Components
What are the four main components of an AC system?
Explain sensible heat
Sensible heat is the thermal energy transferred to or from a substance that results in a change in temperature but no change in phase.
What causes an evaporator coil to freeze?
AC runs but does not cool. What do you check?
What are the steps to pull a vacuum?
What's the difference between a TXV and a fixed metering device?
A TXV adjusts refrigerant flow based on evaporator load. A fixed metering device delivers a constant amount of refrigerant.
Explain latent heat
In HVAC, latent heat is the hidden energy absorbed or released when moisture in the air changes state(like water vapor turning into liquid condensation). Crucially, this happens without any change to the air's actual temperature.
How do you test a capacitor?
Turn off power, discharge capacitor safely, remove wires, set meter to capacitance, compare reading to capacitor rating (usually ±6%).
Common causes of low airflow?
Why verify airflow before charging?
Poor airflow affects pressures and temperatures, leading to incorrect refrigerant charge.
What's the voltage at a residential condenser contractor? Line side/load-side and coil
What is superheat?
the amount of heat added to a refrigerant vapor after it has completely boiled into a gas inside the evaporator coil
Transformer has no 24V output. What do you check?
Compressor does not start. What do you check?
How do you check refrigerant leaks?
Difference between series and parallel circuits?
Series circuits have one path for current. Parallel circuits have multiple paths and maintain voltage across components.
What is subcooling?
Subcooling in HVAC is the process of cooling liquid refrigerant below its condensing (saturation) point. By removing extra heat after the refrigerant turns from gas to liquid, it guarantees only 100% liquid reaches the expansion valve. This prevents bubbles ("flash gas") and maximizes cooling capacity
Causes of a breaker tripping?
A compressor is drawing locked rotor amps but not starting. What could be wrong?
What are signs of a restricted metering device?
What is the difference between a run capacitor and a start capacitor?
A start capacitor provides extra torque during startup; a run capacitor stays in the circuit to improve motor efficiency.
What is static pressure?
Static pressure is resistance to airflow inside ductwork and HVAC equipment. High static pressure reduces efficiency and airflow.
What is the purpose of a capacitor in an HVAC system?
A capacitor helps start and/or run motors by providing phase shift and stored electrical energy.
The blower motor runs but the outdoor unit does not start. What would you check?
What causes a low-pressure switch to trip during cooling operation?
Low refrigerant charge, evaporator airflow problems, restriction in refrigerant flow, or freezing conditions.