TX HVAC Contractor flashcards
TX HVAC Contractor · 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.
- Sensible heat ratio
- The ratio of sensible cooling capacity to total cooling capacity; total capacity is the sum of sensible and latent capacity.
- One ton of cooling
- A cooling rate of 12,000 Btu per hour, approximately the heat needed to melt one ton of ice in 24 hours.
- Evaporator superheat
- The number of degrees the suction vapor is above its saturation temperature at the evaporator outlet; measured with a gauge and thermometer.
- Subcooling
- The number of degrees the liquid refrigerant is below its saturation temperature at the condenser outlet; used to verify charge in TXV systems.
- Evaporator delta T
- The dry-bulb temperature difference between return air entering and supply air leaving the evaporator; typically 16 to 22 degrees Fahrenheit.
- Apparatus dew point
- The effective coil surface temperature at the air leaving condition; dehumidification occurs when this is below the entering air dew point.
- Furnace temperature rise
- The supply-air temperature minus return-air temperature across a furnace; calculated as output Btu/h divided by 1.08 times cfm.
- AFUE
- Annual Fuel Utilization Efficiency; the ratio of annual heat output to annual fuel energy input, expressed as a percentage for heating equipment.
- Heat pump balance point
- The outdoor temperature at which heat pump heating capacity equals the building heat loss; below this point supplemental heat is needed.
- Combustion air requirement
- Roughly 50 cubic feet of free space per 1,000 Btu/h of gas input for unconfined spaces; confined spaces need dedicated openings.
- Manifold pressure
- The gas pressure measured at the burner manifold; typically about 3.5 inches water column for natural gas and 10 to 11 for propane.
- Saturation temperature
- The temperature at which a refrigerant boils or condenses at a given pressure; superheat and subcooling are measured relative to it.
- Compression ratio
- Absolute discharge pressure divided by absolute suction pressure; high ratios raise discharge temperature and reduce compressor capacity.
- TXV function
- A thermostatic expansion valve modulates refrigerant flow to maintain a nearly constant evaporator superheat as load and pressure change.
- Recovery cylinder limit
- A refrigerant recovery cylinder must not be filled above 80 percent of its capacity to allow for liquid expansion and prevent hydrostatic rupture.
- Deep vacuum level
- A vacuum of about 500 microns is commonly used for dehydration; it removes moisture and noncondensables before charging.
- Ohm’s law
- The relationship E equals I times R; voltage equals current times resistance, and power equals voltage times current in a resistive circuit.
- R terminal
- The 24-volt hot terminal on a low-voltage thermostat; it supplies control power to cooling, heating, and fan circuits.
- Run capacitor
- A microfarad-rated capacitor that stays in the motor circuit to improve running torque and power factor; failure causes high current and poor performance.
- Contactor
- An electromechanical switch that uses a low-voltage coil to close line-voltage contacts, starting compressors, fans, or electric heaters.
- Locked rotor amps
- The current a motor draws at startup when the rotor is stationary; used with nameplate data for branch-circuit and overload sizing.
- Disconnect within sight
- An electrical disconnecting means installed within sight of and within 50 feet of equipment, capable of being locked in the open position.
- Manual J
- ACCA’s residential load calculation method that estimates room-by-room heating and cooling loads from envelope, orientation, infiltration, and internal gains.
- Manual D
- ACCA’s duct design method; it uses room airflow, equivalent length, and friction rate to size ducts and select fittings.
- Friction rate
- The pressure loss per 100 feet of equivalent duct length; residential duct designs commonly use about 0.1 inch water column per 100 feet.
- Equivalent length
- The total duct length plus the pressure-loss equivalent of fittings; elbows and transitions add substantial resistance to airflow.
- Duct area formula
- Cross-sectional duct area in square feet equals airflow in cfm divided by duct velocity in feet per minute.
- Texas Occupations Code 1302
- The Texas statute governing air conditioning and refrigeration contracting, including licensing, technician registration, enforcement, and penalties administered by TDLR.
- 16 TAC Chapter 75
- The Texas Administrative Code chapter containing TDLR rules for air conditioning and refrigeration contractors, technicians, licensing, and enforcement.
- EPA Section 608
- Federal rule requiring certification for technicians who service, repair, or dispose of appliances containing ozone-depleting or substitute refrigerants.
- Fall protection threshold
- OSHA generally requires fall protection for construction work at heights of 6 feet or more above a lower level.
- Lockout tagout
- An energy-control procedure that isolates electrical, gas, or mechanical energy before service and verifies the equipment cannot restart unexpectedly.