Mitsubishi P-codes and blinking lights — Indoor-unit fault family

What this error means

P-series codes (and equivalent indoor-unit LED blink patterns) are indoor-unit-detected faults: P1/P2 are thermistor (sensor) faults, P3 is a communication error, P4 is the float switch open, P5 the drain pump, and P6 freeze/overheat protection. The office classic is P4/P5 — the condensate drain system shutting the unit down before it leaks through the ceiling.

Symptoms

• P-number on controller or rhythmic blinking on the indoor unit
• Unit runs then stops repeatedly
• Water dripping from the indoor head (drain-related faults)

Try this first (safe DIY steps)

1. Record the exact code or count the blink pattern — it identifies the subsystem
2. Power cycle at the breaker for 3–5 minutes
3. If there's any water at the indoor unit, stop running it — that's a drain fault and continuing risks a ceiling leak
4. Clean/replace filters if airflow-related (dirty filters trigger temperature-protection stops)

Safety: power off before any physical intervention. Never bypass covers or interlocks — fuser areas run hot enough to burn.

When to call a technician

Any recurring P-code — refrigerant, pressure, and drain-pump work is licensed-tech territory.