A technician finds the suction line is sweating heavily all the way back to the compressor. What does this indicate?

Answer: Refrigerant overcharge or metering device stuck open, flooding liquid to the compressor

Heavy sweating along the full suction line back to the compressor indicates refrigerant is returning as liquid, which can cause liquid slugging and compressor damage.

When checking for a refrigerant non-condensable gas contamination, what symptom would be most evident?

Answer: High head pressure that does not correspond to expected saturation temperature

Non-condensable gases (such as air or nitrogen) cannot condense in the condenser, causing abnormally high head pressure relative to the saturation temperature.

A residential system is charged by weight per manufacturer specifications, but superheat is still too high after charging. What should the technician do next?

Answer: Check for airflow restrictions, TXV operation, or refrigerant distribution issues

When charge weight is correct but superheat is still high, the issue is likely related to airflow, metering device function, or refrigerant distribution rather than charge level.

A technician discovers that a system's operating pressures are within normal range, but the compressor body is abnormally hot. What should be evaluated?

Answer: Suction gas returning to cool the compressor, motor winding integrity, and ambient temperature

Overheating compressors with normal pressures may suffer from inadequate suction gas cooling, high ambient temperature, or motor winding problems causing excess heat generation.

A technician is diagnosing a system and finds the measured evaporator saturation temperature is 45°F but the suction line temperature at the evaporator outlet is 75°F. What is the superheat?

Answer: 30°F

Superheat equals the actual suction line temperature minus the saturation (boiling) temperature: 75°F − 45°F = 30°F.