Daikin Air Conditioner Error Code P4

P4 indicates a radiation fin thermistor abnormality, meaning the inverter PCB has detected an open or short circuit in the thermistor that monitors heat sink fin temperature. This fault is detected specifically while the compressor is stopped. The system will not operate normally until the fault is diagnosed and resolved.

No. The radiation fin thermistor is a protective sensor for the inverter electronics. Without accurate temperature feedback, the inverter has no way to detect an overheating condition, which could lead to permanent damage to the inverter PCB. The system typically prevents operation when this fault is active, and that protection should not be bypassed.

A power reset may temporarily clear the fault display, but the P4 code will return if the underlying hardware problem with the thermistor or its wiring has not been corrected. Because the fault is detected during compressor stop cycles, the error will reappear quickly once the system attempts normal operation. A reset alone is not a fix and should not substitute for proper diagnosis.

Some diagnostic steps, such as checking connector X111A for corrosion or a loose connection, are within reach of a knowledgeable DIYer. However, measuring thermistor resistance accurately requires a multimeter and some familiarity with reading resistance values. If the inverter PCB needs replacement, that work should be performed by a qualified HVAC technician, as the inverter board carries dangerous voltage levels even when the unit appears powered down.

Repair costs depend heavily on which component has failed. Thermistor replacement is generally the least expensive outcome, typically ranging from around $50 to $150 for the part plus labor. If the inverter PCB itself requires replacement, costs can range from $300 to $800 or more depending on the specific model and regional labor rates.