Odisha CHSE +2 VOC Field Technician Air Conditioner flashcards

33 cards. Read the term and the definition here. The deck at the top of this page is optional.

Tonn of refrigeration

A unit of cooling capacity equal to 3.517 kW or 210 kJ/min, defined as the heat absorbed to melt one short ton (907 kg) of ice in 24 hours.

COP of refrigerator

Coefficient of performance = refrigerating effect divided by compressor work input. For a Carnot cycle, COP = T_L / (T_H − T_L) with temperatures in kelvin.

Relative humidity

The ratio of the actual partial pressure of water vapour in air to the saturation pressure at the same dry-bulb temperature, expressed as a percentage.

Dew point temperature

The temperature at which air becomes saturated (RH = 100%) and water vapour begins to condense; cooling below dew point causes dehumidification.

Sensible vs latent heat

Sensible heat changes temperature without changing state (Q = m·c·ΔT); latent heat changes state at constant temperature (Q = m·h_fg).

R-410A composition

A near-azeotropic blend of 50% R-32 and 50% R-125 by mass, with zero ODP, GWP about 2088, and operating pressures roughly 1.6 times those of R-22.

ODP definition

Ozone Depletion Potential, a relative measure of how much a substance destroys stratospheric ozone, with CFC-11 assigned the reference value of 1.0.

GWP definition

Global Warming Potential, a relative measure of the heat trapped by a greenhouse gas over 100 years compared with carbon dioxide, which is assigned a value of 1.0.

R-22 phase-out

R-22 is an HCFC with ODP about 0.055; it is being phased out under the Montreal Protocol and is replaced by R-32, R-410A, or R-290 in new equipment.

POE oil

Polyolester synthetic lubricating oil, mandatory with HFC refrigerants such as R-134a and R-410A; it is hygroscopic and must be kept sealed from air.

Montreal Protocol

The 1987 international treaty that phases out ozone-depleting substances such as CFCs and HCFCs; its 2016 Kigali Amendment adds an HFC phase-down for climate protection.

Phosgene formation

A toxic gas produced when CFC or HCFC refrigerant contacts an open flame; therefore flame leak detectors must never be used on such systems.

Frostbite first aid

Refrigerant contact causes frostbite; flush the affected skin with lukewarm water, not hot water, cover loosely, and seek medical attention.

TXV function

A thermostatic expansion valve modulates refrigerant flow to maintain a constant evaporator superheat, typically 5–8 K, using bulb, evaporator, and spring pressures.

Capillary tube

A fixed-restriction expansion device made of a long small-bore tube, used in small window and split air conditioners; it cannot adjust to load changes.

Filter-drier

A device in the liquid line containing desiccant and a screen that removes moisture and solid particles, protecting the expansion device and compressor from blockage and corrosion.

Four-way reversing valve

A solenoid valve in a heat pump that reverses refrigerant flow direction, switching the system between cooling and heating modes by swapping evaporator and condenser roles.

Split AC indoor height

The indoor unit is mounted 2.3–2.5 m above the floor, with at least 15 cm clearance from the ceiling and side walls for proper air circulation.

Evacuation level

A deep vacuum of 500 microns (0.67 mbar) or lower must be reached and held for 10 minutes to confirm the system is dry and leak-free.

Nitrogen pressure test

A tightness test using dry nitrogen at 350–550 psi (24–38 bar) held for 24 hours; any pressure drop indicates a leak that must be repaired.

Flare nut torque

Standard tightening torques for flare joints: about 15–18 N·m for 1/4 inch, 35–40 N·m for 3/8 inch, and 50–55 N·m for 1/2 inch.

Superheat diagnosis

Superheat = suction temperature minus evaporating temperature. High superheat with low suction pressure indicates undercharge or a restriction; low superheat indicates overcharge.

Dirty condenser symptom

A dirty condenser raises discharge pressure and running current, raises suction pressure slightly, and reduces cooling capacity; clean the coil to restore performance.

Compressor winding test

Measure resistance between C–R, C–S, and R–S with a multimeter; C–R plus C–S should equal R–S. Infinite or zero readings indicate a faulty winding.

Capacitor replacement rule

After safely discharging, measure capacitance with a meter; replace the capacitor if the reading is more than 10% below the rated microfarad value.

PSC motor

Permanent split capacitor motor, the standard fan and small compressor motor in split air conditioners; it uses a run capacitor but no start capacitor.

Inverter AC control

An inverter air conditioner varies compressor speed using an IPM module and variable-frequency drive; check DC bus voltage and fault codes before replacing the PCB.

NTC thermistor

A negative-temperature-coefficient sensor whose resistance falls as temperature rises; a typical room thermistor reads about 10 kΩ at 25 °C.

Micron gauge

A vacuum instrument that measures absolute pressure in microns; it is essential to confirm deep vacuum because a manifold gauge cannot resolve low pressures.

Megger test

An insulation resistance test at 500 V DC between compressor winding and earth; a reading of at least 1 MΩ indicates acceptable insulation.

Manifold gauge colours

Blue hose connects to the low-pressure side, red to the high-pressure side, and yellow to the vacuum pump or charging cylinder.

LOTO procedure

Lock-out/tag-out: isolate the electrical supply, lock the breaker, attach a warning tag, and verify with a tester before beginning any service work.

Class C fire

A fire involving live electrical equipment; extinguish with CO2 or dry powder, never with water or foam, and isolate the supply first.