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:

1. Make configuration change
2. Wait 30 seconds for auto-save
3. Power cycle to verify persistence
4. 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

1. Disconnect from MS/TP network
2. Connect dedicated power supply
3. Configure controller via direct connection
4. Power cycle and check if configuration persists

Step 3: Test Memory

1. Make a small configuration change
2. Power cycle immediately (within 5 seconds)
3. Check if change persisted
4. Repeat with 30-second wait before power cycle
5. Compare results

Step 4: Firmware Check

1. Note current firmware version
2. Check Carrier technical bulletins for known issues
3. If update available, follow Carrier procedure
4. 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