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Hp practice questions

23 questions from the hvac service and troubleshooting practice test.

Hp practice test

10 questions, graded as you go, with the reason for every answer. No sign-up.

What this covers

Sample questions

A heat pump whose reversing valve is energized in cooling (O terminal) heats the house when the thermostat calls for cooling. There is 24 V between O and C at the outdoor unit, and the solenoid coil measures open (OL). What is the fault?

  1. A thermostat set for a B-type valve
  2. An open reversing valve solenoid coil
  3. A reversing valve slide stuck in mid-position
  4. A defrost board stuck in defrost
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B. An open reversing valve solenoid coil

The control signal is arriving, but an open coil cannot create the magnetic field that shifts the pilot valve, so the valve stays in its de-energized position, which is heating. A thermostat set to B would not put 24 V on the O wire during a cooling call.

Reference: Heat pump reversing valve; solenoid coil testing

A heat pump stays in heating when cooling is called. The solenoid coil has 24 V across it, measures normal resistance and holds a screwdriver tip magnetically. What is the most likely fault?

  1. The thermostat is not energizing the O terminal at all
  2. The solenoid coil has an open winding
  3. The valve's slide or pilot is stuck mechanically
  4. The defrost thermostat is stuck open
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C. The valve's slide or pilot is stuck mechanically

Voltage, resistance and a magnetic pull prove the electrical side is working. If the valve still does not shift, the pilot passages or main slide are stuck, often after contamination or with too little pressure difference to move the slide.

Reference: Heat pump reversing valve diagnosis

A heat pump defrosts normally, but ice builds up across the bottom rows of the outdoor coil and in the base pan through the winter. What is the most likely cause?

  1. The system is overcharged with refrigerant
  2. Meltwater cannot drain away and refreezes
  3. The defrost thermostat is stuck closed
  4. The outdoor fan is running too fast
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B. Meltwater cannot drain away and refreezes

Defrost water has to leave through the base pan drain openings. If they are blocked, or the unit sits in snow or flat on a slab, the water refreezes and the ice grows upward from the bottom. Raising the unit and clearing the drain paths is the fix.

Reference: Heat pump installation; defrost drainage and clearances

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