Denso Air Conditioner Error Code PU

The PU error code on a Denso air conditioner indicates that the condensation overflow protection system has been triggered. Specifically, the drain pan float switch has remained in the OFF position continuously for 60 seconds, signaling that water has accumulated to a level that exceeds safe operating limits within the internal drain pan. The unit's internal drain pump is responsible for actively evacuating condensate, and when the float switch detects sustained high water levels rather than a momentary fluctuation, the system shuts down to prevent water damage to the unit and surrounding structure.

The internal drain pump operates by drawing condensate from the collection pan and pushing it through the drain hose to an appropriate discharge point. When a blockage, excessive kink, or restriction exists in the drain hose, water cannot exit efficiently and backs up into the pan. The float switch, a buoyancy-activated sensor, rises with the water level and cuts the circuit once a threshold is reached. If this condition persists for 60 seconds without recovery, the PU fault is logged and the unit halts normal operation.

Common root causes include kinked or crushed drain hose sections, biological buildup such as algae or slime inside the hose or drain pan, a failed internal drain pump motor, or a float switch that is stuck or has become fouled with debris. In some cases, the drain hose discharge point may be submerged or have inadequate gradient, creating backpressure that prevents proper flow. Addressing the drain path is the correct first step before assuming component failure.