This guide shows how to reset a Mitsubishi air conditioner safely. Before you reset anything, there is something to settle. Australia has two completely separate Mitsubishi air conditioning companies, and they are not the same business. Mitsubishi Electric is one. Mitsubishi Heavy Industries is the other.
Their reset procedures differ, their indicator lights mean different things, and one of them has a button that will put your unit into a service mode if you hold it too long. Working out which you own takes ten seconds and saves a lot of confusion.
Which Mitsubishi do you have?
Look at the badge on the indoor or outdoor unit. Mitsubishi Electric units say Mitsubishi Electric. Mitsubishi Heavy Industries units say Mitsubishi Heavy Industries, often shortened to MHI, and the model number usually starts with SRK.
| What you want to do | Mitsubishi Electric | Mitsubishi Heavy Industries |
|---|---|---|
| Run the unit without a remote | Emergency operation switch. Press to cycle. | Unit on and off button. Press once. |
| Reset the remote | RESET button, pressed with a thin instrument. | ACL switch, pressed with a pen tip. |
| What the remote reset clears | Not published. | Everything. It returns to the initial state and clears the weekly timer. |
| Danger of holding the unit button | None documented. It works on presses. | Five seconds or more sets forced cooling for servicing. |
| Blinking operation lamp on a wall split | Normal. It is close to the set temperature. | Depends on the blink pattern. |
| Power timing | Ducted units need power on 12 hours before use. | Wait at least 5 minutes after stopping before cutting power. |
Neither company puts a button marked reset on the indoor unit. If you are looking for one, it does not exist. What each has instead is described below.
Mitsubishi Electric
The emergency operation switch
When the remote cannot be used, Mitsubishi Electric documents an emergency operation switch on the indoor unit, usually shortened to E.O. SW.
Each press moves it through emergency cooling, then emergency heating, then stop. While it runs the settings are fixed. The temperature is 24 degrees, the fan speed is medium, and the horizontal vane is on auto.
One detail worth knowing before you panic at the result. Mitsubishi Electric states that the first 30 minutes of operation is a test run, during which temperature control does not work and the fan speed is set to high. A unit roaring away and ignoring the room is behaving as documented.
This is a bypass, not a reset. It does not clear anything.
Resetting the remote
There is a RESET button on the remote, pressed gently with a thin instrument. Mitsubishi Electric is unusually direct about why it matters. Its manual states that if the RESET button is not pressed, the remote controller may not operate correctly.
So the order after a battery change is fit the batteries, then press reset. Skipping the second half is a common reason new batteries appear not to have helped.
On batteries, Mitsubishi Electric documents AAA alkaline cells inserted negative pole first, and is specific about what not to use. No manganese batteries, no leaking batteries, no rechargeable batteries, and replace all of them with new ones of the same type.
The low battery warning matters too. Once the battery replacement indicator lights up, the remote stops working in about seven days.
Resetting the filter indicator
On a wall split there is nothing to reset. Mitsubishi Electric does not document a filter indicator lamp or a filter reset on its wall mounted models at all. Those manuals give a cleaning schedule instead.
On a ceiling cassette with a wired controller it is documented. The filter sign appears on the main display when cleaning is due. From the main menu select Filter information, follow the prompt that tells you to press the reset button after cleaning, and confirm when it asks whether to reset the filter sign.
Power resetting at the breaker
Mitsubishi Electric documents turning the breaker off and on as the fix for one specific symptom, where the horizontal vanes are out of position. Turn the breaker off and on, then make sure the vanes move to the correct close position. When power returns, the vane position resets over about a minute before operation starts.
No wait time between off and on is published for wall splits, and this page will not invent one. The only enforced delay is the three minute restart protection.
Ducted systems are completely different and this matters. Mitsubishi Electric states you must turn on the power at least 12 hours before starting operation, and warns that starting operation immediately after turning on the main power switch can result in severe damage to internal parts. It also says to keep the power switch on during the operational season.
So if somebody has switched a Mitsubishi Electric ducted system off at the switchboard for the winter, do not simply flick it on and run it. Give it the twelve hours.
What the lights mean on a Mitsubishi Electric wall split
This is the most useful thing on the page, because it contradicts what most people assume.
- Lit. The unit is operating to reach the set temperature, about two degrees or more away from it.
- Blinking. The room temperature is approaching the set temperature, about one to two degrees from it.
- Not lit. Standby mode, only during multi system operation.
A blinking operation lamp on a Mitsubishi Electric wall split is good news. It means the unit is nearly there.
Cassette and ducted units are the opposite. Mitsubishi Electric states that if the operation lamp near the receiver is blinking, the unit needs to be inspected. Same company, similar looking light, opposite meaning.
Mitsubishi Heavy Industries
The unit button, and the mistake to avoid
MHI puts a unit on and off button on the indoor unit for when the remote is not available. Press it and the unit starts. Press it again and it stops.
Here is the part worth reading twice. MHI states you should not keep the button pressed down for 5 seconds or more, because pressing it for 5 seconds or more sets the forced cooling operation used during servicing or when relocating the air conditioner.
That is a real explanation for a genuinely baffling complaint. If an MHI unit is stuck blowing cold air and ignoring the remote, somebody may simply have held that button too long. It is not a fault. It is a service mode.
The ACL switch
MHI uses an ACL switch rather than a button marked reset. When the display shows any abnormal condition, press the ACL switch with the tip of a ballpoint pen.
MHI is also clear about what you lose, which most brands are not. When the battery is replaced or the ACL switch is pressed, the remote is set to the initial state, and since the weekly timer program is not set in the initial state you have to program it again.
So if you use the weekly timer on an MHI, write the program down before you touch the ACL switch.
Power timing on an MHI
MHI documents the wait on the way off rather than the way on, and gives a reason. Do not shut off the power source immediately after stopping the operation. Wait at least 5 minutes, otherwise there is a risk of water leakage or breakdown.
That is the opposite of how most people switch a unit off at the wall, and worth passing on to anybody who kills the power the moment the unit stops.
What the blinking lights mean on an MHI
MHI encodes far more in its lights than Mitsubishi Electric does, and the blink pattern is the message. The RUN light is green and the TIMER light is yellow.
- Steady RUN light. The unit is operating.
- Slow blink, roughly 1.5 seconds on and half a second off. Airflow is held back to prevent blowing cold air in heating. Not a fault.
- Blink of roughly 3 seconds on and 1 second off. Self clean operation is running. Not a fault.
- Fast blink. Invalid operation mode, usually a mode clash on a multi system rather than a hardware problem.
- Steady TIMER light. A timer is set. Not a fault.
One honest caveat. These timings differ between MHI model series. On another series the 1.5 second pattern means defrosting and the 3 second pattern means hot keep. Check the manual for your model rather than treating any one table as universal.
Error codes on an MHI, and why no table appears here
MHI Australia confirms the mechanism plainly. Its split systems use a sequence of flashes on the run light and timer light to display error codes.
The self diagnosis function exists on every MHI wall split. What does not exist is a single reliable published table, because the mapping differs between model series and the tables sit inside model specific manuals.
For that reason this page does not print an MHI code table. Count the flashes on the run light and the timer light, write both down, and quote them when you call. A wrong code table is worse than none.
Mitsubishi behaviour that looks like a fault and is not
The three minute wait
Mitsubishi Electric states the unit cannot be operated for about 3 minutes when restarted, and that this protects the unit according to instructions from the microprocessor. MHI blocks restart for 3 minutes after you stop it, with the run light still on.
No warm air at the start of heating
Mitsubishi Electric simply says to wait as the unit is preparing to blow out warm air. MHI is more specific. Airflow has stopped to prevent blowing out cold air until the indoor heat exchanger has warmed up, which takes 2 to 5 minutes, and the run light blinks slowly while it happens.
Defrost
Mitsubishi Electric documents heating stopping for about 10 minutes, completed in a maximum of 10 minutes, when the outside temperature is low and humidity is high. MHI gives 5 to 15 minutes, again with the run light blinking slowly, and notes water or steam may escape from the outdoor unit.
The fan slowing or stopping
Mitsubishi Electric documents that in heating, if the airflow temperature is too low or defrosting is happening, the horizontal vane goes to horizontal, the fan speed decreases and the fan may stop. On its cassettes, when the set room temperature is reached in cooling the fan runs at the lowest speed rather than stopping.
MHI documents the indoor fan stopping in dry mode to prevent re evaporation of dehumidified moisture and to save energy.
The unit started by itself
Mitsubishi Electric fits auto restart. When the main power is turned off without stopping the unit with the remote and is turned on again, the unit starts automatically in the same mode it was in before. That is a feature, not a ghost.
Why does my Mitsubishi keep turning itself off?
- A timer. On an MHI a steady yellow timer light means one is running.
- Defrost. Up to 10 minutes on Mitsubishi Electric, 5 to 15 on MHI.
- Multi split standby. On a Mitsubishi Electric multi system, an unlit operation lamp means that indoor unit is in standby because another is calling a conflicting mode.
- Self clean on an MHI. The unit appears to run on after you stop it, then stops itself.
- Forced cooling on an MHI, if somebody held the unit button for five seconds or more.
- Demand response. Mitsubishi Electric states on its Australian product pages that the outdoor unit includes a demand response enabling device, allowing your electricity provider to control the system at three preprogrammed modes at times of peak demand. A system throttled by the network feels exactly like a fault.
When a reset is not the answer
- A blinking operation lamp on a cassette or ducted receiver, which Mitsubishi Electric documents as needing inspection.
- A repeating flash sequence on an MHI run and timer light that returns after a power cycle.
- The same fault returning within hours of every reset.
- Water appearing below the indoor unit.
- A burning smell. Stop the unit and switch it off at the breaker.
- The breaker tripping every time you restore power.
Getting a Mitsubishi back without breaking anything
There is no reset button on either brand, and that is the useful thing to know. There is an emergency switch, a pinhole on the remote, a breaker, and on the Heavy Industries side a button that must not be held for five seconds.
Work out which Mitsubishi you have first, match the reset to the problem, and give the unit three minutes before deciding anything. If the symbols on your remote are the puzzle rather than the unit, our guide to Mitsubishi air conditioner symbols covers those.
When a reset only buys you a few days, that is the point where guessing costs more than asking. We send a licensed technician who works on Mitsubishi split, multi head and ducted systems across Melbourne, and the price is confirmed before any work starts. It is also worth knowing how often you should service your air conditioner, since clean filters remove a good share of the reasons people reset in the first place.
A system that needs resetting regularly is usually overdue for maintenance, and our guide on how often to service a Mitsubishi air conditioner gives the interval.
For a fault that returns after the reset, our Mitsubishi air conditioning service covers split and ducted systems across Melbourne, and you can request a quote with the code in hand.
For general advice on staying safe around electrical appliances at home, see Energy Safe Victoria.
Reviewed by AC repair and service specialist on 22 October 2026. How we write our articles