CFESA Diagnostic Troubleshooting 2 — Questions and Answers
Question 1: A commercial steamer fails to build pressure. After checking the door gasket seal, the technician should inspect:
- The condensate return line
- The water supply valve, water level probe, and heating elements (Correct answer)
- The safety relief valve only
- The steam trap
Correct answer: The water supply valve, water level probe, and heating elements
A steamer that won't build pressure likely has insufficient water (supply valve, level probe malfunction) or insufficient heat input (failed elements) — all must be checked.
Question 2: On a commercial walk-in cooler, a technician finds the evaporator fan running but the evaporator coil is completely encased in ice. The defrost system should be checked for:
- Low refrigerant charge
- Failed defrost heaters, defrost timer/control, or defrost termination thermostat (Correct answer)
- Dirty condenser coils
- Refrigerant overcharge
Correct answer: Failed defrost heaters, defrost timer/control, or defrost termination thermostat
A completely iced-over evaporator indicates the defrost cycle is not functioning; failed heaters, a stuck defrost timer, or a faulty termination thermostat are the likely causes.
Question 3: A commercial convection oven heats unevenly — hot on one side and cool on the other. After confirming the fan operates, the technician should check:
- The door gasket on the cool side only
- Individual heating elements or burner sections for open circuits or uneven output (Correct answer)
- The thermostat probe location
- Gas supply pressure only
Correct answer: Individual heating elements or burner sections for open circuits or uneven output
Uneven heating in a convection oven is often caused by a failed heating element or burner on one side; checking individual elements for open circuits isolates the faulty component.
Question 4: A commercial deep fryer's oil is overheating well above the setpoint. After confirming the thermostat is calibrated, the technician should test:
- The gas valve for proper closure when the thermostat is satisfied (Correct answer)
- The fryer basket for warping
- The oil filtration pump
- The flue baffle position
Correct answer: The gas valve for proper closure when the thermostat is satisfied
If the thermostat is calibrated and the oil still overheats, the gas valve may be sticking open rather than closing when the thermostat is satisfied, causing continuous heating.
Question 5: A commercial refrigerator's compressor hums but will not start. The most likely cause on a single-phase unit is:
- Open overload protector
- Failed start capacitor or start relay (Correct answer)
- Low refrigerant charge
- High head pressure
Correct answer: Failed start capacitor or start relay
A humming but non-starting compressor on a single-phase unit typically indicates a failed start capacitor or start relay that is not providing the starting torque needed.
Question 6: What diagnostic information does a pressure-temperature (P-T) chart provide to a refrigeration technician?
- Compressor motor amp draw at various pressures
- The saturation temperature of a refrigerant at a given pressure (Correct answer)
- Head pressure limits for specific ambient temperatures
- Refrigerant oil viscosity requirements
Correct answer: The saturation temperature of a refrigerant at a given pressure
A P-T chart correlates refrigerant pressure to its saturation (boiling/condensing) temperature, allowing technicians to determine evaporating and condensing temperatures from gauge readings.
CFESA Diagnostic Troubleshooting 2
A commercial steamer fails to build pressure.
After checking the door gasket seal, the technician should inspect: