Carrier SystemVU Configuration Loss After Power Cycle
This article addresses the common issue of Carrier SystemVU controllers losing their configuration after power loss.
Symptoms
- BACnet device instance and MAC address reset to defaults after power cycle
- Zone sensor vs thermostat configuration reverts
- Custom setpoints lost
- Schedule assignments cleared
- Problem occurs whether or not MS/TP is connected
Root Causes
1. EEPROM/Flash Memory Failure
The most common cause. SystemVU controllers store configuration in non-volatile memory that can fail over time.
Indicators:
- Consistent loss after every power cycle
- No pattern to which settings are lost
- Controller is 5+ years old
Solution: Replace the controller. EEPROM failures are not field-repairable.
2. Firmware Bug
Some SystemVU firmware versions have known bugs related to configuration persistence.
Indicators:
- Multiple controllers with same firmware version affected
- Problem started after firmware update
- Specific settings lost consistently
Solution: Check for firmware updates from Carrier. Document the current version before updating.
3. Incomplete Configuration Save
Configuration changes may not be properly committed to non-volatile memory.
Indicators:
- Recent changes lost, but older configuration retained
- Problem only after making specific changes
Solution: After making changes, perform explicit save/commit operation:
- Make configuration change
- Wait 30 seconds for auto-save
- Power cycle to verify persistence
- If lost, try using Carrier configuration tool to force save
4. Power Supply Issues
Insufficient or unstable power can prevent proper save operations.
Indicators:
- Configuration lost during brownouts, not clean power cycles
- Other controllers on same power circuit unaffected
- Controller exhibits erratic behavior before losing config
Solution:
- Verify 24VAC supply voltage (should be 24V +/- 10%)
- Check VA rating of transformer vs total load
- Add dedicated transformer for problematic controller
5. Communication Conflicts
In rare cases, constant communication attempts during shutdown can corrupt configuration.
Indicators:
- Problem only when connected to MS/TP network
- Works fine standalone
Solution:
- Check for MS/TP bus issues (termination, wiring)
- Verify no MAC address conflicts
- Try isolating controller from network during testing
Diagnostic Steps
Step 1: Document Current State
Before troubleshooting, record:
- Firmware version
- Device instance and MAC address
- All non-default configuration settings
- Power supply specifications
Step 2: Isolate the Controller
- Disconnect from MS/TP network
- Connect dedicated power supply
- Configure controller via direct connection
- Power cycle and check if configuration persists
Step 3: Test Memory
- Make a small configuration change
- Power cycle immediately (within 5 seconds)
- Check if change persisted
- Repeat with 30-second wait before power cycle
- Compare results
Step 4: Firmware Check
- Note current firmware version
- Check Carrier technical bulletins for known issues
- If update available, follow Carrier procedure
- Test configuration persistence after update
Workarounds
If Controller Must Stay in Service
Option 1: UPS Protection
- Add small UPS to controller power circuit
- Provides time for proper shutdown
- Note: This masks the problem, doesn't fix it
Option 2: Network Re-push
- Store configuration in supervisory controller
- On communication restore, automatically push settings
- Requires programming in the supervisory system
Option 3: Scheduled Configuration Backup
- Use BACnet write commands to refresh critical settings periodically
- Ensures settings are re-established if lost
- Can be automated from Niagara or other supervisory
Replacement Considerations
When the controller needs replacement:
| Factor | Consideration |
|---|
| Warranty | Check if still under Carrier warranty |
| Availability | SystemVU may be discontinued - check part availability |
| Compatibility | Ensure replacement works with existing sensors/actuators |
| Migration | Consider upgrading to newer Carrier platform |
Prevention
For new installations:
- Use quality power supplies with adequate VA rating
- Install surge protection on 24VAC circuits
- Keep firmware updated
- Document all configurations externally
- Test configuration persistence during commissioning