ITI/NCVT RAC Mechanic (AITT Theory) study guide
ITI/NCVT RAC Mechanic (AITT Theory) · Work through your exam, one topic at a time.
The ITI/NCVT RAC Mechanic (AITT Theory) is the All India Trade Test theory paper for candidates who have completed the Refrigeration and Air Conditioning Mechanic trade under the Craftsman Training Scheme. It is conducted by the National Council for Vocational Training (NCVT) and is one of the requirements for the National Trade Certificate. The ITI/NCVT RAC Mechanic (AITT Theory) study guide has 10 sections and about 3,668 words.
01Trade safety, hand tools, measuring instruments and workshop practice
AITT questions here are practical: which extinguisher for a live electrical fire, how to store an R290 cylinder, which tool deburrs a copper tube, and what a vernier actually reads. These marks are easy to secure and easy to lose through careless wording.
342 words, about 2 min02Basic electricity, electrical measuring instruments and control devices
Ohm's law, power and power factor, single- and three-phase supply, insulation and earth testing, and the selection and function of MCB, RCCB/ELCB, overload relay, thermostat, pressure switch and solenoid valve. V = IR; P = VI = I²R; single phase P = VI cos phi; three phase P = √3 x V x I x cos phi.
373 words, about 2 min03Thermodynamics, heat, temperature, pressure and psychrometry fundamentals
Heat, temperature and pressure fundamentals plus psychrometry: unit conversions, sensible and latent heat, absolute versus gauge pressure, vacuum measurement, dry-bulb, wet-bulb and dew-point temperature, relative humidity, enthalpy and the comfort zone. 1 kcal = 4.187 kJ; 1 TR = 3.517 kW = 3024 kcal/h = 12 000 Btu/h; 1 bar = 14.5 psi = 100 kPa; 1 kW = 860 kcal/h.
377 words, about 2 min04Refrigeration principles, vapour compression cycle and system components
The vapour compression cycle: why refrigeration needs work input, the four processes, reading the P-h diagram, COP, superheat, subcooling, compression ratio and the meaning of one tonne of refrigeration. Heat flows only from hot to cold.
341 words, about 2 min05Refrigerants, lubricants, their properties, handling and environmental regulations
Refrigerant properties and selection, safety groups, ODP and GWP, Indian and international regulation, recovery practice, and the lubricants with their matching rules. Key properties: boiling point at atmospheric pressure (R134a −26 °C, R22 −41 °C, R410A −51 °C, R717 −33 °C, R600a −12 °C), critical temperature (R134a 101 °C, R410A about 71 °C, R744 31 °C), latent heat, oil miscibility, dielectric strength, toxicity and flammability.
384 words, about 2 min06Compressors, condensers, evaporators, expansion devices and accessories
Construction and selection of compressors, condensers, evaporators, expansion devices and line accessories, and diagnosing their performance from pressures, temperatures, superheat and subcooling. Compressors: reciprocating (hermetic, semi-hermetic, open belt), rotary vane for small room units, scroll for splits and VRF, screw and centrifugal for large plants.
351 words, about 2 min07Domestic and commercial refrigeration appliances: refrigerators, deep freezers, water coolers, bottle coolers, visi coolers
Circuit and control layout of domestic and frost-free refrigerators, chest and upright deep freezers, water coolers, bottle coolers and visi coolers, plus typical faults and their symptoms. Domestic refrigerator: hermetic compressor (commonly R600a, charge 150 g or less), capillary tube, wire-and-tube or roll-bond evaporator, thermostat, PTC or current relay, run capacitor, door gasket, anti-sweat pipe in the frame.
368 words, about 2 min08Air conditioning systems: window, split, cassette, ductable, package and central plants
Selection and layout of window, split, cassette, ductable, package and central chilled-water systems: components, airflow, psychrometric processes and control arrangements. Window AC: self-contained, room air cools the condenser, usually fixed speed.
354 words, about 2 min09Installation, commissioning, servicing, troubleshooting and preventive maintenance
Site preparation, pipe work, pressure testing, evacuation, charging, commissioning checks and the systematic servicing, troubleshooting and preventive-maintenance routine expected in the trade. Pipe work: cut with a tube cutter, deburr, anneal before bending, keep bends reasonable, insulate the suction line and fit a liquid line filter-drier.
367 words, about 2 min10Electrical controls, motors, starters, wiring diagrams and PCB/electronic controls
Compressor motors and their starting circuits, capacitors, relays, overload and safety controls, starters, wiring diagrams and the electronic controls (PCBs, thermistors, inverters) used in modern air conditioners. Single-phase compressor circuits: PSC (run capacitor only), CSR (current relay with start capacitor), CSCR (potential relay with start and run capacitors), and split-phase with centrifugal switch.
411 words, about 2 min