Mitsubishi Heavy Industries Refrigerant Code
Mitsubishi E57 Error Code
The Mitsubishi E57 error code is a Mitsubishi Heavy Industries alarm that points to refrigerant not flowing properly. In most cases, the charge is low or a service valve is restricting flow. It is not a Mitsubishi Electric code. Read on to understand what triggers it, what you can safely do, and how a licensed technician fixes it.
Meaning
What Is E57 on a Mitsubishi Heavy Industries System?
MHI documentation describes E57 a little differently across its ranges, but the message is consistent. On wall splits, it is refrigeration cycle protective control. On packaged and ducted ranges, the manuals call it insufficient refrigerant or detection of a closed service valve. On multi splits, it is refrigerant cycle protection.
In everyday terms, the system has noticed that the indoor coil is not cooling the air as much as it should. The most likely explanations are that refrigerant has leaked out, or that a valve is stopping it from circulating. Either way, the board stops the system before running short damages the compressor.
This makes E57 one of the more important MHI codes to act on. A refrigerant problem rarely fixes itself, and running a system short of gas can lead to larger faults later.
Maker
Mitsubishi Heavy Industries. Mitsubishi Electric does not use E57 with this meaning and reports refrigerant related problems through other codes.
Main Cause
Low refrigerant charge from a leak, or a service valve that is closed or only partly open.
Effect
The system stops on first detection to protect the compressor. Cooling and dry modes are where it is usually found.
Detection
How Does an MHI Unit Decide to Show E57?
The detection method is clever. The indoor unit compares two temperatures: the indoor heat exchanger and the return air coming into the unit. In cooling, a healthy coil should be much colder than the air passing over it.
If the coil is barely colder than the return air, the board concludes that refrigerant is either missing or blocked. MHI documentation notes this check runs at the first cooling or dry start after power on. When the condition is detected, the unit stops straight away.
This explains a common owner experience. The system may seem fine in heating through winter, then show E57 on the first warm day you switch to cooling. The fault was likely present for some time, but the check only ran when cooling began.
Spotting It
How Will E57 Appear on My System?
On MHI wired controllers, E57 appears on screen when the system stops. Touch screen RC-EX controllers may show a protective stop message with the code, and the operation lamp can change colour. Older RC-E controllers display the code and the indoor unit address.
Wall splits often use lamp patterns instead. For some SRK ranges, the user manuals describe seven flashes of the RUN light, with the TIMER light on, as a refrigerant insufficient signal. Your model may differ, so count carefully and check the manual if you have it.
Either way, write down exactly what you see, including any unit address. Note also whether the system had just been switched to cooling for the first time in a while. That detail fits the way E57 is detected.
Causes
What Are the Usual Causes of an MHI E57?
MHI documentation separates E57 causes into installation issues and operating issues. Both are worth understanding.
Installation Causes
- A service valve left closed or only partly opened after installation.
- An incorrect refrigerant charge for the length of pipe run.
- A loose sensor connector giving a misleading reading.
- Joints made poorly during installation, leading to a slow leak.
Operating Causes
- Refrigerant loss from a leak at a joint, flare nut or coil.
- A faulty indoor heat exchanger thermistor.
- A faulty return air thermistor.
- A defective indoor control board, usually considered last.
Notice that sensor faults appear on the list. Because E57 is judged by comparing two sensors, a failing sensor can trigger it even when the refrigerant is fine. That is why a technician checks sensors before assuming a leak.
Owner Steps
What Can I Safely Do When E57 Appears?
E57 is almost always a technician job. Even so, a few safe checks help rule out simple contributors and give useful information.
- Stop the system and note the code, unit address and time.
- Clean the indoor filters, since heavy dust can affect coil performance and sensor readings.
- Check that indoor return grilles are not blocked by furniture.
- Clear the outdoor unit of debris so airflow is not a confusing factor.
- From a safe distance, look for oily marks under outdoor pipe joints, which can hint at a leak.
- Note any recent installation, relocation or refrigerant work.
Please do not open service valves, use a refrigerant top up can, or remove any covers. Refrigerant handling in Australia legally requires an ARCtick licence. Incorrect handling can injure you and damage the system.
Repair
How Does a Technician Fix an MHI E57?
A licensed technician works through E57 in an order that rules out quick fixes before refrigerant work. That avoids unnecessary gas handling and cost.
Check the Valves
They confirm both service valves at the outdoor unit are fully open. A partly closed valve is a quick fix if found.Inspect Sensor Connections
The connectors for the indoor heat exchanger and return air thermistors are checked and reseated.Test the Sensors
Both thermistors are measured against their expected values and replaced if out of range.Measure Pressures
Gauges are connected to assess the operating pressure and refrigerant charge. This step requires an ARCtick licence.Find and Fix the Leak
If the charge is low, the technician locates the leak, repairs it, then evacuates and recharges to the correct amount.Consider the Board
Only if all of the above check out does the indoor control board become the suspect.
The key point is that refrigerant is never simply topped up without finding the cause. Refrigerant does not wear out. If it is low, it has escaped, and the leak must be fixed for a lasting repair.
Risk
Can I Keep Running an MHI System With E57?
No. The system stops itself, and that is the correct response. Running a system short of refrigerant forces the compressor to work without enough cool returning gas. Over time, that causes overheating and wear.
In fact, E57 can be an early warning for more serious faults. A system that continues to lose charge may eventually trip on compressor protection codes such as E36. Dealing with E57 promptly is the best way to avoid that path.
If you rely on heating, the system may appear to work in heating mode for a while. Still, the leak continues. Book a repair rather than waiting for summer.
Climate
Why Do Refrigerant Leaks Happen in Australian Homes?
Australian conditions are tough on refrigerant circuits. Salt air in coastal suburbs of Sydney, Perth, Adelaide, Melbourne and Brisbane slowly corrodes outdoor coils. Over years, tiny pinholes can form in the copper or aluminium, and refrigerant escapes gradually.
Heat cycling is another factor. Pipe joints expand and contract daily through long hot summers. A flare connection that was marginal at installation may eventually start to weep. Vibration from the outdoor unit adds stress over time too.
Storms can play a part when they shift outdoor units on brackets or slabs. Movement stresses the pipework. If E57 appeared soon after a storm, check from a distance whether the outdoor unit looks displaced, and mention it when booking.
New Systems
Why Would a New MHI System Show E57?
It happens more than people expect, and it usually points to installation.
Valves Not Opened Fully
Outdoor units ship with refrigerant held behind service valves. If they are not opened fully at installation, flow is restricted, and the coil cannot cool properly.
Charge Not Adjusted
Longer pipe runs often need additional refrigerant. If the charge was not adjusted to suit the installation, the system may run short from day one.
Joint Leaks
A poorly made flare can leak slowly. The system may run well for weeks before enough refrigerant escapes to trigger E57.
If your system is new, contact the installer first, as the fault may be covered under their workmanship. Otherwise, we can book an independent technician.
Warning Signs
Did My System Give Warnings Before E57?
Often it did, though the signs are easy to miss. Refrigerant usually leaks slowly. As the charge drops, performance fades bit by bit rather than all at once. Owners tend to adapt without noticing until the code finally appears.
- Cooling took longer each week to bring the house down to temperature.
- Air from the vents felt cool rather than properly cold.
- The outdoor unit ran for long stretches without easing off.
- Frost formed on the thinner outdoor pipe or service valve.
- Power bills crept up through summer without a change in use.
- A faint hissing sound came from near a joint, either indoors or outdoors.
None of these signs alone proves a leak. Dirty filters and blocked outdoor coils can cause similar symptoms. However, if you noticed several of them before E57 appeared, tell the technician. It helps them estimate how long the system has been losing charge.
For the future, an annual service is a good way to catch a slow leak early. A technician who records how the system performs at each visit can spot a gradual decline long before it triggers a code. Early repair is usually simpler, and it protects the compressor from months of running short.
Ducted systems deserve extra attention here. Because the indoor unit is hidden in the roof, a leak at an indoor joint can go unnoticed for a long time. Regular checks of both halves of the system make that far less likely.
Before and After
What Should I Expect After an E57 Repair?
Once the cause has been fixed, the system should cool strongly again. Air from the indoor unit will feel noticeably colder, and the room should reach its set temperature faster than before the fault.
Ask the technician to explain where the leak was, how it was repaired and how much refrigerant was added. Keep that record. If the system ever loses performance again, it helps the next technician understand the history.
Over the following weeks, keep an eye on performance. If cooling fades again, call promptly. A second leak, or an incomplete repair, is far easier to deal with early than after the charge has dropped a long way.
Related Codes
Which Mitsubishi Codes Relate to E57?
E57 links to other refrigerant and temperature codes on both Mitsubishi brands.
MHI E36
Compressor overheat or high discharge temperature, often a later stage of refrigerant shortage.
Mitsubishi Electric P8
The other maker’s pipe temperature error, with a similar detection idea.
All Mitsubishi Codes
Browse every confirmed Mitsubishi Electric and MHI code we cover.
For other brands, see the main error codes library.
Book a Technician
How Do I Get an E57 Repair Booked?
Rapid Air Cooling handles the booking and sends an independent licensed technician to your home. We are not a Mitsubishi Heavy Industries dealer and do not claim manufacturer accreditation. Refrigerant work is done only by ARCtick licensed technicians.
Choose your city. In Sydney, use air conditioner repairs Sydney. In Melbourne, use Melbourne repairs. Brisbane owners can use Brisbane repairs and Mitsubishi in Brisbane. Perth owners can use Perth repairs, and Adelaide owners can use Adelaide repairs and Mitsubishi in Adelaide.
Read more about both makers on our Mitsubishi air conditioning page, browse the troubleshooting guides, or learn about our air conditioning service Australia wide.
Good to Know
What Finer Points Help With E57?
Open more detail
Because E57 relies on comparing coil and return air temperatures, very dirty filters or a blocked coil can sometimes confuse the reading. Cleaning filters before the technician arrives removes that variable. It will not fix a genuine leak, but it helps the diagnosis.
Leak detection takes skill. Technicians use pressure tests, electronic detectors and careful visual checks of joints, valves and coils. Some leaks are obvious, with oily residue around a flare nut. Others are tiny and need patient searching.
Refrigerant type matters for the repair. Newer MHI systems often use R32, while older ones may use R410A. The technician will use the correct refrigerant and recharge to the weight specified on the outdoor unit’s label, adjusted for pipe length where required.
Sensor faults can look like refrigerant faults with E57, which is why they are tested early. If the return air thermistor reads too cold, or the coil thermistor reads too warm, the board may see a small difference and assume refrigerant is missing. Replacing a faulty sensor in that situation clears E57 without any gas work at all. A careful technician confirms the sensors before connecting gauges.
Multi split systems add another layer. Each indoor unit has its own coil and sensors, yet they share refrigerant from one outdoor unit. If E57 shows on one head only, a local sensor or a restriction in that branch is possible. If several heads complain, a system wide shortage becomes more likely. Telling us which rooms are affected helps the technician plan the visit.
Finally, if a coil is badly corroded with several leaks, the technician may discuss whether coil replacement or system replacement makes more sense. They will lay out the options so you can choose.
Questions
Frequently Asked Questions
Is E57 a Mitsubishi Electric code?
No. E57 with this meaning belongs to Mitsubishi Heavy Industries. Mitsubishi Electric uses a different code system.
Does E57 always mean a gas leak?
Not always. A closed service valve or a faulty coil or return air sensor can also trigger E57. A technician checks these before assuming a leak.
Why did E57 appear on the first warm day?
The check runs at the first cooling or dry start after power on. A problem present through winter may only be detected when you switch to cooling.
Can I buy refrigerant and top it up myself?
No. Refrigerant handling in Australia requires an ARCtick licence. Topping up without fixing the leak will also bring E57 back.
My new system shows E57. Who should I call?
Contact the original installer first, as valve or charge issues may fall under their workmanship. If that is not possible, we can book a technician.
Will E57 damage my compressor?
The system stops to prevent damage. Repeatedly forcing it to run while short of refrigerant, however, can stress the compressor. Book a repair promptly.
How long does an E57 repair take?
A valve or sensor fix can be quick. Finding and repairing a leak, then evacuating and recharging, takes longer. The technician will explain once they have diagnosed it.
MHI System Showing E57?
Call us and we will book an ARCtick licensed technician to find the leak or restriction and fix it properly.
Reviewed by AC repair and service specialist on 22 October 2026. How we write our articles