What Does Alarm 78 Indicate?
Carrier ComfortLink Alarm 78 generally indicates a communication failure between the main controller and a module or sensor.
Affected modules may appear offline.
Common Causes
- Broken communication wiring
- Loose terminal connections
- Incorrect addressing
- Failed communication module
- Electrical interference
- Grounding issues
Troubleshooting Steps
1. Inspect Communication Bus
Check polarity, continuity, and termination.
2. Verify Addressing
Ensure no duplicate device addresses.
3. Power Cycle Modules
Clear temporary faults.
4. Replace Faulted Module if Necessary
Only after verifying wiring and addressing.
FAQ
Is this the same as a sensor fault?
No. It specifically refers to communication failure.