CA C-20 HVAC key terms

A room-by-room estimate of the heat a building gains and loses at design conditions, based on insulation, windows, occupancy, and outdoor temperature. Contractors use it to choose equipment size and to plan ductwork.

A counted list of materials taken from the plans - feet of duct, number of fittings, pipe and refrigerant line lengths, and equipment - used to price labor and material for a bid.

An accepted residential duct design method that matches the blower's available static pressure to the friction loss of the longest run plus its fittings, so every outlet receives its design airflow.

The resistance of an elbow, tee, or transition expressed as the length of straight duct that would cause the same pressure drop. It is added to measured length when sizing a run.

The outward push of air against duct walls, measured in inches of water column. Supply and return readings across a fan show how hard the blower is working against the system.

A sheet metal or factory-built chamber connected to the supply or return side of an air handler. Supply plenums split airflow into branch ducts; return plenums gather air from several grilles.

Adjusting volume dampers, registers, and fan speed until measured airflow at each outlet matches the design quantities, confirming the installed duct system performs as the load and duct design assumed.

The number of degrees by which a refrigerant vapor is warmer than its saturation temperature at the same pressure. Technicians use it to judge whether the evaporator is getting the correct refrigerant flow.

The number of degrees by which a liquid refrigerant is cooler than its saturation temperature at the same pressure. Measured at the condenser outlet, it indicates how much liquid refrigerant is backed up in the condenser.

The temperature at which a refrigerant changes between liquid and vapor at a given pressure. Because it moves with pressure, a gauge reading can be converted to a temperature on a pressure-temperature chart.

Heat added to or removed from a substance that changes its temperature but not its state, such as air warming as it crosses a heat exchanger.

Heat absorbed or released when a substance changes state at constant temperature, such as refrigerant boiling in an evaporator or water vapor condensing on a cold coil.

A modulating metering device that regulates refrigerant flow into the evaporator by balancing a sensing bulb, evaporator pressure, and a spring, holding superheat nearly constant as the load changes.

A four-way solenoid valve that redirects compressor discharge and suction gas so the indoor and outdoor coils swap roles, letting a heat pump heat or cool.

The outdoor temperature at which heat pump capacity equals the building's heat loss. Below that temperature the heat pump cannot keep up and supplemental heat must make up the difference.

Supplemental electric resistance or gas heat that operates along with the heat pump when outdoor air falls below the balance point or while the unit is in defrost.

A control-initiated period in which a heat pump melts frost from the outdoor coil, usually by temporarily reversing to cooling mode while the outdoor fan stops or slows.

The ratio of heating or cooling delivered to the energy consumed, expressed in matching units. A COP of 3 means three units of heat move for each unit of electricity used.

Air provided to a gas appliance for burning fuel and for diluting flue gases. Codes require permanent openings or ducts sized to the appliance input rating, and louvers must stay clear.

A relay with a low-voltage coil and heavy line-voltage contacts that switches power to a compressor, fan motor, or heater bank when the thermostat or control board calls.

A capacitor connected continuously in the circuit of a permanent split capacitor motor, shifting current in the start winding to improve running torque and efficiency.

A large-microfarad capacitor switched into the circuit only during motor startup to increase starting torque, then removed by a relay once the motor approaches operating speed.

The current a motor draws when its rotor cannot turn. Comparing a measured reading to the nameplate value helps identify a seized compressor or a failed start component.

A voltage-sensing relay whose coil is wired across the compressor start winding; rising back EMF as the motor speeds up opens the contacts and removes the start capacitor.

A time-delay control that energizes electric resistance heating elements one at a time and delays the blower, limiting the current surge and clearing residual heat at shutdown.

A small adjustable heater inside a mechanical thermostat that warms the bimetal element so its contacts open slightly before the room reaches setpoint, reducing temperature overshoot.

The fixed relationship in which voltage equals current multiplied by resistance. Technicians use it to predict expected amp and ohm readings when troubleshooting motors and control circuits.

A slow flow of dry nitrogen through piping while it is being brazed, which displaces oxygen and prevents black oxide scale from forming inside the tubing.

Joining copper tubing with a filler alloy that melts above 840 degrees F but below the melting point of the base metal; capillary action draws filler into a cleaned, properly heated joint.

A connection made by swaging the end of soft copper into a cone that seals against a matching seat on a brass fitting, common on mini-splits and some residential line sets.

Transferring refrigerant from a system into a recovery cylinder instead of venting it to the atmosphere, as federal rules require, so it can be reused, recycled, or reclaimed.

A unit of length equal to one thousandth of a millimeter, used on vacuum gauges. A reading of 500 microns or lower that holds steady shows a dry, leak-free system.

Closing the valve to the vacuum pump after evacuation and watching the micron gauge; a slow rise suggests moisture boiling off, while a fast rise points to a leak.

Charging refrigerant by weight on a scale using the nameplate charge plus allowances for line-set length; it is the most accurate method for fixed-orifice systems.

Locating refrigerant loss with electronic detectors, fluorescent dye, nitrogen pressure tests, or soap bubbles, performed before recharging so the repair is not wasted.

Scheduled service such as coil cleaning, belt and bearing checks, filter changes, electrical measurements, and charge verification that keeps equipment efficient and prevents breakdowns.

A safety procedure in which the disconnect is opened, locked, and tagged by the person working on the equipment so power cannot be restored unexpectedly while work is underway.

The state-adopted mechanical code governing HVAC installation in California, including equipment clearances, ventilation, combustion air, and venting requirements for permitted work.