KY HVAC flashcards
KY HVAC · Build recall with a focused review session.
32 cards. Read the term and the definition here. The deck at the top of this page is optional.
- Superheat
- The difference between actual suction-line temperature and saturated suction temperature at the same pressure; it shows evaporator metering and charge condition.
- Subcooling
- The difference between saturated condensing temperature and liquid-line temperature; it confirms a liquid seal and proper charge at the condenser outlet.
- Compression ratio
- Absolute discharge pressure divided by absolute suction pressure; high ratios increase discharge temperature and reduce compressor volumetric efficiency.
- TXV
- A thermostatic expansion valve modulates refrigerant flow to maintain a set evaporator superheat as load and conditions change.
- R-410A charging
- R-410A is a near-azeotropic blend, so it must be charged as a liquid from the cylinder to prevent refrigerant fractionation.
- Micron vacuum
- A vacuum measured in microns; a standing decay test verifies the system is leak-free and dehydrated before charging.
- Complete combustion
- A chemical reaction in which carbon in fuel combines with oxygen to form carbon dioxide, with sufficient air and proper venting preventing carbon monoxide.
- Manifold pressure
- Gas pressure measured at the burner orifices; typical values are about 3.5 in. w.c. for natural gas and 10 in. w.c. for LP.
- Limit switch
- A temperature-activated safety that opens the burner circuit when plenum or heat-exchanger temperature exceeds its setpoint.
- Flame rollout switch
- A manual-reset safety that trips when flame burns outside the heat exchanger, often caused by a blocked flue or overfiring.
- Combustion analyzer
- An instrument that measures oxygen, carbon dioxide, carbon monoxide, and flue temperature to calculate efficiency and verify safe combustion.
- Sensible heat equation
- Air sensible heat in Btu/h equals 1.08 times standard-air CFM times the dry-bulb temperature difference.
- Total heat equation
- Air total heat in Btu/h equals 4.5 times standard-air CFM times the enthalpy difference between entering and leaving air.
- Equal friction method
- A duct sizing method that selects duct sizes so friction loss per unit length is approximately equal in each branch.
- External static pressure
- The sum of supply and return static pressures the blower must overcome; it is compared with the fan performance table.
- MERV
- Minimum Efficiency Reporting Value rates a filter's particle capture; higher ratings capture more particles but usually add pressure drop.
- ASHRAE 62.2
- A residential ventilation standard; its whole-house rate is about 3 CFM per 100 square feet plus 7.5 CFM per bedroom factor.
- Ohm's law
- Voltage equals current times resistance; for AC single-phase power, watts equal volts times amps times power factor.
- Locked rotor amps
- The current a motor draws at standstill; it is much higher than running amps and is used for protection and conductor sizing.
- Run capacitor
- A capacitor that remains in the motor circuit during normal operation to improve phase angle and running torque.
- Potential relay
- A relay that removes the start capacitor from the circuit when motor back-EMF voltage rises after startup.
- 24-volt control circuit
- A low-voltage circuit powered by a transformer that operates thermostats, contactors, relays, and gas valves.
- Manual J
- An ACCA method for calculating residential heating and cooling loads from envelope, infiltration, internal gains, and solar effects.
- Manual S
- An ACCA method for selecting equipment capacity using Manual J loads and manufacturer performance data at design conditions.
- Manual D
- An ACCA method for sizing duct systems using room airflows, available static pressure, and friction rate.
- Sensible heat ratio
- Sensible load divided by total load; it indicates how much cooling capacity removes heat versus moisture.
- U-factor
- The overall heat transfer coefficient, equal to 1 divided by R-value, used in Q = U times A times temperature difference.
- HVAC permit
- A local authorization required before installing or altering HVAC systems; it triggers inspections for code compliance.
- EPA Section 608
- A federal rule requiring certification for technicians who service refrigerant-containing appliances and prohibiting intentional refrigerant venting.
- Kentucky HVAC license
- A state credential issued through the Kentucky Department of Housing, Buildings and Construction for HVAC contractors.
- Mechanic's lien
- A legal claim against property for unpaid labor or materials; notice and filing deadlines vary by state law.
- Change order
- A written modification to a contract's scope, price, or schedule that is signed before the extra work proceeds.