The thermostat in your window air conditioner is hiding behind the control panel. It is not just a dial; it is a mechanical sensor system that controls the compressor. If your unit blows warm air while the fan runs, or if it cycles on and off too quickly, the problem might be a faulty thermostat or a clogged drain.
Here is the step-by-step process to test and replace the thermostat, plus how to clear out the drain ports that cause leaks.
Testing the Thermostat Sensing Bulb
You need to get inside the unit to reach the thermostat. Start by removing the grille and the control panel.
Be careful. The thermostat has a special sensing bulb attached to it. This thin tube extends from the thermostat housing deep into the evaporator coil area. Its job is to sense the temperature of the air passing over the coils. When that temperature drops, the thermostat tells the compressor to shut off.
Before you pull anything out, tag the location of the bulb. You must return it to the exact same spot on the coil when you put it back. If you move it, the temperature reading will be wrong, and the unit will not cool properly.
How to Check the Electrical Connection
Once the thermostat is out, you can test it with a Volt-ohmmeter (VOM) or a multimeter. Set the meter to the RX1 scale.
Clip the probes to the thermostat terminals. Turn the temperature control dial to the coldest setting. Look at the meter.
If the meter reads zero ohms, the thermostat is functioning properly. The circuit is closed.
If the reading is higher than zero, the contacts are bad. You need to replace the thermostat. Buy a replacement of the exact same type. If the old unit was held to the frame with screws, clips, or metal tabs, connect the new one using the same method.
Warning: If the thermostat has more than two lead wires connected to it (excluding the sensing bulb wire), do not attempt to test or replace it. Call a professional service person. Complex wiring requires expert handling.
Clearing Clogged Drain Ports
While you have the panel off, check the drainage system. As the air conditioner runs, condensed moisture and water vapor from the evaporator coil are funneled through drain ports. These are openings between the partition in the middle of the evaporator coil and the condenser coil.
The fan blows this moisture against the condenser coil, where it dissipates into the air. But if these ports get clogged with dirt, the water has nowhere to go.
The result is water leaking from the appliance, usually through the bottom of the grille.
To prevent this, clean the ports at the beginning of every cooling season and every month during the season. Use a short piece of wire hanger or the blade of a pocketknife to dislodge dirt. Check the condenser side of the air conditioner too. Some models have a drain port along the bottom edge of the cabinet frame. Clean that out when you clean the other ports.
Tools You Will Need
You do not need a full toolbox for this job. Just have these items on hand:
- Screwdriver
- Volt-ohmmeter or multimeter
- Replacement thermostat
- Wire hanger or pocketknife for cleaning
Routine maintenance of the fan, motor, and compressor keeps your unit running efficiently. Fixing the thermostat and drain is a quick way to extend the life of the unit and stop water damage. If the wiring looks complex, stop. Call a pro.
