Abnormal High Pressure (63H Operated)

What it means

This code appears on the wired remote of Mitsubishi Electric Mr. Slim ducted, ceiling and cassette units. It means the high-pressure switch 63H in the outdoor unit has opened because discharge refrigerant pressure went above the safe limit. The unit stops the compressor at once to protect it, may try again, and locks out with the code if the high pressure repeats. 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.

Related codes: U8U5UPP6

Symptoms4

• The outdoor unit stops suddenly in the hottest hours and U1 appears.
• Weak cooling before the stop, with very hot air from the outdoor unit.
• The outdoor fan does not turn or turns slowly.
• Repeated stops shortly after each restart.

Possible causes7

• A condenser clogged with dust and sand, very common in Saudi conditions.
• A failed or slow outdoor fan.
• Poor ventilation around the outdoor unit or hot air recirculating in a tight space.
• A closed service valve or a restriction in the refrigerant circuit.
• Refrigerant overcharge or air in the system after incorrect charging.
• In heating, clogged indoor filters or a weak indoor fan.
• A faulty 63H switch or its connector (less common).

How to diagnose5

1. Turn the unit off at the breaker and wait until the outdoor unit cools before restarting.
2. Look at the condenser: heavy dust or nearby obstructions are the strongest suspects.
3. Make sure there is enough clearance around the outdoor unit and that hot discharge air is not coming back into it.
4. The technician checks the outdoor fan and motor and confirms the service valves are open.
5. The technician measures operating pressures against the manufacturer specification, then checks the 63H switch and connector if pressures are normal.

How to fix6

1. Wash the condenser and outdoor unit thoroughly and clear obstructions around it.
2. Repair or replace the outdoor fan motor.
3. Improve the outdoor unit location or fit a baffle to stop hot air recirculation.
4. Open the service valves or clear the restriction in the circuit.
5. Have a licensed technician recover, evacuate and recharge by weight if the system is overcharged or contains air.
6. Replace the 63H switch if proven faulty, then run in hot conditions and confirm the code does not return.

Repair cost

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

Washing the outdoor unit is the cheapest and most common fix; the cost rises for an outdoor fan motor, charge correction or an outdoor 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