What Does Error Code 79 Indicate?
Trane RTU Error Code 79 commonly indicates a communication fault between the unit controller and a connected module or sensor.
The unit may:
- Enter fault mode
- Display intermittent operation
- Show module offline alarms
Common Causes
- Loose communication wiring
- Damaged control harness
- Module failure
- Address conflict
- Control board malfunction
- Grounding issues
Troubleshooting Steps
1. Inspect Communication Wiring
Check:
- RS-485 polarity
- Shield grounding
- Loose terminals
2. Verify Addressing
Ensure unique module addresses.
3. Power Cycle Modules
Shut down and restore power to clear transient faults.
4. Replace Faulted Module (If Confirmed)
Only after wiring and addressing are verified.
FAQ
Does this require replacing the RTU?
No. Most cases involve wiring or module issues.
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