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. Heavy frost on the evaporator coil points to the defrost system, so the heater, defrost thermostat and control board each get a continuity check with a multimeter. Repeated clicking with no compressor hum often means the start relay or overload has failed.
Washers
Standing water in a washer usually traces back 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. Heavy banging on spin points to suspension trouble: tired shocks, worn springs or a cracked drum spider.
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 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 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 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
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.
