Refrigerators and freezers
A fridge that runs but will not cool usually starts with the condenser coils. In city apartments those coils sit under the unit or behind a kick plate, packed with pet hair and dust that make the compressor work twice as hard. Next the tech listens for the evaporator fan behind the freezer panel, because a dead fan leaves a freezer cold and the fresh food side warm. If frost has built up on the evaporator coil, the defrost system is next: heater, defrost thermostat and control board, each checked for continuity with a multimeter. Repeated clicking with no compressor hum often means the start relay or overload has failed.
Washers
A washer full of standing water almost always comes down to the drain path. The tech clears the pump filter of coins, socks and hair ties, then tests the drain pump motor directly. A machine that refuses to start or spin often has a failed lid switch on a top-loader or a bad door lock assembly on a front-loader. Loud banging during spin points to the suspension: worn shock absorbers, springs or a cracked spider arm on the drum.
Dryers
No heat in an electric dryer usually means a blown thermal fuse or a burned-out heating element, and no heat in a gas dryer often means a weak igniter or failed gas valve coils. A drum that sits still suggests a broken belt, while squealing or thumping points to worn drum rollers or the idler pulley. What people tend to miss is that a thermal fuse fails for a reason, and the reason is usually a blocked vent. In high-rise buildings with long vent runs, a good tech checks airflow at the exhaust before closing out the job.
Dishwashers
Water sitting in the bottom of the tub starts with the filter and drain hose, then the drain pump. If the unit hums but never fills, the water inlet valve and its solenoid get tested. Dishes that come out cold and wet usually mean a failed heating element or high-limit thermostat.
Ranges, ovens and cooktops
When a gas oven clicks without lighting, the hot surface igniter has usually weakened and no longer draws enough current to open the safety valve. The tech checks that with a clamp meter, and may use a manometer to confirm gas pressure at the regulator. Electric ovens that heat unevenly often have a broken bake or broil element, and ovens that run hot or cold usually have a drifting temperature sensor, checked against the resistance chart on the tech sheet.
Microwaves
If the light and turntable work but food stays cold, the magnetron, high-voltage diode or capacitor may be at fault. A microwave that is completely dead often has a blown fuse caused by a failed door switch. Never open a microwave yourself: the high-voltage capacitor can hold a lethal charge long after the unit is unplugged, and a trained tech discharges it safely before touching anything.