RRB ALP Refrigeration & AC Mechanic Syllabus

The RRB ALP CBT 2 Part B -- Refrigeration and AC Mechanic trade syllabus covers the core technical knowledge tested in the 75-question, 60-minute trade-specific section of the RRB ALP 2027 examination. Part B is qualifying in nature only: candidates must score a minimum of 35% (26.25 marks out of 75) to clear Part B. The marks scored in Part B are NOT added to the final merit list. Merit is determined entirely by CBT 2 Part A scores. The syllabus for Part B is based on the NCVT (National Council for Vocational Training) ITI curriculum for the Refrigeration and AC Mechanic trade at the ITI certificate level.

Quick Facts: ALP Refrigeration and AC Mechanic Trade

Important Note on Part B

CBT 2 Part B is qualifying only. A candidate who scores below 35% in Part B is eliminated regardless of their Part A score. However, a candidate who clears the 35% threshold in Part B is ranked exclusively on their CBT 2 Part A score. This makes Part B preparation essential for elimination prevention, while Part A preparation determines the final rank. Candidates should ensure they are thoroughly familiar with the Refrigeration and AC Mechanic trade theory and practical knowledge at the ITI level before the examination.

Detailed Refrigeration and AC Mechanic Trade Syllabus (Part B)

The Refrigeration and AC Mechanic trade syllabus for RRB ALP CBT 2 Part B is drawn from the NCVT ITI curriculum and tests trade theory, applied knowledge, and practical understanding across the following topic areas:

1. Fundamentals of Refrigeration and Thermodynamics

•        Thermodynamic Concepts: system; properties (temperature, pressure, enthalpy, entropy); laws of thermodynamics; Kelvin and Celsius scales

•        Refrigeration Effect: unit of refrigeration (TR -- ton of refrigeration = 3.5 kW = 12,000 BTU/hr); refrigerating effect; coefficient of performance (COP)

•        Refrigeration Methods: vapour compression; vapour absorption; thermoelectric; air cycle; Peltier effect

•        Vapour Compression Refrigeration Cycle (VCRC): components (compressor, condenser, expansion device, evaporator); T-S and P-H diagrams; sub-cooling; superheating; COP calculation

•        Mollier Chart (P-H Diagram): reading; plotting of VCRC; finding COP; compressor work; refrigerating effect; condenser load

2. Refrigerants

•        Classification: halocarbon (CFC, HCFC, HFC, HFO); hydrocarbon; inorganic (ammonia R717, CO2 R744, water R718)

•        Properties: boiling point; freezing point; latent heat; critical temperature and pressure; ODP (Ozone Depletion Potential); GWP (Global Warming Potential); flammability; toxicity; ASHRAE 34 safety classification

•        Common Refrigerants: R22 (phase-out); R134a (automotive); R410A (air conditioning); R32; R404A (cold storage); R407C; R600a (isobutane); R290 (propane); R717 (ammonia -- industrial)

•        Montreal Protocol: substances controlled; phase-out schedule; alternatives to ODS; HFO refrigerants (R1234yf, R1234ze)

•        Refrigerant Handling: recovery; recycling; reclaiming; leak detection; charging procedures; cylinders (colour coding)

3. Compressors

•        Types: reciprocating (hermetic, semi-hermetic, open type); rotary (rolling piston, vane); scroll; screw (twin screw, single screw); centrifugal; oil-free

•        Reciprocating Compressor: construction (piston, cylinder, crank, con-rod, valve plate, crankcase); volumetric efficiency; clearance ratio; re-expansion; compression ratio

•        Hermetic Compressor: sealed unit; motor-compressor; starting and running windings; PTC thermistor; current relay; overload protector

•        Scroll Compressor: working principle; advantages; limitations; orbit; discharge port

•        Compressor Performance: suction and discharge temperatures and pressures; superheat at suction; compression efficiency; power input

•        Compressor Maintenance: oil level; oil type; suction and discharge pressure; current draw; cylinder head temperature; oil change; valve servicing

4. Condensers and Evaporators

•        Condensers: air cooled (forced draft, natural draft); water cooled (shell and tube, shell and coil, double pipe, evaporative condenser); tube types; fin design; subcooling; condenser duty

•        Cooling Towers: induced draft; forced draft; counterflow; crossflow; approach temperature; range; make-up water; blowdown; Legionella prevention

•        Evaporators: direct expansion (DX) and flooded types; dry expansion coil; fan coil unit; shell and tube; tube-in-tube; plate heat exchanger; fin-and-tube coil; evaporator load; superheat

•        Frost and Defrost: types of defrost (electric, hot gas, air, water); defrost cycle; defrost controls (time-clock, temperature, adaptive)

5. Expansion Devices and Controls

•        Expansion Devices: capillary tube (sizing; applications; advantages and disadvantages); thermostatic expansion valve (TXV -- bulb location; superheat setting; external equaliser; hunting); automatic expansion valve (AXV); float valve; electronic expansion valve (EEV)

•        Refrigeration Controls: thermostat; pressostat (HP and LP); oil differential pressure switch; defrost thermostat; solenoid valve; check valve; filter drier; sight glass; suction accumulator; receiver

•        Refrigerant Flow Components: receiver; filter drier (bead type, solid core, block type); sight glass and moisture indicator; solenoid valve; check valve; suction accumulator; oil separator; liquid distributor

6. Air Conditioning Systems

•        Window AC: components (indoor and outdoor sections); hermetic compressor; capillary tube; axial fan; cross-flow fan; air filter; thermostat; modes (cool, fan, dry); seasonal maintenance

•        Split AC: indoor unit types (wall-mounted, floor-mounted, cassette, duct); outdoor unit; connecting pipes (liquid and suction lines); electrical connections; refrigerant charging; commissioning; fault finding

•        Multi-Split and VRF/VRV Systems: variable refrigerant flow; inverter compressor; branch controller; refrigerant piping sizing; multiple indoor units; zone control

•        Psychrometrics: dry bulb temperature (DBT); wet bulb temperature (WBT); dew point temperature; specific humidity; relative humidity; enthalpy; psychrometric chart; processes (sensible heating/cooling; humidification; dehumidification; mixing)

•        Air Handling Unit (AHU): components (fan, coil, filter, humidifier, heating coil); AHRI ratings; AAOP; SHR

•        Railway Coach Air Conditioning: RMPU (Roof Mounted Package Unit); pre-cooling; capacity; refrigerant; electrical supply; maintenance schedule for Indian Railways coaches; HVAC testing

•        Centralized Chilled Water AC: chiller types (air-cooled, water-cooled, absorption); chilled water temperature; condenser water; cooling tower; AHU; FCU; chilled water piping

7. Commercial Refrigeration

•        Reach-in and Walk-in Coolers and Freezers: construction; panel assembly; floor insulation; door types (strip curtain, glass, solid); refrigeration system; temperature range

•        Display Cases: open and closed; condensing unit; case rating; defrost schedule

•        Ice Making Machines: tube ice; flake ice; cube ice; plate ice; working cycle; capacity

•        Cold Storage: design considerations; insulation; vapour barrier; refrigeration load calculation; temperature and humidity requirements; product storage guidelines

8. Electrical and Controls for Refrigeration

•        Electrical Components: capacitors (start and run); relays (current relay, PTC relay, potential relay); overload protector; hermetic motor (RSIR, CSIR, RSR, CSR, PSC, CSCR -- types and applications)

•        Wiring Diagrams: reading ladder diagrams for AC and refrigeration systems; identify and trace circuits

•        Troubleshooting: systematic fault diagnosis; manifold gauge set readings; temperature measurement; subcooling and superheat checks; electrical tests; refrigerant leak detection (electronic detector, UV dye, soap bubble)

•        Tools: manifold gauge set; vacuum pump; leak detector; refrigerant recovery machine; flaring tool; swaging tool; tube bender; charging cylinder

9. Safety

•        Refrigerant Safety: handling; cylinder storage; PPE (gloves, goggles, apron); asphyxiation risk; first aid for refrigerant exposure

•        Electrical Safety: working on live AC equipment; capacitor discharge; insulation testing; LOTO

•        Mechanical Safety: pressure vessel regulations; safety valves; refrigerant system pressure testing; IS 659

Weightage Analysis and Preparation Strategy

The 75 Part B questions are drawn proportionally from across all major topic areas of the Refrigeration and AC Mechanic trade curriculum. Questions test both theoretical knowledge (principles, formulae, definitions, standards, safety rules) and applied understanding (fault diagnosis, calculations, material selection, tool usage, quality checks). The following approach maximises Part B preparation efficiency:

•        Revise systematically from NCVT ITI Refrigeration and AC Mechanic trade theory textbooks for Semester 1 and Semester 2

•        Focus on definitions, formulae, standards (BIS/IS codes), safety regulations, and technical specifications -- these are directly testable as MCQs

•        Practise numerical calculations relevant to the trade (e.g., circuit calculations for Electrician, speed/feed calculations for Fitter/Turner/Machinist)

•        Study common faults, their causes, symptoms, and remedies for all major equipment in the trade

•        Revise tools, instruments, and equipment used in the trade: their names, specifications, uses, and maintenance

•        Solve previous years' RRB ALP Part B question banks for your specific trade

•        Allocate 60 minutes of daily trade-specific study alongside Part A preparation throughout the preparation period

Frequently Asked Questions

Q1. Is CBT 2 Part B merit-based or qualifying?

CBT 2 Part B is qualifying only. A minimum score of 35% is required to pass Part B. The marks scored in Part B are not added to the merit list. Only Part A marks determine the final ranking.

Q2. What happens if a candidate fails Part B?

Candidates who score below 35% in Part B are disqualified regardless of their Part A performance. They will not be considered for Document Verification or further selection stages.

Q3. How should I divide study time between Part A and Part B?

Since Part A determines the final merit and Part B is qualifying, prioritise Part A in your preparation. However, allocate at least 30 to 40% of study time to Part B to ensure you comfortably clear the 35% qualifying threshold. Aiming for 50 to 55 marks (about 70%) in Part B provides a safe buffer.

Q4. Is the Part B syllabus the same as the ITI exam syllabus?

Yes. The RRB ALP Part B syllabus is directly based on the NCVT ITI curriculum for the relevant trade. Candidates who have completed their ITI in the relevant trade and revised their course material systematically are well positioned for Part B.