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Error code reference

Mitsubishi Air Conditioner Error Code E.P24

24 VDC power fault

Mitsubishi codesMitsubishi air conditioner codes

24 VDC power fault - 24 VDC power output from PC terminal is shorted, power output shut off.

First step from the service manual

Check for a short circuit in the PC terminal output and verify 24V external power supply voltage is correct.

The complete diagnostic procedure includes additional test steps, resistance specifications, wiring diagram references, and component test points.

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What E.P24 means on a Mitsubishi air conditioner

The E.P24 error code on a Mitsubishi air conditioner indicates a 24 VDC power fault originating at the PC terminal output. This terminal supplies 24 volts DC to external control devices or field-wired accessories connected to the unit's control board. When the control circuit detects that the 24V output has been pulled down by an abnormal load condition, specifically a short circuit on the output line, the board's protective circuitry shuts off power to that terminal to prevent component damage. The system will not resume normal operation until the fault condition is cleared.

The PC terminal is part of the unit's low-voltage control interface and is commonly used to power external components such as remote controllers, building automation system interfaces, or field-installed accessories. A short circuit on this line can occur due to wiring faults, failed external components drawing excessive current, or damaged insulation causing conductor contact. The 24V supply voltage level itself may also be out of spec if the internal power supply circuit has degraded, which can trigger the same fault.

Diagnosis begins with a visual and electrical inspection of all wiring connected to the PC terminal. The short circuit must be isolated and corrected before the output protection will reset. Using a multimeter to check resistance across the PC terminal output to ground will reveal a shorted condition. If the wiring checks out clean, the external 24V power supply voltage should be measured directly to confirm it falls within the specified 24 VDC range. A failed control board generating incorrect output voltage is also a possible root cause if no external fault is found.

Source: manufacturer service documentation.

Common causes of E.P24

  1. 01

    Short circuit in PC terminal wiring

    Wiring / connection

    Field-wired cables connected to the PC terminal may have damaged insulation, pinched conductors, or a miswired connection causing a direct short to ground. Inspect all wiring routed to the PC terminal for physical damage or incorrect termination.

  2. 02

    Failed or shorted external accessory

    Part replacement

    An external device powered by the PC terminal output, such as a remote interface or building automation module, may have failed internally and is presenting a short circuit to the 24V supply. Disconnect external devices one at a time to isolate the faulty component.

  3. 03

    Incorrect 24V external power supply voltage

    Part replacement

    If an external 24V power supply feeds into this circuit, its output voltage may be out of range due to component aging or failure, causing the protection circuit to activate. Measure the supply voltage directly with a multimeter to confirm it is within specification.

  4. 04

    Faulty control board 24V output circuit

    Part replacement

    If no wiring or external device fault is found, the internal power supply circuit on the PC board itself may have failed, producing a degraded or shorted 24V output. This would require replacement of the control board.

  5. 05

    Moisture or contamination at the PC terminal

    Wiring / connection

    Condensation or debris on the control board terminal block can create a low-resistance path that mimics a short circuit. Inspect the terminal block area for signs of moisture, corrosion, or foreign material.

See the test procedure for each cause

Frequently asked questions about E.P24

What does E.P24 mean on a Mitsubishi air_conditioner?
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.
How do I fix an E.P24 error on my Mitsubishi air conditioner?
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.
Is it safe to keep running my Mitsubishi air conditioner with an E.P24 error?
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.
Will resetting my Mitsubishi air conditioner clear the E.P24 error?
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.
How much does it cost to repair an E.P24 error on a Mitsubishi air conditioner?
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.

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