Red Seal Refrigeration & AC Mechanic (313A)
Official Timed Mock Exam Simulator

Worked Explanation: According to standard lockout/tagout procedures, verifying zero electrical potential using a calibrated voltage tester is a mandatory step after de-energizing and locking out equipment, and before commencing work. This ensures the equipment is truly de-energized and cannot be re-energized inadvertently. Attempting to start the equipment (B) is part of verifying isolation but is not the primary method for confirming zero electrical potential at the work point. Informing personnel (A) is good practice but not the critical next safety step for the individual. Tagging (D) is part of the LOTO process but not the verification of zero energy.

Worked Explanation: CSA B52 (e.g., Clause 11.2.3.2) specifies that brazing alloys used for refrigerant piping shall have a melting point above 540°C (1000°F). It does not explicitly require a minimum silver content, as phosphorus-copper (Phos-Copper) alloys, such as BCuP-2 or BCuP-5, which contain no silver or minimal silver, are commonly used and meet strength requirements for R-410A applications. The key is the melting point and strength for the required operating pressures, not necessarily silver content. Therefore, 0% silver content is permissible if the alloy meets other strength and melting point criteria.

Worked Explanation: First, calculate the superheat and subcooling from the given readings: Superheat (SH) = Suction Line Temperature - Evaporator Saturation Temperature SH = 12°F - 0°F = 12°F Subcooling (SC) = Condenser Saturation Temperature - Liquid Line Temperature SC = 95°F - 85°F = 10°F Comparing these to the design specifications: Design SH: 10°F, Actual SH: 12°F (Actual is 2°F higher than design) Design SC: 8°F, Actual SC: 10°F (Actual is 2°F higher than design) Both the superheat and subcooling are higher than their respective design targets. High superheat typically indicates a starved evaporator (undercharge, restricted metering device, low load). High subcooling typically indicates an overcharge or a restriction in the liquid line/condenser outlet. When both superheat and subcooling are elevated, a common cause is a liquid line restriction (e.g., a partially plugged filter drier, kinked line, or partially closed king valve) or a system operating under very light load with an incorrect charge. An overcharged system would usually have low superheat, and an undercharged system would typically have low subcooling. Therefore, option A provides the most plausible diagnostic implication for both values being above design.