Glossary · 54 terms
HVAC/R terms for the 313A exam
Plain definitions of the terms that show up in refrigeration and air conditioning exam questions, each linked to related terms and to deeper articles.
0–9
A
- A2L refrigerantA refrigerant classed as lower toxicity (A) and lower flammability (2L).
- Azeotropic blendA refrigerant mixture that boils and condenses like a single substance, with no glide.
C
- Certificate of Qualification (C of Q)The certificate Skilled Trades Ontario issues after a candidate passes the certifying exam for a trade.
- CommissioningStarting up a new or retrofitted system, verifying its performance and recording a baseline.
- Compressor burnoutA motor failure that overheats the windings and leaves acid and carbon in the system.
- Compressor windings (common, start, run)The three terminals of a single-phase compressor motor, identified by resistance.
- CondenserThe heat exchanger where hot refrigerant vapour gives up heat and condenses to liquid.
- ContactorA relay rated for motor loads that connects line voltage to the compressor and condenser fan.
- Crankcase heaterA heater that keeps compressor oil warm so refrigerant does not migrate into it during the off cycle.
D
- Defrost cycleA timed or demand-initiated period that melts frost from an evaporator coil.
- Dew point and bubble pointFor a blend, the saturation temperatures at which the last liquid boils (dew) and the first vapour forms (bubble).
E
- Electronic expansion valve (EEV)A motor-driven metering valve positioned by a controller using temperature and pressure sensors.
- EvacuationPulling a deep vacuum on a system to remove air, moisture and non-condensables before charging.
- EvaporatorThe heat exchanger where refrigerant boils and absorbs heat from the space or product being cooled.
- External static pressureThe resistance to airflow a blower works against outside its own cabinet.
F
- Federal Halocarbon Regulations, 2022Canada's federal rules on releasing, recovering, leak testing and charging halocarbons for systems under federal jurisdiction.
- Filter drierA replaceable core that removes moisture, acid and debris from the refrigerant.
- Fixed orificeA metering device with a fixed opening, such as a piston or capillary tube.
- FloodbackLiquid refrigerant returning to the compressor during operation.
- FractionationWhen a zeotropic blend separates because one component evaporates faster than the others.
G
H
- HalocarbonIn Canadian federal regulation, a substance listed in Schedule 1 of the Federal Halocarbon Regulations, 2022, alone or in a mixture.
- Holding chargeDry nitrogen left in new piping or equipment to keep moisture out and reveal leaks.
L
- Latent heatHeat that changes a substance's state (boiling or condensing) without changing its temperature.
- Leak testChecking a refrigeration circuit for leaks, usually by pressurizing with dry nitrogen.
- Liquid lineThe refrigerant line from the condenser outlet to the metering device.
- Lockout/tagoutIsolating energy sources with personal locks and tags, then verifying isolation before work.
M
- Major Work Activity (MWA)One of the top-level blocks of a Red Seal occupational standard, each with a share of the exam.
- Metering deviceThe component that drops refrigerant from high-side to low-side pressure and controls flow into the evaporator.
- Micron (vacuum)One thousandth of a millimetre of mercury, the unit used to measure deep vacuum.
N
O
- Oil returnGetting compressor oil that circulates with the refrigerant back to the compressor.
- OverchargeMore refrigerant in a system than it was designed for.
- Ozone depletion potential (ODP)How much a substance damages stratospheric ozone relative to CFC-11.
P
- POE oilA synthetic ester lubricant used with most HFC and HFO refrigerants.
- Pressure-enthalpy diagramA chart of refrigerant pressure against heat content on which a refrigeration cycle can be drawn.
- Pressure-temperature chartA table giving each refrigerant's saturation temperature at each pressure.
R
- Recovery cylinderA refillable cylinder designed to hold recovered refrigerant, filled to no more than about 80% of capacity.
- Red SealThe Canadian program that sets common standards and exams for designated trades across provinces and territories.
- Refrigerant recoveryRemoving refrigerant from a system into a container instead of releasing it.
- Reversing valveThe four-way valve that swaps a heat pump between heating and cooling.
- Run capacitorA capacitor that stays in a single-phase motor circuit to improve running torque and efficiency.
S
- Saturation temperatureThe temperature at which a refrigerant boils or condenses at a given pressure.
- Scroll compressorA compressor that squeezes vapour between a fixed and an orbiting spiral.
- SubcoolingHow far a liquid's temperature is below its saturation (condensing) temperature at the same pressure.
- Suction lineThe refrigerant line carrying low-pressure vapour from the evaporator back to the compressor.
- SuperheatHow far a vapour's temperature is above its saturation temperature at the same pressure.
T
- Temperature glideThe change in saturation temperature as a zeotropic blend boils or condenses at constant pressure.
- Temperature splitThe drop in air temperature across an evaporator coil (return minus supply).
- Thermostat terminals (R, C, Y, G, W, O/B)The common letter conventions for 24 V control wiring between a thermostat and equipment.
- Thermostatic expansion valve (TXV)A metering device that adjusts refrigerant flow to hold evaporator superheat roughly constant.
V
Z