- HVAC
- Air conditioner
P8
Mitsubishi Electric P8 on an air conditioner: pipe temperature out of range
Risk level
High
Professional inspection is recommended.
Urgency
Medium
Quick answer
On Mr. Slim PKA wall units, P8 means the indoor pipe temperature does not reach the expected range in cooling or heating. If the unit was just installed, call the installer; otherwise call a technician. Do not touch the valves or refrigerant.
Safety first
Stop and check this first
- Mitsubishi Electric requires all supply circuits to be disconnected before reaching the terminals. If refrigerant leaks, ventilate the room: in contact with a flame it releases toxic gases. Board, wiring and refrigerant circuit are technician work.
- Mitsubishi states this unit uses R410A only. Do not accept a top-up with another gas or without a leak search.
Safe checks you can perform
- Mode and timing of the code
- Recent installation or relocation
- Comparing pipe and room temperature
Leave these tasks to a qualified professional
- Do not attempt this professional task: Check stop valves and sensor before adding refrigerant
- Do not attempt this professional task: Leak search and certified recharge
What a technician must be able to justify
Technician visit
These are the steps they must carry out and show you. Tick them as they work: if steps are skipped, do not accept a part swap.
These are not instructions for opening or handling the equipment yourself. They are the checks that should support a technical conclusion.
Check stop valves and sensor before adding refrigerant
What they doThe technician confirms the stop valves are fully open and the pipe sensor is firmly held before touching the charge.
They must show youthe pipe and room temperature readings.
In writingthe state of the valves and the sensor.
Leak search and certified recharge
What they doIf refrigerant shortage is suspected, the technician finds and repairs the leak and charges only R410A under an F-gas certificate.
They must show youwhere the leak was.
In writingamount charged, refrigerant type and certificate number.
Before accepting a part or repair
Nothing has been shown yet. Do not accept a part swap based on the code alone.
Follow these steps
Note: Follow the documented order. An error code identifies the affected system, but it does not prove by itself which part has failed.
Mode and timing of the code
- Who:
- you.
- How:
- note whether P8 appears in cooling or heating and how long the unit had been running.
- Result that matters:
- Mitsubishi needs at least 9 minutes in cooling and 27 in heating to detect it, and never flags it in drying mode.
- If it appears in drying mode:
- it is not P8 according to the maker; recheck the code you read.
- If it appears after a while in cooling or heating:
- it fits P8 detection; continue with the checks.
- Evidence to keep:
- a note with mode, start time and time of the code.
Evidence: Mitsubishi Electric split-system heat pump service manual OCH639, indoor units PKA-A24KA7, PKA-A30KA7, PKA-A36KA7
Recent installation or relocation
- Who:
- you.
- How:
- check whether the unit was installed, moved or had refrigerant work shortly before P8 appeared.
- Result that matters:
- whether the fault started right after an intervention.
- If it matches a recent installation:
- call the installer; a stop valve not fully opened is a cause Mitsubishi lists.
- If the unit had run well for a long time:
- the valve is less likely and refrigerant shortage or the sensor gain weight.
- Evidence to keep:
- the installation invoice or job sheet with its date.
Evidence: Mitsubishi Electric split-system heat pump service manual OCH639, indoor units PKA-A24KA7, PKA-A30KA7, PKA-A36KA7
Comparing pipe and room temperature
- Who:
- an F-gas certified air conditioning technician.
- How:
- compares pipe temperature with room temperature using the remote in service mode, switch SW2 on the outdoor board or the PAC-SK52ST tool.
- Result that matters:
- whether the pipe cools or warms as it should with the compressor running.
- If the pipe barely changes:
- it points to a closed valve, refrigerant shortage or the circuit; continue with a leak check.
- If the pipe changes but the reading does not:
- it points to the sensor or its holder.
- Evidence to keep:
- a job sheet with the readings and the method used.
Requires access to the outdoor board and, for any refrigerant work, an F-gas certificate: technician only.
Evidence: Mitsubishi Electric split-system heat pump service manual OCH639, indoor units PKA-A24KA7, PKA-A30KA7, PKA-A36KA7
Still not solved
If the error persists, stop here. See what the technician must do and show you.
Where this code applies
A code is meaningful only inside the right product and version context.
Primary scope
- System
- HVAC
- Brand
- Mitsubishi Electric
- Product type
- Air conditioner
Known code variants
- Mitsubishi P8
- Mr. Slim P8
- PKA P8
What it means
Mitsubishi Electric defines P8 as a pipe temperature error. In cooling it is detected when the pipe is not in range 3 minutes after the compressor starts and stays out for 6 more minutes (at least 9 minutes in all); in heating, when it is not in range within 20 minutes. It is not detected in drying mode or during defrost. It can come from a loose pipe sensor, refrigerant shortage, a stop valve not fully opened or a refrigerant circuit fault: the code does not say which.
Warnings and stop conditions
- Highsource verified
Mitsubishi Electric requires all supply circuits to be disconnected before reaching the terminals. If refrigerant leaks, ventilate the room: in contact with a flame it releases toxic gases. Board, wiring and refrigerant circuit are technician work.
Evidence: Mitsubishi Electric split-system heat pump service manual OCH639, indoor units PKA-A24KA7, PKA-A30KA7, PKA-A36KA7
- Mediumsource verified
Mitsubishi states this unit uses R410A only. Do not accept a top-up with another gas or without a leak search.
Evidence: Mitsubishi Electric split-system heat pump service manual OCH639, indoor units PKA-A24KA7, PKA-A30KA7, PKA-A36KA7
Symptoms and causes
Probable causes · in order
- Stop valve not fully openedPossible
Typical after a recent installation or relocation: the unit never reaches the expected pipe temperature from its first use.
Evidence: Mitsubishi Electric split-system heat pump service manual OCH639, indoor units PKA-A24KA7, PKA-A30KA7, PKA-A36KA7
- Refrigerant shortage or circuit faultPossible
Mitsubishi lists refrigerant shortage and refrigerant circuit defects; only an F-gas certified technician can confirm it and recharge.
Evidence: Mitsubishi Electric split-system heat pump service manual OCH639, indoor units PKA-A24KA7, PKA-A30KA7, PKA-A36KA7
- Loose pipe sensor or small temperature differencePossible
If the pipe thermistor holder has come off, or the room is already close to the pipe temperature, the reading does not change enough even with a sound circuit.
Evidence: Mitsubishi Electric split-system heat pump service manual OCH639, indoor units PKA-A24KA7, PKA-A30KA7, PKA-A36KA7
- Crossed pipes on multi-unit installationsPossible
Mitsubishi cites reversed extension pipe connection when several units are connected; it only applies to those installations.
Evidence: Mitsubishi Electric split-system heat pump service manual OCH639, indoor units PKA-A24KA7, PKA-A30KA7, PKA-A36KA7
Virtual technician
Does P8 still appear after these checks?
Answer a few questions to narrow down the likely cause and the safest next action. Guidance only - it never replaces a professional.
Sources and technical references
- 1
Mitsubishi Electric · 2016 · manual
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