A1Fujitsu · ASTG09 / ASTG12 / AOTG09 / AOTG12 KMTC · Mini Split

Fujitsu ASTG09 / ASTG12 / AOTG09 / AOTG12 KMTC error code A1

Discharge temperature error, compressor over-temperature

Needs attention soon

Also written as A1, discharge over-temperature, compressor too hot, code A1

Which models this applies to. This page covers the Fujitsu GENERAL AIRSTAGE KMTC wall split codes, indoor and outdoor.

What is specific to the ASTG09 / ASTG12 / AOTG09 / AOTG12 KMTC platform

ASTG09KMTC and ASTG12KMTC indoor units with AOTG09KMTC and AOTG12KMTC outdoor units on R32. A compatible non-polar wired controller shows the code directly on its display. The supplied wireless controller has no screen and shows the same codes as a flashing pattern on the indoor indicator lamps instead. The service reference gives a separate main PCB, control unit and inverter assembly identification for each of the two capacities, so a board from the wrong capacity is a recognised cause of codes 32 and 62.

Your control board prints the code as text, for example F01 or EE3, so you read it off the display rather than counting blinks. The printed number is the fault itself, not a position in a table.

Quick answer

On Fujitsu ASTG09 / ASTG12 / AOTG09 / AOTG12 KMTC, A1 is a fault. It means discharge temperature error, compressor over-temperature. A first thing to check: A refrigerant charge that is too low, so the compressor runs without enough refrigerant to cool its windings.

Applies to: Fujitsu ASTG09 / ASTG12 / AOTG09 / AOTG12 KMTC; Fujitsu GENERAL AIRSTAGE KMTC wall split codes, indoor and outdoor · Mini Split
Type of code: Fault; Urgency: Needs attention soon
First safe check: Confirm the outdoor fan is running at full speed, since a condenser that cannot reject heat is the most common underlying cause.

Checked 2026-09-26

What A1 means on this model

The compressor discharge temperature has genuinely run too high and the unit has stopped to protect itself. This is a real over-temperature condition rather than a failed sensor, and it is the fault that destroys compressors when it is ignored. The causes sit in the refrigerant circuit, the charge, the electronic expansion valve, and the condenser, and the measured or verified item on this platform is the expansion valve coil, which has its own resistance value of 46.0 Ohm at 20 C. Keep this separate from code 71, which is a failed discharge temperature sensor producing a similar stop.

Symptoms you will notice

Code A1 and the system stops
The system runs for a while then stops, and may restart and stop again
The discharge pipe is extremely hot
The system never reaches set temperature in either mode

Common causes

The code tells you what the control detected, not which part failed. These are the causes we see most often, roughly in order of likelihood:

A refrigerant charge that is too low, so the compressor runs without enough refrigerant to cool its windings
An electronic expansion valve that is not metering correctly
A condenser that is not rejecting heat, so head pressure climbs
A failed or slow outdoor fan motor
A dirty outdoor coil or blocked airflow
A failing compressor
A non-condensing condition such as snow on the outdoor coil

What you can safely check

These are homeowner-level checks. None of them need you to open a live electrical compartment or work on gas.

Confirm the outdoor fan is running at full speed, since a condenser that cannot reject heat is the most common underlying cause.
Check the outdoor coil is clean and the unit has clear discharge airflow.
Measure the expansion valve coil and compare it with the documented 46.0 Ohm at 20 C, which is the documented check on this circuit.
Inspect the refrigerant lines for oil staining or a frost patch, which points at a leak.

Do not do these

×Do not add refrigerant without measuring the actual charge. Low charge is one cause of this code, not the only one.
×Do not keep restarting. Sustained discharge over-temperature destroys compressor windings, and this protection exists to stop exactly that.
×Do not work on the refrigerant circuit without recovery equipment and the procedures appropriate for R32.

When to call a technician

Book a technician, do not keep resetting it

This fault will not clear on its own. Every power cycle gives the control one more failed attempt, and repeated attempts are what turn a cheap part replacement into a seized or contaminated system.

The refrigerant circuit is sealed and legally requires licensed handling. Opening it without certification releases refrigerant and can put the whole system in violation of regulation, so a low-pressure or high-pressure fault on this equipment is a call-out, not a weekend job.
If the appliance has stopped mid-cycle, is making a noise you have not heard before, or smells burnt, stop reading here and call. Those are symptoms of something the fault code does not describe well enough.

Checking that the outdoor fan runs and the coil is clear is reasonable for a homeowner. Charge and valve work is a licensed technician job.

What it costs to fix

Parts

Expansion valve $200 to $500. Compressor $1,400 to $3,000. Outdoor fan motor $300 to $700. Discharge sensor $30 to $90.

Labor

Three to six hours depending on the cause.

DIY or technician