Refrigerators and freezers
When a refrigerator runs without cooling, the condenser coils are usually the first stop. 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. Then the tech listens for the evaporator fan behind the freezer wall, since a failed fan keeps the freezer cold while the fridge side warms up. 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. A clicking sound every few minutes with no hum often means a failed start relay or overload on the compressor.
Washers
A washer full of standing water almost always comes down to the drain path. The tech checks the pump filter for socks, coins and hair ties, then tests the drain pump motor itself. If the machine will not start or spin, the lid switch on a top-loader or the door lock assembly on a front-loader is a common culprit. Loud banging during spin points to the suspension: worn shock absorbers, springs or a cracked spider arm on the drum.
Dryers
An electric dryer with no heat usually has a blown thermal fuse or dead heating element, while a gas dryer with no heat often has a weak igniter or bad valve coils. A drum that will not turn points to a snapped belt, and a squeal or thump points to worn rollers or an idler pulley. Here is the part people skip: a thermal fuse blows for a reason, and that reason is usually a clogged vent. In high-rises with long shared vent runs, the tech will check airflow at the exhaust before calling the job done.
Dishwashers
Water pooling in the tub starts with a check of the filter and drain hose, then the drain pump. If the unit hums but never fills, the tech tests the water inlet valve and its solenoid. 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 confirms that with a clamp meter and may check gas pressure at the regulator with a manometer. 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
When the light and turntable work but the food stays cold, the magnetron, high-voltage diode or capacitor is a likely suspect. 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.
