HVAC Excellence Master HP key terms

The temperature of refrigerant vapor above its saturation temperature at a given pressure. Measured at the evaporator outlet, it confirms the coil is fully fed with liquid and protects the compressor from floodback.

The temperature of liquid refrigerant below its saturation temperature at a given pressure. Measured at the condenser outlet, it indicates how much liquid is stacked in the condenser and whether the metering device is properly fed.

The temperature at which a refrigerant changes phase at a given pressure. On a pressure-temperature chart, it links gauge pressure to coil temperature and is the reference point for superheat and subcooling calculations.

A table or graph relating refrigerant pressure to its boiling and condensing temperature. Technicians use it to convert gauge readings into saturation temperatures when calculating superheat, subcooling, and evaporator or condenser performance.

A thermostatic expansion valve that meters liquid refrigerant into the evaporator by balancing refrigerant pressure, bulb pressure, and spring force. It maintains a set superheat at the evaporator outlet across changing loads.

A line on a thermostatic expansion valve that routes evaporator outlet pressure to the underside of the diaphragm. It compensates for pressure drop through the distributor and coil so superheat control stays accurate.

The indoor coil where low-pressure liquid refrigerant absorbs heat from air or water and boils to vapor. Its performance sets supply-air temperature, latent capacity, and the superheat seen at the compressor suction.

The outdoor coil where high-pressure refrigerant vapor rejects heat to outdoor air or water and condenses to liquid. Condensing temperature, cleanliness, and airflow determine head pressure and system efficiency.

The saturation temperature at which refrigerant vapor turns to liquid in the condenser at the existing head pressure. Comparing it to outdoor ambient reveals condenser approach and airflow or fouling problems.

The discharge pressure measured at the compressor outlet, corresponding to condensing temperature. High head pressure raises compression ratio and power draw; low head pressure can starve the metering device and impair oil return.

Discharge absolute pressure divided by suction absolute pressure. Ratios above roughly 10:1 on many compressors signal overheating, poor capacity, and shortened compressor life, often from high condensing or low suction pressure.

The temperature difference between return air entering the evaporator and supply air leaving it. It verifies airflow and charge; an abnormally low or high split points to airflow, charge, or duct problems.

The volume of air moved through the system, usually stated in cubic feet per minute. Correct airflow is required for rated capacity, proper superheat and subcooling, and reliable compressor cooling.

The resistance to airflow in a duct system, measured in inches of water column. High external static pressure reduces airflow and capacity, so it is checked when diagnosing low delta T or frozen coils.

The current seasonal energy efficiency ratio metric for central air conditioners, tested under revised external static pressure conditions. Higher ratings mean lower estimated seasonal energy use for cooling.

The current heating seasonal performance factor metric for heat pumps, reflecting revised test conditions. It estimates seasonal heating efficiency and appears on the equipment energy guide label.

The outdoor temperature at which a heat pump's heating capacity equals the building's heat loss. Below it, supplemental heat must run to maintain indoor temperature.

Supplemental electric resistance or other heat that energizes when a heat pump cannot meet load, such as below the balance point or during defrost. It raises power demand sharply and should be staged carefully.

A control sequence that temporarily reverses or stops a heat pump to melt frost from the outdoor coil. It uses sensors, timers, and often auxiliary heat to prevent cold blow during the cycle.

A four-way solenoid valve that swaps suction and discharge connections to change a heat pump between heating and cooling. Failure leaves the system stuck in one mode or causes poor capacity.

The EPA regulation under the Clean Air Act governing refrigerant handling, recovery, recycling, and reclamation. Certification is required to service appliances, and knowing its requirements is essential for legal compliance.

Removing refrigerant from a system into an approved container without processing it. Required before opening a circuit or disposing of equipment, and recovered refrigerant must be handled per EPA rules.

Cleaning recovered refrigerant for reuse in the same owner's equipment by removing oil, moisture, and particulates. It does not restore refrigerant to purity standards required for resale or different equipment.

Processing used refrigerant to new-product purity specifications, typically by an EPA-certified reclaimer. Reclaimed refrigerant may be sold and used in any compatible equipment, unlike recycled refrigerant.

Pulling a vacuum on a sealed system to remove air and moisture before charging. Proper evacuation to a deep micron level prevents acid formation, ice blockage, and premature compressor failure.

An instrument that measures very low absolute pressure in microns during evacuation. It confirms the system holds a deep vacuum and that no moisture or leaks remain before charging.

Flowing dry nitrogen through a system while brazing to displace oxygen and prevent internal oxidation. It is also used for pressure testing, since nitrogen is inert and does not add moisture.

The percentage of refrigerant charge lost per year, used to trigger repair requirements under EPA rules. Exceeding the applicable threshold for an appliance type requires repair within set timeframes.

A mildly flammable refrigerant classification with low burning velocity. Systems using A2L refrigerants require specific handling, ventilation, and ignition-source precautions during service and installation.

The amount of refrigerant in a system, set by weight or by superheat and subcooling targets. Correct charge is required for capacity, efficiency, and compressor reliability.

An electrically controlled switch that closes high-current circuits for compressors and fans using a low-voltage coil. Pitted contacts, burned coils, and loose lugs are common causes of no-cool calls.

A component that stores electrical energy to start or run motors and to smooth control voltage. A weak or bulged run capacitor causes hard starts, overheating, and low motor torque.

A start capacitor and potential relay added to boost compressor starting torque. It is used on systems with high compression ratios, low voltage, or long line sets to prevent locked-rotor trips.

The printed circuit assembly that sequences blower, compressor, reversing valve, and safety inputs. Diagnostic fault codes and LED blink patterns on it guide most modern troubleshooting.

The user and control device that senses space temperature and commands heating, cooling, and fan operation. Wiring, configuration, and sensor calibration errors cause many comfort complaints.

A control state that prevents equipment from running after repeated faults or unsafe conditions. It protects the compressor and forces a technician to diagnose the underlying cause.

The pump that raises refrigerant pressure and moves it through the circuit. It is the most expensive component and is protected by suction cooling, oil return, and electrical safeties.

The indoor fan that moves conditioned air through ducts and across the evaporator or heat exchanger. Its speed taps and wheel condition directly affect airflow, delta T, and capacity.