✓ TradeExamPro

TradeExamPro › HVAC & Refrigeration › HVAC service and troubleshooting

Ctrl practice questions

13 questions from the hvac service and troubleshooting practice test.

Ctrl practice test

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

What this covers

Sample questions

The outdoor unit will not start from the thermostat. When the technician jumpers R to Y at the thermostat subbase, the outdoor unit starts and runs normally. What is at fault?

  1. The contactor
  2. The thermostat cable
  3. The thermostat
  4. The transformer
Show the answer

C. The thermostat

A jumper at the subbase does exactly what the thermostat's cooling contact should do, using the same wires. Since the unit runs, the cable, transformer and contactor are all proven good and the thermostat is not closing R to Y.

Reference: Thermostat troubleshooting; jumper test

The blower will not run when the thermostat's fan switch is set to On. Jumpering R to G at the air handler's terminal strip starts the blower. Where is the fault?

  1. In the blower motor or its run capacitor
  2. In the thermostat or the G conductor of the cable
  3. In the air handler's blower relay or board
  4. In the control transformer's secondary winding
Show the answer

B. In the thermostat or the G conductor of the cable

The jumper proves that everything from the G terminal onward, including the relay and motor, works when it receives 24 V. The signal is therefore not arriving, so the thermostat's fan contact or the G wire between thermostat and air handler is open.

Reference: Thermostat troubleshooting; fan circuit

A new electronic thermostat on a gas furnace cycles the burners on and off every two or three minutes with a call for heat still present at the display. The furnace runs normally when R and W are jumpered. What should be checked?

  1. The furnace's high-limit switch for a low trip temperature
  2. The thermostat's heating cycle-rate setting for the equipment type
  3. The furnace's flame sensor for a weak microamp signal
  4. The gas valve's manifold pressure adjustment screw
Show the answer

B. The thermostat's heating cycle-rate setting for the equipment type

Electronic thermostats control cycles per hour through an installer setting matched to the equipment type; a setting meant for fast-cycling equipment makes a gas furnace run in very short bursts. The jumper test shows the furnace itself holds a steady call without trouble.

Reference: Thermostat configuration; cycle rate

Other topics