Mitsubishi Electric AC Error Code P8 — High Discharge Temperature

What Does This Error Mean?

P8 on a Mitsubishi Electric AC means the discharge pipe thermistor has detected that the temperature of the refrigerant leaving the compressor is dangerously high. The system shuts down to protect the compressor from overheating damage. Common causes include low refrigerant, a blocked outdoor coil, or extreme ambient temperature.

Affected Models

Mitsubishi Electric MSZ-AP Series
Mitsubishi Electric MSZ-EF Series
Mitsubishi Electric MSZ-GL Series
Mitsubishi Electric MSY Series
Mitsubishi Electric Inverter Split AC (all models)

Common Causes

Low refrigerant — insufficient refrigerant causes the compressor to run hot
Condenser coil blocked with dust or debris — heat cannot be rejected effectively
Outdoor fan not spinning — heat builds up around the condenser and compressor
Very high outdoor ambient temperature pushing the system beyond design limits
Refrigerant overcharge — incorrect refrigerant levels alter operating pressures
Discharge pipe thermistor faulty — triggering P8 at normal temperatures

How to Fix It

Switch off the AC immediately.

Do not attempt more than one restart while P8 is active — you risk permanently damaging the compressor.
Go outside and inspect the outdoor unit.

Check that the outdoor fan is spinning and that nothing is blocking the airflow in or out of the unit. Clear any debris, leaves, or objects within 50 cm of the unit.
Check the outdoor condenser coil for blockage.

The aluminium fins on the outdoor unit should be visible and relatively clean. If they are heavily clogged with dust or cottonwood seeds, gently rinse with a garden hose (power off) to improve airflow.
After clearing any visible blockage, attempt one restart and monitor.

If P8 clears and the AC runs normally, the blockage was the cause. If P8 returns within 15 minutes, call a Mitsubishi Electric technician — the refrigerant level or thermistor needs professional inspection.

When to Call a Professional

P8 requires a licensed HVAC technician. Do not restart the AC repeatedly — running the compressor at extremely high discharge temperatures causes permanent compressor damage. A technician will check refrigerant levels, condenser condition, and thermistor readings.

Frequently Asked Questions

Can P8 damage my Mitsubishi compressor permanently?

Yes — if ignored and the AC is repeatedly restarted while P8 is active, the compressor can be permanently damaged by overheating. Compressor replacement is the most expensive AC repair, often costing more than a new unit. The P8 shutdown is protecting you from that cost — do not override it.

Does P8 always mean low refrigerant?

Not always — P8 can be caused by a blocked condenser or failed outdoor fan without any refrigerant issue. Check the outdoor unit condition first before assuming you need a refrigerant top-up. Only a technician with pressure gauges can accurately determine refrigerant levels.