Carrier
LED off
LockoutIGC dark
No 24V at the ignition control, or the module is dead.
Walk LED off in Diagnose
2 plates — walk the one on the cabinet
First check
1 Measure at the IFC under load
On Carrier 48FC line-voltage codes are incoming power. Measure L1/L2 (or L1/N) at the board while it is trying to run, not just at the disconnect. 24 VAC at IGC R to C. Control fuse / breaker on the unit board.
Expect: Voltage in the rating-plate window under load.
The rest of the walkthrough is Diagnose.
On the plates
- 24 VAC at IGC R to C. Control fuse / breaker on the unit board.
- W present during a heat call. Unoccupied shutdown will darken this LED.
- Door / heat-section plug seated. A rooftop heat-exchanger panel switch is easy to leave open.
Plates that use LED off
Same number, other makers
LED off on Carrier is not the same code on these plates.