NYC THERMOSTAT
REPAIRER (DCAS) –
CERTIFICATION
PRACTICE EXAM
Questions With Correct
Answers (Verified Answers)
Plus Rationales 2026 Q&A |
Instant Download Pdf A+
Grade Guarantee Verified By
Professionals
1. A residential thermostat is not turning on the HVAC system even after battery
replacement. What is the MOST likely cause? ✓
Answer: Loose low-voltage wiring connection
Rationale: A disconnected or loose R and C wire will prevent control signal transmission to
the HVAC system even if the thermostat has power.
2. Which component in a thermostat primarily senses ambient room temperature? ✓
Answer: Thermistor sensor
Rationale: A thermistor changes resistance based on temperature and provides input to the
thermostat control board.
,3. A thermostat display is blank despite confirmed power at the breaker. What should be
checked first? ✓
Answer: Transformer output voltage
Rationale: A failed HVAC transformer will prevent low-voltage power from reaching the
thermostat.
4. In HVAC control systems, what does the “R” wire represent? ✓
Answer: Power supply (24V hot)
Rationale: The R terminal supplies 24V AC power from the transformer to the thermostat.
5. A thermostat is short cycling the furnace. What is a probable cause? ✓
Answer: Improper anticipator or calibration setting
Rationale: Incorrect heat anticipation settings can cause rapid cycling of heating equipment.
6. Which tool is MOST appropriate for verifying thermostat voltage? ✓
Answer: Digital multimeter
Rationale: A multimeter accurately measures low-voltage AC/DC signals in HVAC systems.
7. A cooling system does not activate when thermostat is set to COOL. What wire should be
checked first? ✓
Answer: Y wire
Rationale: The Y terminal controls the compressor contactor for cooling.
8. What is the purpose of the C wire in modern thermostats? ✓
Answer: Provides continuous 24V return path
Rationale: The common wire completes the circuit for continuous thermostat power.
9. A thermostat reads incorrect room temperature. What is the MOST likely issue? ✓
Answer: Sensor calibration failure or obstruction
Rationale: Dust or miscalibration affects thermistor accuracy.
, 10. What safety step must be performed BEFORE servicing a thermostat? ✓
Answer: Disconnect HVAC power at breaker
Rationale: This prevents electrical shock and equipment damage.
11. A heat pump system is not switching between heating and cooling modes. What
component may be faulty? ✓
Answer: Reversing valve control circuit
Rationale: The reversing valve directs refrigerant flow for mode switching.
12. Which thermostat setting prevents frequent system cycling? ✓
Answer: Deadband setting
Rationale: Deadband creates a temperature range to prevent rapid on/off cycling.
13. A thermostat only works intermittently. What is a likely cause? ✓
Answer: Loose terminal screws
Rationale: Intermittent connections disrupt consistent control signals.
14. What voltage is typically used in residential thermostat systems? ✓
Answer: 24 volts AC
Rationale: Low-voltage systems are standard for residential HVAC control.
15. A thermostat fan runs continuously regardless of settings. What wire is MOST likely
shorted? ✓
Answer: G wire
Rationale: The G terminal controls the blower fan relay.
16. What is the purpose of the W terminal? ✓
Answer: Heating control signal
Rationale: The W wire activates the heating system.
REPAIRER (DCAS) –
CERTIFICATION
PRACTICE EXAM
Questions With Correct
Answers (Verified Answers)
Plus Rationales 2026 Q&A |
Instant Download Pdf A+
Grade Guarantee Verified By
Professionals
1. A residential thermostat is not turning on the HVAC system even after battery
replacement. What is the MOST likely cause? ✓
Answer: Loose low-voltage wiring connection
Rationale: A disconnected or loose R and C wire will prevent control signal transmission to
the HVAC system even if the thermostat has power.
2. Which component in a thermostat primarily senses ambient room temperature? ✓
Answer: Thermistor sensor
Rationale: A thermistor changes resistance based on temperature and provides input to the
thermostat control board.
,3. A thermostat display is blank despite confirmed power at the breaker. What should be
checked first? ✓
Answer: Transformer output voltage
Rationale: A failed HVAC transformer will prevent low-voltage power from reaching the
thermostat.
4. In HVAC control systems, what does the “R” wire represent? ✓
Answer: Power supply (24V hot)
Rationale: The R terminal supplies 24V AC power from the transformer to the thermostat.
5. A thermostat is short cycling the furnace. What is a probable cause? ✓
Answer: Improper anticipator or calibration setting
Rationale: Incorrect heat anticipation settings can cause rapid cycling of heating equipment.
6. Which tool is MOST appropriate for verifying thermostat voltage? ✓
Answer: Digital multimeter
Rationale: A multimeter accurately measures low-voltage AC/DC signals in HVAC systems.
7. A cooling system does not activate when thermostat is set to COOL. What wire should be
checked first? ✓
Answer: Y wire
Rationale: The Y terminal controls the compressor contactor for cooling.
8. What is the purpose of the C wire in modern thermostats? ✓
Answer: Provides continuous 24V return path
Rationale: The common wire completes the circuit for continuous thermostat power.
9. A thermostat reads incorrect room temperature. What is the MOST likely issue? ✓
Answer: Sensor calibration failure or obstruction
Rationale: Dust or miscalibration affects thermistor accuracy.
, 10. What safety step must be performed BEFORE servicing a thermostat? ✓
Answer: Disconnect HVAC power at breaker
Rationale: This prevents electrical shock and equipment damage.
11. A heat pump system is not switching between heating and cooling modes. What
component may be faulty? ✓
Answer: Reversing valve control circuit
Rationale: The reversing valve directs refrigerant flow for mode switching.
12. Which thermostat setting prevents frequent system cycling? ✓
Answer: Deadband setting
Rationale: Deadband creates a temperature range to prevent rapid on/off cycling.
13. A thermostat only works intermittently. What is a likely cause? ✓
Answer: Loose terminal screws
Rationale: Intermittent connections disrupt consistent control signals.
14. What voltage is typically used in residential thermostat systems? ✓
Answer: 24 volts AC
Rationale: Low-voltage systems are standard for residential HVAC control.
15. A thermostat fan runs continuously regardless of settings. What wire is MOST likely
shorted? ✓
Answer: G wire
Rationale: The G terminal controls the blower fan relay.
16. What is the purpose of the W terminal? ✓
Answer: Heating control signal
Rationale: The W wire activates the heating system.
