Typical operating pressures for R-12 vapour-compression units For medium-temperature refrigerating units using R-12, which of the following is a representative condenser-side operating pressure?

Introduction / Context:Approximate operating pressures help technicians and students check gauges, anticipate component ratings, and identify faults. R-12 (legacy refrigerant) typically runs at moderate condenser pressures for comfort or commercial refrigeration conditions.

Given Data / Assumptions:

• Ambient condenser conditions representative of moderate climates.
• Medium-temperature application (not deep-freeze).
• Single-stage, air-cooled condenser assumption.

Concept / Approach:Condenser pressure corresponds to saturation pressure at typical condensing temperatures (say 35–45°C). For R-12 in this range, saturation pressures are commonly around 7–9 bar absolute. Evaporator pressures for above-zero evaporating temperatures are much lower (often 2–3 bar range), but the question focuses on condenser pressure.

Step-by-Step Solution:

Verification / Alternative check:Manufacturer pressure–temperature charts for R-12 corroborate that around 40°C the pressure is approximately 8 bar absolute.

Why Other Options Are Wrong:

2 bar: more typical of evaporator side at mild evaporating temperatures.15 or 30 bar: far above standard R-12 condenser pressures; these are more aligned with high-pressure refrigerants or transcritical CO2 systems.0.8 bar: vacuum operation is not a normal condenser condition.

Common Pitfalls:Confusing gauge with absolute pressure and forgetting temperature dependence; always cross-check with actual ambient and heat-rejection mode.

Final Answer:

8 bar