An Actron Air E51 fault code means the indoor and outdoor units of your system have stopped talking to each other. The usual causes are a damaged or loose communication cable, a power supply problem at the outdoor unit, or a faulty or incorrectly configured control board. A full power reset is the only fix a homeowner should try; if E51 comes back, the system needs a licensed technician.
E51 tends to show up at the worst moment, usually when the system has been working hard through a hot spell or has just come back on after a storm. The good news is that it is a communication fault rather than a refrigerant or compressor failure, so it is often a repair rather than a replacement. This guide covers what E51 means, what you can safely check yourself, and what a technician does to fix it, so you know what you are dealing with before you book a service call.
What Does The Actron Air E51 Fault Code Mean?
E51 is ActronAir’s code for a communication error between the indoor unit and the outdoor unit. The two units exchange data constantly through a dedicated communication cable. When the indoor board stops receiving valid signals from the outdoor board, the system shuts down and displays E51 rather than running blind.
ActronAir’s own E51 guidance for the LR7 wall controller says the code is “typically associated with loss of communication”. The LR7 is used with the Classic, ESP Plus, ESP Ultima and Advance split ducted ranges. ActronAir’s product fault code list assigns the same indoor-to-outdoor communication meaning to E51 across several product families:
- Advance split ducted (CRV/EVV)
- Aires split ducted (CRS/EVA)
- Ultra Slim split ducted, including the R-32 models
- Cascade wall-hung split systems, including the R-32 models
- Multi-split systems (MRE/BRE)
- Variable commercial split and package systems
So whether you have an Actron ducted system in the ceiling or a Cascade split on the wall, E51 points to the same basic problem: the link between the two halves of the system has broken down.
How Is E51 Different From E50, E52 And E6?
E51 sits in a group of Actron communication and configuration codes that are easy to mix up. The code number tells a technician which link in the system has failed, and that decides where they start looking.
| Code | What ActronAir lists it as | Where the fault sits |
| E50 | Configuration error (outdoor board) | Outdoor board settings |
| E51 | Indoor / outdoor unit communication error | Cable and boards between indoor and outdoor units |
| E52 | Communication error between indoor unit and wall controller | Controller cable, wall controller or indoor board |
| E6 | Communication problem within the system | Indoor unit, outdoor unit or wall controller |
If your screen shows E6 rather than E51, our guide to the Actron Air E6 fault code covers that one in detail. For the wider list, see Actron Air fault codes explained.
What Causes An Actron Air E51 Fault Code?
Four things cause almost every E51 fault. ActronAir’s troubleshooting guide for the Advance and Aires ranges points to the communication cable, the indoor and outdoor boards, the outdoor board configuration, and the power supply to the units.
- A damaged or loose communication cable. The cable runs between the indoor and outdoor units, often through the roof space and along an external wall. Loose terminals, corrosion at the connections, rodent damage or a cable nicked during other work will all break the signal.
- Power supply problems at the outdoor unit. If the outdoor unit has lost power, or the supply voltage is too low, it cannot talk to the indoor unit. ActronAir’s troubleshooting guide specifies more than 187 volts AC for the drive to operate.
- A faulty indoor or outdoor control board. Power surges, storms and age can damage the circuit boards that handle communication. A board fault usually brings E51 back straight after a reset.
- An incorrectly configured outdoor board. ActronAir lists configuration as a cause, which matters most after a new install or a replacement board. A board that has not been set up to match the system will not communicate properly.
What Can You Safely Check Yourself?
A full power reset is the one fix worth trying before you book a technician. It clears a temporary communication glitch, which is common after a blackout or a storm, without anyone opening a panel.
- Turn the system off at the wall controller.
- Switch off the air conditioning circuit breaker at your switchboard, and the isolator switch next to the outdoor unit if you have one.
- Leave the system off for a few minutes.
- Switch the power back on at the switchboard and the isolator, then restart from the controller.
- Give the system time to start up fully before judging whether E51 has cleared.
While you are at the outdoor unit, check two things by eye only. Make sure the isolator switch has not been left in the off position after a service or garden work. Then look for obvious damage to the cabling where it enters the unit, such as chewed insulation or a cable pulled loose. Do not open the unit or touch the wiring.
If the circuit breaker trips again when you switch it back on, leave it off. That is an electrical fault, and it needs a technician rather than another reset.
When Does An E51 Code Need A Technician?
Call a technician when E51 returns after a full power reset, when the circuit breaker keeps tripping, or when you can see damage to the cable. ActronAir’s fault code documentation also advises turning the unit off and contacting a technician if the problem persists after the basic checks.
Everything past a power reset involves live electrical work. Testing the communication cable, checking terminals, measuring supply voltage and reconfiguring a control board all mean opening the units while they are connected to mains power.
In New South Wales this is licensed work. The NSW Government’s air conditioning and refrigeration licensing guidance states that you need a licence or certificate before doing air conditioning and refrigeration work in the state. That licence covers the associated electrical wiring work, including diagnosing control circuits and repairing cable terminations, which is exactly what an E51 repair involves.
How Does A Technician Fix An Actron Air E51 Fault?
A technician works through the communication link in order, from the simplest cause to the most expensive. That order matters, because it stops a cable fault from being misdiagnosed as a failed board.
- Check the power supply to both units, including voltage at the outdoor unit.
- Inspect the communication cable end to end, including terminals, polarity and connections at both boards.
- Test the indoor and outdoor boards to find which one has stopped communicating.
- Check the outdoor board configuration against the system, and reconfigure it where needed.
- Repair or replace the faulty cable or board, then run the system to confirm E51 has cleared.
All General Air is an ActronAir authorised service agent, so Actron systems are our core work rather than one brand among many. If your system is still under warranty, tell us when you book, as that affects how the repair is handled. You can find out more about our Actron Air servicing and maintenance for ducted and split systems.
What Does An E51 Repair Usually Involve?
Most E51 repairs fall into one of three levels of work. The fix a technician lands on depends on which step of the diagnosis finds the fault.
| Cause found | Typical fix | Scale of the job |
| Tripped breaker, isolator off, temporary glitch | Power reset and system check | Minor |
| Loose, corroded or damaged communication cable | Re-terminate or replace the cable run | Moderate, depends on access to the roof space |
| Faulty or unconfigured control board | Reconfigure or replace the board | Larger, depends on parts |
A proper diagnosis is also what separates a board replacement from a whole new system. Several of our Google reviewers came to us after being told their Actron system needed replacing, and found the fault was a single part. If you are weighing up repair against replacement for an older unit, our ducted air conditioning team can talk you through both options.
Frequently Asked Questions
Can I keep using my Actron air conditioner with an E51 code? No. The system shuts down when E51 appears because the indoor and outdoor units cannot coordinate. Try one full power reset. If the code returns, leave the system off until a technician has checked it.
Will a power outage cause an E51 fault code? Yes, it can. A blackout, brownout or storm can interrupt communication between the units, and a full power reset often clears it. If a power surge has damaged a control board, E51 will return after the reset.
Does E51 mean my Actron system needs replacing? Usually not. E51 is a communication fault, and the most common causes are a cable, a connection, a power supply issue or a single control board. Replacement only makes sense if the system has other major faults or is near the end of its working life.
Can I replace the Actron communication cable myself? No. In NSW, air conditioning work, including the associated electrical wiring, needs a licensed technician. Replacing or re-terminating a communication cable means working inside units connected to mains power.
Does E51 show up on Actron split systems as well as ducted systems? Yes. ActronAir lists E51 as an indoor-to-outdoor communication error for Cascade wall-hung split systems and multi-split systems, as well as the Advance, Aires and Ultra Slim ducted ranges. Our split system air conditioning page covers the split range.
When Is It Worth Calling A Technician About An Actron E51 Code?
Call as soon as E51 comes back after a full power reset, or straight away if the breaker keeps tripping. The fault will not clear on its own, and a proper diagnosis stops a cable problem turning into an unnecessary board or system replacement.
All General Air is an ActronAir authorised service agent based in Wetherill Park, servicing Actron systems across the Eastern Suburbs, Inner West, Northern Beaches, North Shore, St George, Sutherland Shire and Western Sydney. We hold a 4.5-star Google rating from 97 reviews.
Seeing E51 on your Actron controller? Contact All General Air or call us on 02 8788 8600 to book a service. Tell us your system model and when the code first appeared, and we’ll be in touch within two hours.