To repair a room air conditioner, diagnose the problem and likely cause, whether it's not running or just not cooling. If the air conditioner is not running, replace the electrical switch. If it isn't cooling, replace the thermometer.
The first step of repairing a room air conditioner is determining the problem. Common problems include the unit not running or inadequate cooling. If the unit doesn't run, wait 30 minutes and then press the reset button. If that doesn't work, look for burns around the terminal, which is a sign of a faulty switch.
To replace a faulty switch, unplug the unit and remove the control panel. This exposes the switch. Unscrew the switch from its frame, disconnecting the wires. Purchase a new switch and reconnect the wires before screwing it into place. Replace the control panel.
Inadequate cooling is usually due to a thermostat issue. Remove the control panel and the grill. Tag the location of the sensor bulb before removing the thermostat. Use a volt-ohm-millimeter tool to test the efficacy of the thermostat. A zero reading indicates a functioning thermostat, while anything else indicates malfunction. If the thermostat is malfunctioning, purchase a new one and install it exactly how the old one was. Make sure the sensor bulb is in the exact same location as the old one.