Refrigerators and freezers
When a refrigerator runs without cooling, the condenser coils are usually the first stop. In apartments, those coils hide underneath or behind the toe grille, matted with dust and pet hair that force the compressor to overwork. 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. 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. What people tend to miss is that a thermal fuse fails for a reason, and the reason is usually a blocked 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 water inlet valve and its solenoid get tested. Dishes coming out wet and cold suggest a failed heating element or high-limit thermostat.
Ranges, ovens and cooktops
A gas oven that clicks but will not light usually has a weak hot surface igniter that no longer pulls 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 totally dead microwave often has a blown internal fuse triggered by a bad 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.