the water tank full light came on but the tank is actually empty, how do i fix this sensor?

Diagnosis

The "Water Tank Full" indicator on the Whynter ARC-122DS is triggered by a mechanical float switch located in the internal condensate tray at the bottom of the unit. This float is a small, lightweight plastic cylinder that rises as water accumulates. When it reaches a specific height, it pushes a micro-switch or completes a magnetic circuit, signaling the control board to shut down the compressor to prevent an overflow that would leak onto your flooring. The issue occurs when the float becomes physically jammed or "stuck" in the upward position, even after the tank has been drained. This is typically caused by the buildup of "slime"—a combination of dust, airborne pollutants, and biological growth—or mineral scale from hard water. In some cases, the float can become wedged against the side of the plastic reservoir due to a slight shift in the unit's leveling, or the sensor itself has developed a mechanical failure where the spring mechanism no longer pulls the float back down.

How to Fix It

To reset the sensor and clear the error light, follow these precise steps to manually dislodge the float and clean the reservoir:

1. Power down the unit completely and unplug the power cord from the wall outlet to prevent electrical shorts during the cleaning process.
2. Locate the drain plug at the rear bottom of the unit. Place a shallow pan underneath and remove the rubber stopper to ensure every last drop of residual water is evacuated.
3. Gently tilt the entire unit backward at a 15-degree angle. While holding it tilted, shake the unit side-to-side with moderate force. This movement is designed to break the surface tension of any slime or mineral deposits holding the float in the "up" position.
4. If the light remains on, use a can of compressed air. Locate the small gap around the drain plug or the ventilation slats at the bottom. Blow short bursts of air into the base of the unit to physically push the float back down to the bottom of the tray.
5. Allow the unit to sit level for 5 minutes. Plug the unit back in and power it on. The "Water Tank Full" light should now be extinguished, and the compressor should engage.

If That Didn't Work

• Deep Chemical Clean: Mix a solution of one part white distilled vinegar to four parts warm water. Carefully pour about one cup of this solution into the base of the unit through the drain port. Let it sit for 30 minutes to dissolve calcium deposits and break down the biofilm jamming the float. Flush it out thoroughly with clean water.
• Manual Float Manipulation: If the float is permanently stuck, you may need to access the internal tray. Remove the outer plastic casing by unscrewing the perimeter screws. Locate the condensate tray at the bottom and manually pull the float down using a pair of needle-nose pliers. Check for any debris or foreign objects (like small pieces of insulation) that may have fallen into the tray.
• Sensor Bypass/Replacement: If the float is physically cracked or the micro-switch is faulty, the sensor needs replacement. Check the continuity of the switch using a multimeter. If the circuit remains "closed" even when the float is down, the switch has failed and must be replaced with a compatible 2-pin micro-switch.
• Leveling Adjustment: Ensure the unit is on a perfectly flat surface. If the unit leans forward or to one side, the float can rub against the wall of the reservoir, creating friction that prevents it from dropping. Use a bubble level and adjust the placement of the unit.

Heads Up

• Continuous Drainage: To avoid this issue entirely, connect a standard 5/8" internal diameter garden hose to the continuous drain port. This bypasses the internal tank and prevents the float from ever rising.
• Filter Maintenance: Dirty air filters allow more dust into the unit, which mixes with condensate to create the "slime" that jams the float. Clean your filters every two weeks.
• Avoid Harsh Chemicals: Never use bleach or caustic drain cleaners inside the condensate tray, as these can corrode the aluminum cooling fins or degrade the plastic reservoir.
• Storage Tip: Before storing the unit for the winter, ensure you drain the bottom tank completely and run the unit on "Fan Only" mode for 2 hours to dry out the internal tray.