Advanced Cooling Concepts
What happens to refrigerant pressure when the condenser coil is dirty?
It rises, because heat cannot transfer to the outdoor air properly.
What safety device detects flames in a gas furnace?
Flame Sensor.
24 volts.
What is the main purpose of return air ducts?
To bring air back to the HVAC unit for reconditioning.
A unit is not cooling, what is the first thing you should check?
Thermostat setting and power supply. (KISS method = Keep it simple stupid.)
What is the main purpose of the TXV (Thermostatic Expansion Valve)
It regulates the flow of refrigerant into the evaporator based on superheat.
What does the limit switch protect against?
Overheating.
What is Ohm's Law?
Voltage= current x Resistance (V=I x R).
What is a common issue caused by undersized duct?
High Static Pressure and noisy airflow.
Frost on the evaporator coil can indicate what?
Low airflow or Low refrigerant charge.
What phase is the refrigerant in at the compressor inlet?
Low-pressure Vapor.
What's the purpose of the inducer draft motor?
It clears the exhaust fumes from the heat exchanger before ignition.
What is a common symptom of a failing capacitor
Motor starts slowly, hums, or won't start at all.
What is the benefit of balancing dampers in a duct system?
They help even out airflow to different rooms.
What is a likely cause of low suction pressure and normal head pressure?
Restricted metering device or Airflow issue.
What is one effect of low airflow across the evaporator coil?
Reduced cooling capacity and possible coil freezing.
What is one cause of short cycling in a furnace?
Oversized unit, dirty filter, or faulty thermostat placement.
What is the difference between a relay and a contactor?
A relay controls low-current circuits; A contactor switches higher loads (like compressors).
What is the recommended maximum air velocity in residential ducts?
A blower runs constantly even when the system is off. What could cause it?
Stuck relay, fan switch set to "ON", or a faulty control board.
A system has high superheat and low subcooling. What is the likely problem?
Undercharged system. (Low Refrigerant.)
What is "secondary heat exchange" in a high-efficiency furnace?
What does an open winding in a motor indicate?
The motor is electrically broken (no continuity) and needs replacement.
What is the difference between static pressure and velocity pressure?
Static = potential energy (pressure on duct walls);
Velocity = moving air energy.
How can a technician determine if a compressor is grounded?
Use a multimeter - continuity between windings and casing means it is grounded (Bad).