The most common ATS controller failure signs are a blank or frozen display, a transfer that fails or stalls during a test, source readings that don't match what's actually on the line, and recurring communication or memory errors. Several of these can also come from wiring, settings, or the switch mechanism. So treat them as reasons for a qualified electrician to investigate, not as proof the controller is bad.
The automatic transfer switch (ATS) controller is the switch's decision-maker. It monitors both power sources, runs the programmed time delays, starts the generator, and signals the switch mechanism to transfer and retransfer. Examples here use Eaton's ATC-300+, the transfer switch controller on Eaton's LMR Plus FT-series fire pump controllers, along with its published troubleshooting guidance.
ATS controller symptom checklistIf you see any of these, record the display message and when it happened, then call a qualified electrician.
- Display blank, frozen, or all status LEDs off
- Unit Status LED not blinking in normal operation
- Front-panel pushbuttons not responding
- Generator doesn't start, or the load doesn't transfer, during a test
- A source shows as unavailable when it's actually good, or one or more phase voltages read wrong
- Switch position not shown as connected when it should be
- Memory errors, such as setpoints or options errors
- Lost communication with remote monitoring
Is the Problem the Controller, the Switch, or the Settings?
Answer this first, because the fix is different for each. A controller problem means the logic unit itself isn't sensing, deciding, or commanding correctly. A switch mechanism problem means the controller issues a command but the main contacts don't move or don't report their position. A settings or input problem means the controller is doing exactly what it's been told.
Eaton's ATC-300+ manual makes the distinction concrete. If a source device fails to open or close within its allotted time, the controller alarms and shows a Source 1 or Source 2 device error. That's a sign to check the switch and its auxiliary contacts, not necessarily the controller. Messages such as Lockout, ATS Not in Automatic (Monitor Mode), and Emergency Inhibit mean a control input is holding the controller back on purpose. They aren't failures.
Transfer switch enclosures contain hazardous voltages from more than one source. Eaton's manual limits problem-solving to qualified personnel using lockout procedures. Leave testing and any work inside the enclosure to a qualified electrician following the manufacturer's documentation.
What Does a Blank or Frozen Display Mean?
A dark display, LEDs that are all off, or buttons that don't respond are the most visible failure signs. They don't always mean a dead controller.
In Eaton's troubleshooting guide for the ATC-300+, the first probable cause for all LEDs being off is missing or deficient control power. A controller malfunction is second. The ATC-300+ runs on 65–145 Vac control power, so the upstream supply is checked first. Unresponsive pushbuttons, on the other hand, are listed as an internal connection problem with replacement as the solution.
The Unit Status LED is a useful health check. On the ATC-300+, it blinks about once per second in normal operation, which shows the controller has passed its self-diagnostic checks of the microprocessor and memory. If it isn't blinking, Eaton lists control power, a switch stuck waiting for the neutral position, or a controller malfunction as possible causes.
Why Would a Transfer Switch Fail or Delay a Transfer During a Test?
A failed or slow transfer during a test is a serious sign. Before blaming the controller, though, rule out the programmed time delays and the generator.
- Programmed delays: transfer and retransfer are deliberately timed. On the ATC-300+, delays such as time delay normal to emergency and time delay emergency to normal can each be set up to 1,800 seconds. A "slow" transfer may simply be a delay doing its job.
- Generator start: if the engine doesn't start after the engine-start delay, Eaton lists the generator start contacts not closing, or wiring at the generator, as probable causes.
- Generator never becomes available: during an engine test, the ATC-300+ waits a set time for the generator source to come up. If it doesn't, the controller aborts the test and alarms. That usually points to the generator, not the controller.
- Switch doesn't move: a Source 1 or Source 2 device error points to the transfer mechanism or its position contacts.
If the delays are set correctly, the generator is available, and the switch mechanism checks out, yet the controller still won't command a transfer, that's when the controller becomes the likely cause.
What Does Erratic Source Sensing Look Like?
Erratic sensing shows up as a controller that declares a good source unavailable, transfers when nothing is wrong with utility power, or displays phase voltages that don't match independent measurements.
Eaton's guide lists two common causes for a source showing as unavailable when it shouldn't: voltage or frequency actually outside the setpoints, or setpoints that don't match the system. One detail matters on the ATC-300+. Changing the nominal voltage or frequency setpoint automatically resets the pickup and dropout settings to new defaults, which can make the controller appear to misbehave after a settings change. When one or more phases read incorrectly, Eaton points to wiring first, then the controller.
In a fire pump installation, source settings are part of the system's commissioning. Changes should go through the qualified personnel responsible for the system and the authority having jurisdiction.
What Do Communication and Memory Errors Mean?
Some messages point straight at the controller's internal electronics. On the ATC-300+, a Setpoints Error or Options Error indicates a memory problem, and Eaton's instruction is to contact the factory.
Communication problems are different. The ATC-300+ reports to remote systems over RS-485 with Modbus. If a building monitoring system or remote annunciator loses contact, the cause can be the communication wiring, the Modbus address or baud rate settings, or the controller's port. A qualified technician should work through those before condemning the controller.
Should You Repair or Replace an ATS Controller?
For the ATC-300+, Eaton's answer is replace. Its manual states that if a malfunction is traced to the controller, the unit should be returned to Eaton for a replacement. The circuit boards are calibrated and conformally coated at the factory and are to be serviced only by factory-trained personnel.
There's also a matching step. Eaton factory-programs each ATC-300+ for a specific transfer switch and advises against interchanging controllers without consulting Eaton. A replacement has to be confirmed against your switch, and all setpoints should be verified after installation.
On Eaton's newer EPCT Fire FT controllers, the transfer switch functions are built into the controller's touchscreen. Diagnosis follows that controller's own manual.
What Information Should You Gather Before Ordering a Replacement?
Collect this before you call, and the replacement can be matched to your switch in one conversation:
- Transfer switch catalog number, plus its General Order number (GO#) and item number, from the switch nameplate.
- Controller model and style number, for example ATC-300+, from the controller.
- Firmware version and options. On a working ATC-300+, pressing Help/Lamp Test from the home screen scrolls these across the display. On a dead unit, use the label on the back of the controller.
- System voltage, phase, and frequency.
- For fire pump installations, the fire pump controller model and serial number, such as an FT-series unit.
- The display messages you recorded and when they occurred.
For LMR Plus FT-series fire pump controllers, see the ATC-300+ automatic transfer switch controller, and confirm the match before ordering.
ATS Controller Failure FAQs
What are the signs of a bad transfer switch controller?
Common signs include a blank or frozen display, status LEDs that are all off, unresponsive buttons, a failure to start the generator or transfer the load during a test, sources reported as unavailable when they're good, incorrect phase voltage readings, and memory errors. Many of these can also come from control power, wiring, settings, or the switch mechanism, so have a qualified electrician confirm the cause.
How can you tell if the ATS controller or the switch mechanism has failed?
Watch what happens after the controller commands a transfer. If the controller signals correctly but the main contacts don't move or don't report their position, the problem is likely in the switch mechanism or its auxiliary contacts. Eaton's ATC-300+ reports this as a source device error. If the controller never commands the transfer when it should, the controller is the likely suspect.
Can an ATS controller be repaired?
For Eaton's ATC-300+, the manufacturer's guidance is replacement, not field repair. Eaton states a malfunctioning controller should be returned for a replacement, and that its circuit boards are factory-calibrated and serviced only by factory-trained personnel. The replacement must also be matched to your specific transfer switch, because Eaton factory-programs each unit for a specific switch.
Why does my transfer switch take so long to transfer?
Often it's by design. Transfer switch controllers apply programmed time delays before starting the generator, before transferring to the alternate source, and before retransferring to normal power. On Eaton's ATC-300+, some of these delays can be set as long as 1,800 seconds. If the delays are set correctly and the transfer still doesn't happen, a qualified electrician should investigate.
What does "Lockout" mean on an ATC-300+ display?
Lockout means the controller has detected that one of the switch's breakers has tripped, and it's blocking further automatic transfers. It's a protective state, not a controller failure. Per Eaton's manual, once the fault is cleared, the alarm is reset at the controller to restore automatic operation. A qualified electrician should find and correct the cause of the trip first.
Find a Replacement ATS Controller
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For help matching a replacement controller to your switch, call (786) 336-5783 with your switch catalog number, controller model, and system voltage, or send them through our contact form. Eaton's ATC-300+ instruction booklet has the full troubleshooting guide for qualified personnel.