Mitsubishi Air Conditioner Error Code E.P24

E.P24 indicates a 24 VDC power fault at the PC terminal on the control board. The unit has detected a short circuit on the 24V output line and has shut off power to that terminal as a protective measure. The system will not operate normally until the short is identified and corrected, and the fault condition is cleared.

The unit has automatically shut off the affected 24V output circuit to protect itself, so continued operation poses a risk of further component damage if the underlying short circuit is not addressed. It is advisable to stop using the unit and have a qualified technician inspect and repair the fault before resuming normal operation.

Repair costs depend on the root cause. If the issue is a wiring fault or a damaged external accessory, labor and parts costs could range from around $75 to $300. If the control board requires replacement, costs can increase significantly, typically ranging from $300 to $700 or more depending on the model and local labor rates. A diagnostic visit from a qualified HVAC technician is the first step to getting an accurate estimate.

Start by inspecting all wiring and external devices connected to the PC terminal for short circuits or damage. Disconnect any field-wired accessories and check resistance across the PC terminal output to ground with a multimeter. If the wiring is clear, verify that the 24V external power supply voltage is within the correct range. If no external cause is found, the control board itself may need professional evaluation or replacement.

A simple power reset will typically not permanently clear E.P24 because the fault is caused by a physical short circuit condition that remains present. Even if the unit restarts briefly after a reset, the protection circuit will detect the short again and shut off the output. The underlying wiring or component fault must be corrected first before the error will clear and stay cleared.