Diagnostic Troubleshooting Flashcards

A commercial griddle's thermostat bulb has lost its charge. How does this typically affect the thermostat's behavior?

Answer: The thermostat locks in the closed position, causing continuous heating up to the high limit

A thermostat with a lost bulb charge has no sensing pressure to open the contacts, so it defaults to the closed (call for heat) position, causing uncontrolled heating.

When diagnosing a commercial dishwasher that fails to sanitize, what reading should a technician verify using a service thermometer?

Answer: Final rinse water temperature at the rack surface (minimum 180°F for high-temp units)

Sanitization is verified by confirming final rinse temperature at the rack surface meets the minimum 180°F requirement, as this is where sanitization actually occurs.

A technician measures 0 volts at a commercial oven's heating element terminals while the thermostat is calling for heat. The next diagnostic step is:

Answer: Trace back through the control circuit to find the open in the circuit (thermostat contacts, safety limit, relay)

Zero voltage at the element with a call for heat means the control circuit is open; the technician must trace back through the wiring diagram to find the open contact or blown fuse.

What does a megohmmeter (megger) test on a compressor motor winding reveal?

Answer: Insulation resistance to detect winding-to-ground faults

A megohmmeter applies high voltage to test insulation resistance between motor windings and ground, detecting insulation breakdown that can cause ground faults or motor failure.

A commercial refrigerator has a moisture indicator (sight glass) showing a yellow color. This indicates:

Answer: Moisture is present in the refrigerant system

A yellow or discolored moisture indicator (sight glass) signals that moisture has entered the refrigerant system and the filter drier should be replaced.

When a commercial gas range burner will not light via electronic ignition but the pilot-less igniter sparks normally, the technician should next check:

Answer: The igniter electrode gap and gas valve operation

If the igniter sparks but the burner does not light, either the electrode is mispositioned relative to the burner or the gas valve is not opening to supply gas to the burner.