Something study on HVAC fild

 

🔹 HVAC Interview Mock Drill (Q & A)

1. Basic Knowledge

Q1: What is HVAC?

👉 HVAC means Heating, Ventilation and Air Conditioning. It controls temperature, humidity and air quality in a building.

Q2: Difference between Split AC, Package Unit, and Chiller?

👉 Split AC: Small capacity, used for single rooms.

👉 Package Unit: Medium capacity, rooftop type, for halls/shops.

👉 Chiller: Large capacity, central system, used in big buildings.

Q3: Function of Compressor, Condenser, Evaporator, Expansion valve?

👉 Compressor: Compresses refrigerant and increases pressure.

👉 Condenser: Rejects heat to outside.

👉 Expansion Valve: Reduces refrigerant pressure.

👉 Evaporator: Absorbs heat and makes cooling.

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2. Refrigerants & Pressure

Q4: Name some common refrigerants and their safety groups.

👉 R-22 (HCFC), R-410A (HFC), R-134a (HFC).

👉 R-22 = Group A1 (low toxicity, low flammability).

👉 R-410A = Group A1.

Q5: Normal suction and discharge pressure of R-22 and R-410A?

👉 R-22: Suction 60–70 psi, Discharge 220–250 psi.

👉 R-410A: Suction 120–140 psi, Discharge 350–400 psi.

Q6: What is superheat and subcooling?

👉 Superheat = Temperature of vapor above saturation (prevents liquid entering compressor).

👉 Subcooling = Temperature of liquid refrigerant below saturation (ensures only liquid enters expansion valve).

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3. Troubleshooting

Q7: If AC is cooling less, what could be the reasons?

👉 Dirty filter, less refrigerant, dirty condenser coil, weak compressor, improper airflow.

Q8: What causes high head pressure?

👉 Dirty condenser, overcharging refrigerant, non-condensables, fan motor problem.

Q9: Why does compressor sweating occur?

👉 Low suction pressure, overfeeding refrigerant, poor insulation, ambient humidity.

Q10: Causes of ice forming on evaporator coil?

👉 Low refrigerant, dirty filter, blower fan problem, low airflow.

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4. Electrical & Controls

Q11: Function of Contactor, Overload, Capacitor?

👉 Contactor = Switch for compressor/fan.

👉 Overload = Protects motor from high current.

👉 Capacitor = Helps motor start and run smoothly.

Q12: What is a thermostat and how does it work?

👉 A thermostat senses temperature and controls compressor ON/OFF automatically.

Q13: Difference between series and parallel connection?

👉 Series: Current same, voltage divided.

👉 Parallel: Voltage same, current divided.

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5. Maintenance

Q14: Steps of preventive maintenance for split AC?

👉 Clean filters, clean condenser & evaporator coil, check refrigerant, check electrical connections, check drainage, test system operation.

Q15: How do you clean condenser and evaporator coils?

👉 Use blower, brush or coil cleaner chemical, wash with water if required.

Q16: How to check and charge refrigerant properly?

👉 Use manifold gauge, check superheat/subcooling, charge refrigerant slowly in vapor or liquid form depending on type.

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6. Safety

Q17: What PPE is required for HVAC technicians?

👉 Safety shoes, gloves, goggles, helmet, mask.

Q18: What safety precautions during refrigerant charging?

👉 Use proper gauge, avoid overcharge, no open flame, proper ventilation, wear PPE.

Q19: Why is nitrogen used during brazing?

👉 To prevent oxidation, scaling, and moisture inside copper pipes.

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7. Advanced / Interview Focused

Q20: What is CFM in HVAC and how is it calculated?

👉 CFM = Cubic Feet per Minute, airflow measurement.

👉 Formula: CFM = (Air Velocity × Area).

Q21: What is psychrometric chart and why important?

👉 It shows relation of dry bulb temp, wet bulb temp, humidity.

👉 Important for designing and balancing air conditioning.

Q22: Difference between VRF/VRV and split AC?

👉 VRF/VRV: Variable refrigerant flow, multiple indoor units with one outdoor, energy efficient, large buildings.

👉 Split AC: One indoor, one outdoor, small capacity.

Q23: What is COP (Coefficient of Performance)?

👉 COP = Cooling or Heating Effect ÷ Power Input.

👉 Higher COP = More efficient system.

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