Compressor & Sealed System
This component pumps refrigerant through the sealed system and is the heart of the refrigeration cycle.
The compressor
This component tells the compressor and fans when to cycle on and off based on cabinet temperature.
The thermistor (or temperature control board)
This electric heating element melts accumulated frost off the evaporator coil during the defrost cycle.
The defrost heater
This fan circulates air over the condenser coil to dissipate heat, and is typically found at the bottom rear of the refrigerator.
The condenser fan motor
This is the document a technician must locate before diagnosing any unfamiliar refrigerator — it contains wiring diagrams, fault codes, and component locations.
The service manual (or tech sheet, found behind the kickplate or taped inside the unit)
This component removes heat from the refrigerant, causing it to condense from a gas to a liquid. Usually located on the back or bottom of the unit.
The condenser coil
This safety device will shut the compressor off if the discharge temperature or pressure becomes dangerously high.
The overload protector (or thermal overload)
This component ends the defrost cycle when the evaporator reaches a set temperature, preventing overheating.
The defrost thermostat (or defrost limiter)
A refrigerator where the freezer is cold but the fresh food section is warm likely has a problem with this component.
The damper (air diffuser) or the evaporator fan motor not circulating air to the fresh food section
A technician uses this tool to measure the actual operating pressures of the sealed system at the low and high side.
Gauge Set
This small device meters refrigerant flow into the evaporator and controls the pressure drop in the system.
Metering device/Capillary Tube, Drier Filter
This relay is responsible for starting the compressor by briefly engaging the start winding, then dropping out once the motor is running.
The start relay
This component initiates the defrost cycle on a schedule, typically every 8 to 12 hours of compressor run time.
The defrost timer (or adaptive defrost control board)
This component seals the cabinet door and is the first thing to inspect when a refrigerator is running constantly but not maintaining temperature.
The door gasket
When a compressor hums but doesn't start and the start relay rattles, a technician should perform this quick field test on the relay.
The shake test — a relay that rattles when shaken has a broken internal component and should be replaced
This is the process where refrigerant absorbs heat inside the cabinet and changes from liquid to gas, causing cooling.
Evaporation (the refrigerant boiling off inside the evaporator coil)
On a refrigerator with an inverter compressor, this component converts AC power to variable DC frequency to control compressor speed.
The inverter board (or variable frequency drive)
Excessive frost buildup on the back wall of a freezer that the customer reports regularly is a classic symptom of this defrost system failure.
A failed defrost heater, defrost thermostat, or defrost timer — the defrost cycle is not completing
This refrigeration system value rises when condenser coils are dirty or airflow is restricted, forcing the compressor to work harder and lowering efficiency.
Discharge pressure (head pressure)
A technician measures 120 VAC to a refrigerator defrost heater during forced defrost, but the heater never warms up. The heater reads OL on the meter. Identify the failed component.
What is an open defrost heater?
A refrigerator compressor that runs constantly but the freezer isn't getting cold likely has this sealed system failure.
Low refrigerant charge / refrigerant leak
Before replacing a compressor, a technician should always perform this test to verify the motor windings are not grounded or open.
Resistance test of the compressor windings (S, C, R pins with a multimeter)
After a defrost cycle, this component removes heat and moisture from inside the cabinet by circulating air across the evaporator.
The evaporator fan motor
A refrigerator’s freezer temperature is normal, but product near the top shelves softens during heavy usage. The evaporator fan motor tests good, frost pattern is normal, and the condenser is clean. What is the issue?
What is blocked air vents
Before writing up a service invoice, a technician must look up the repair labor time in this resource to ensure accurate billing.
The Blue Book (labor guide)