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 |
Read the system before replacing a part
Use the observation that most closely matches your yard. Each row changes the next test, so you do not spend an afternoon proving the wrong theory.
What it meansBackup battery power is preserving the interface.
Do nextTest the receptacle before assuming the Pro-C facepack failed.
What it meansAC supply, transformer, connection, fuse on applicable older models, or controller electronics may be involved.
Do nextIdentify the exact Pro-C generation before following a parts diagram.
What it meansThe transformer or its input connection is the boundary.
Do nextUse a qualified person for hardwired primary-side work.
What it meansThe controller-side power path or facepack is suspect.
Do nextDocument model, generation, and readings for Hunter support.
Four tests that narrow the fault
Stop as soon as one result gives you a clear boundary. The goal is not to perform every test; it is to eliminate whole groups of causes safely.
- 01
Identify message and generation
Photograph the display and Pro-C model label before opening any compartment.
IF YES / NORMALThe correct generation-specific power diagram can be used.
IF NO / ABNORMALDo not assume old and new Pro-C parts or layouts match.
- 02
Load-test the power source
For plug-in models, test the same outlet with a working device; hardwired models require an electrician.
IF YES / NORMALThe external source is available.
IF NO / ABNORMALRepair the building-power issue first.
- 03
Check accessible low-voltage connections
Remove power and inspect only documented secondary connections for looseness, heat, or water.
IF YES / NORMALConnections are secure and dry.
IF NO / ABNORMALDamaged wiring or water intrusion requires service.
- 04
Compare transformer output
A trained person measures the secondary and compares it with Hunter's approximately 24–28 VAC guidance.
IF YES / NORMALCorrect input at a dead controller points internally.
IF NO / ABNORMALMissing secondary output points upstream.
Numbers worth measuring
Measure only at documented low-voltage points; exact model instructions control.
Common fixes that waste time
A new interface cannot operate without its correct low-voltage supply.
Layouts, components, and service steps changed; use the exact label and manual.
A reset cannot create missing AC power.
How the evidence changes the repair
An older Pro-C had a blank display after a storm.
- The plug-in receptacle powered a lamp normally.
- No specified secondary voltage reached the controller.
- A correct replacement transformer restored a stable display and retained programming.
The live outlet ruled out the building circuit, while the missing secondary isolated the transformer. The facepack was never the failed part.
How to confirm the repair actually held
A single successful start can hide an intermittent splice, sticky valve, remaining leak, or scheduling problem. Recreate the original conditions before calling the job finished.
Pass: The original symptom does not return during the direct test.
If not: Stop and repeat the last dividing test; the fault boundary was incomplete or intermittent.
Pass: Automatic behavior now matches the documented controller state.
If not: Hardware may be repaired while schedule, sensor, program, or connectivity logic remains separate.
Pass: The repair holds under normal time, load, moisture, and network conditions.
If not: Use the first changed condition to identify the remaining intermittent cause.
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 30, 2026