RRB ALP Mechanic RAC Trade — Solved Practice Question Bank

Q: List the four main components of a basic vapor-compression refrigeration cycle in order. Sol: Compressor → Condenser → Expansion device → Evaporator (then back to compressor, repeating the cycle). Q: Why must only vapor (not liquid) enter the compressor? Sol: Liquid refrigerant entering a compressor cannot be compressed like a gas and can cause "liquid slugging" — serious mechanical damage to the compressor's pistons/valves. Q: What does "1 Ton of Refrigeration" represent as a cooling capacity unit? Sol: Approximately 3.5 kW of cooling capacity — historically defined as the cooling effect of melting one ton of ice in 24 hours.

Q: Why were CFC refrigerants like R-12 banned? Sol: They deplete the stratospheric ozone layer, which protects Earth from harmful UV radiation. Q: What is a common cause of an evaporator coil icing up? Sol: Low refrigerant charge, restricted airflow (dirty filter/blocked fins), or a faulty expansion device — all of which push evaporator temperature too low. Q: What commonly causes high discharge pressure at the compressor? Sol: A dirty/blocked condenser (poor heat rejection), refrigerant overcharge, or trapped non-condensable gases (air) in the system.