Red Seal Refrigeration & AC Mechanic flashcards

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

Ozone Depletion Potential

A relative number comparing a substance's ability to destroy stratospheric ozone, with CFC-11 set at 1.0. HCFCs such as R-22 have a value below 1.

Global Warming Potential

A relative measure of how much heat a greenhouse gas traps over 100 years compared with carbon dioxide, which is set at 1. R-410A is roughly 2088.

80% Cylinder Fill Rule

Refrigerant cylinders must never be filled beyond 80% of their capacity by liquid volume, leaving vapour space so liquid expansion with temperature does not rupture the cylinder.

Confined Space Atmospheric Testing

Before entry, test oxygen between 19.5 and 23 percent, flammability below 10 percent of the lower explosive limit, and toxicity, with a standby attendant outside.

Micron Gauge

An instrument measuring absolute pressure in microns, where one atmosphere is about 760,000 microns. It verifies evacuation depth and standing vacuum on a refrigeration system.

Standing Vacuum Test

After evacuating below 500 microns, isolate the pump and confirm the pressure rise stays small over about ten minutes, proving the system is dry and leak-free.

Nitrogen Purge While Brazing

A slow flow of dry nitrogen through the tubing during brazing displaces oxygen, preventing internal oxidation scale that would later clog driers, valves, and screens.

Clamp-On Ammeter

A meter whose jaws surround a conductor to measure current without breaking the circuit. It is used to check compressor, fan, and heater amp draw against nameplate values.

Ton of Refrigeration

A cooling rate equal to 12,000 Btu per hour, 200 Btu per minute, or 3.517 kilowatts, based on melting one ton of ice in 24 hours.

Superheat

The difference between the actual suction line temperature and the saturated evaporating temperature at the same pressure. It confirms the evaporator is fully fed with liquid.

Subcooling

The difference between the condensing temperature and the liquid line temperature. It confirms the condenser has enough liquid refrigerant and the charge is adequate.

Latent Heat

Heat added or removed that changes a substance's state without changing its temperature, such as boiling liquid refrigerant into vapour inside the evaporator coil.

Relative Humidity

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

Potential Relay

A start relay whose coil senses rising back-EMF across the start winding. It opens the start capacitor circuit once the motor reaches running speed.

PSC Motor

A permanent split capacitor motor with a run capacitor in series with the start winding. It has moderate starting torque and is common on fans and small compressors.

Thermistor

A solid-state temperature sensor whose resistance changes predictably with temperature, feeding a controller that interprets the resistance as a temperature reading.

Contactor

An electrically operated switch whose coil is energized by the control circuit, closing heavy-duty contacts that supply power to compressors, fans, or heaters.

ACR Copper Tubing

Copper tubing manufactured, cleaned, and capped for refrigeration service, sized by outside diameter, and kept sealed until installation to prevent moisture and dirt entry.

Brazing Versus Soldering

Brazing joins tubing with filler melting above 450 degrees Celsius and is required for refrigerant lines. Soldering melts below that and is unsuitable for system pressures.

Suction Line P-Trap

A trap installed at the bottom of a vertical suction riser to collect oil and return it to the compressor, preventing oil logging and loss of lubrication.

Filter Drier

A device in the liquid line containing desiccant and a screen that removes moisture and particles. The flow arrow must point in the direction of refrigerant flow.

POE Lubricant

Polyol ester oil used with HFC and HFO refrigerants. It is hygroscopic, so containers must stay sealed and systems must be evacuated thoroughly to avoid moisture.

Refrigerant Reclamation

Processing recovered refrigerant to meet AHRI 700 purity standards, performed by a certified reclaimer. Reclaimed refrigerant can be resold and reused in any system.

Near-Azeotropic Blend

A refrigerant mixture whose components have slightly different boiling points, causing temperature glide. R-410A must be charged as a liquid to prevent fractionation.

Recovery Versus Recycling

Recovery removes refrigerant from a system for storage. Recycling cleans it on site with oil separation and filtration but does not restore it to new specification.

Triple Evacuation

An evacuation method using three vacuum cycles separated by dry nitrogen breaks, used on systems suspected of containing moisture, to drive out water vapour.

Weigh-In Charging

Charging refrigerant by weight using a scale and the nameplate charge, the most accurate method, then verified by superheat or subcooling readings.

External Static Pressure

The resistance to airflow measured across the blower and duct system. It is compared with the fan performance curve to determine actual delivered airflow in CFM.

High Discharge Pressure Causes

Dirty or blocked condenser, high ambient temperature, non-condensable gases, overcharge, or restricted condenser airflow. Each raises head pressure and compressor current.

Low Suction Pressure Causes

Restricted liquid line or filter drier, undercharge, faulty expansion valve, iced evaporator, or low heat load. Diagnose by checking superheat and airflow.

Pump-Down Control

A liquid line solenoid valve closes on thermostat satisfaction while the compressor runs until low pressure is reached, storing refrigerant in the receiver and preventing migration.

Sensible Heat Ratio

The sensible heat divided by the total heat of a load or coil. Equipment selection must match the space ratio to control both temperature and humidity properly.