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. Heavy banging on spin points to suspension trouble: tired shocks, worn springs or a cracked drum spider.
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 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
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 split bake or broil element, and an oven that runs hot or cold usually has a drifting temperature sensor tested against the tech sheet resistance chart.
Microwaves
If the light and turntable work but food stays cold, the magnetron, high-voltage diode or capacitor may be at fault. A totally dead microwave often has a blown internal fuse triggered by a bad door switch. Do not open a microwave on your own, because the high-voltage capacitor can hold a lethal charge long after unplugging, and a trained tech discharges it safely before any work begins.
