NO AC usually means the Pro-C display is surviving on backup power; a completely blank display can mean both normal power and battery display power are absent. Test the outlet first. With a working outlet, the useful next boundary is whether the transformer supplies roughly 24–28 VAC to the controller.
Match the pattern before opening anything
| Possible cause | Best clue | First check |
|---|---|---|
| Dead outlet or GFCI | Known-good device fails in the receptacle | Check switch, GFCI, and breaker |
| Failed transformer | Outlet works; AC terminals have no output | Measure 24–28 VAC secondary output |
| Loose facepack or connection | Display changes when panel is opened or reseated | Disconnect power and inspect connectors |
| Controller electronics fault | Correct low-voltage power reaches the unit | Document readings before replacement |
What this guide adds beyond the standard checklist
- First dividing test
- Separate NO AC from blank: Record whether the message is readable, the display is fully blank, or it resets. Those symptoms tell you whether backup power is involved.
- If the clue matches
- If you observe “Known-good device fails in the receptacle,” move dead outlet or gfci higher on the list and start with: Check switch, GFCI, and breaker.
- If it does not
- If that clue is absent, do not force the first diagnosis. Compare the system against “Outlet works; AC terminals have no output” and check: Measure 24–28 VAC secondary output.
Worked exampleYou installed a new battery and the Pro-C display returned, but it still says NO AC and no zones run. The result changes the next move: Test the outlet, then verify transformer output before replacing the facepack or controller.
Original conclusionThe battery restored the display only. It confirmed that normal transformer power is still missing. Test the outlet, then verify transformer output before replacing the facepack or controller.
Recognize the controller state
Original diagnostic reconstruction. Not a photograph of the product and not copied from a competitor.
Check these in order
- 01
Separate NO AC from blank
Record whether the message is readable, the display is fully blank, or it resets. Those symptoms tell you whether backup power is involved.
- 02
Test the outlet under load
Use a lamp or radio at the same receptacle. If it fails, do not open the Pro-C; the problem is upstream in the household circuit.
- 03
Remove the backup battery as a clue
If a readable NO AC display goes blank after the battery is disconnected, the display had been running on battery. This supports a missing transformer supply.
- 04
Measure the transformer boundary
Hunter specifies about 24–28 VAC at the transformer or controller AC terminals. High-voltage primary testing and hardwired controllers belong to a qualified electrician.
- 05
Power-cycle only after supply is proven
If correct low-voltage power reaches the controller, cycle power once and inspect accessible panel connections. Persistent blank or NO AC behavior then points beyond the transformer.
- The controller is hardwired.
- The transformer primary side requires testing.
- Correct 24–28 VAC reaches a controller with a blank or unstable display.
What homeowners ask about this symptom
Can a bad battery cause NO AC?
The battery is not the normal AC source. A bad battery may make the display unavailable during an outage, but replacing it does not restore transformer power.
What transformer voltage should a Pro-C have?
Hunter's troubleshooting guidance identifies approximately 24–28 VAC on the secondary side.
Sources and review notes
General maintenance logic is checked against EPA WaterSense outdoor irrigation guidance. Product controls and disassembly steps vary by model; use the current manufacturer manual for your exact valve, controller, or sprinkler head.
Published and last reviewed: August 29, 2026