Abnormal Heat Sink Temperature

Home Appliance Error Codes Mitsubishi Electric Ducted (concealed) AC

Can you still use it? With care until repaired

Who can fix it? Needs a technician

Typical repair time 1 hour – 3 hours

Typical cost SAR 150 to 2,500

What it means

This code appears on the wired remote of Mitsubishi Electric Mr. Slim ducted, ceiling and cassette units. It means the heat sink that cools the power electronics and the power module (IPM) in the outdoor unit has gone above its safe temperature. The unit stops the compressor to protect the inverter board, may restart once it cools, and then stop again. The same code can mean something else on other brands, and wall-mounted Mitsubishi Electric models show errors as lamp blinks with a different meaning.

Models covered: Mitsubishi Electric ducted, ceiling and cassette units (Mr. Slim) with check codes on the wired remote; wall-mounted Mitsubishi Electric models may show errors as lamp blinks with a different meaning.

Symptoms4

The outdoor unit stops in the hot midday hours and U5 appears.
The unit works normally at night but stops during the day.
The outdoor fan does not turn or turns slowly.
Weak cooling before the stop, with very hot air around the outdoor unit.

Possible causes5

Dust covering the condenser and heat sink, preventing the electronics from cooling.
A failed or weak outdoor fan.
The outdoor unit installed in an enclosed space or full sun with hot air recirculating.
High operating pressure from a dirty condenser or overcharge increasing inverter load.
Poor thermal contact between the power module and heat sink, or a faulty heat sink sensor or board.

How to diagnose5

Turn the unit off at the breaker and let it cool before restarting.
Make sure the outdoor unit has enough clearance and the condenser is not blocked by dust or objects.
Switch off at the breaker before opening any panel; the outdoor unit and its inverter board keep a dangerous charge for a while after switch-off.
The technician checks the outdoor fan, the heat sink condition and how the power module is mounted on it.
The technician compares the heat sink sensor reading with the real temperature and measures operating pressures against the manufacturer specification.

How to fix6

Carefully wash the condenser and heat sink with power off, protecting the board from water.
Repair or replace the outdoor fan motor.
Improve the outdoor unit location or shade it without blocking airflow.
Replace the heat sink thermistor if its reading is wrong.
Replace the outdoor inverter board if it is proven faulty.
Run the unit in hot conditions, monitor temperatures and confirm the code does not return.

Repair cost

0–200

200–600

600–1,500

1,500+

In Saudi riyals; the highlighted part is the expected range for this fault.

The cost is low when washing and better ventilation solve it, and rises for an outdoor fan motor or an inverter board.

Prices are rough estimates including the part and the technician’s fee, and vary with brand, model and part source.
Prices last updated: September 2026

Frequently asked questions

Why does it run at night but stop by day?

Midday heat plus a dirty condenser or weak fan pushes the heat sink over its limit, while cooler night air keeps it within range.

Does shading the outdoor unit help?

Yes, if the shade is high and does not block air in or out; covering or boxing in the unit makes the problem worse.

Is U5 harmful to the unit?

The code itself is a protection, but repeated events stress the inverter board and power module, some of the most expensive parts, so fix the cause quickly.

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This guide is for information only and does not replace an inspection by a qualified technician. If the fault involves brakes, steering, engine temperature, electrics or refrigerant, do not attempt the repair yourself.

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