Carrier 19XL - Manual (Page 231)

Red Led
If the LED is blinking continuously at a 2-second rate, it is indicating proper operation. If it is
lit continuously it indicates a problem requiring replacement of the module. Off continuously
indicates that the power should be checked. If the red LED blinks 3 times per second, a
software error has been discovered and the module must be replaced. If there is no input
power, check fuses and the circuit breaker. If fuse is good, check for shorted secondary of
transformer, or if power is present to the module, replace the module.
Green LEDs
There are one or 2 green LEDs on each type of module. These LEDs indicate
communication status between different parts of the controller and the network modules as
follows:
LID Module
Upper LED — Communication with CCN network, if present; blinks when communication
occurs.
Lower LED — Communication with PSIO module; must blink every 5 to 8 seconds when the
LID default screen is displayed.