Fault Code Lookup

HVAC Sales Master
Red LED on by itself (fuse good)
Entire control should be replaced
This code typically points to
  • Internal board failure

Next checks to confirm
  1. Verify fuse is good
  2. Verify proper power and ground
  3. Replace board if confirmed

Escalation
Already a board-level escalation once supply and fuse are ruled out. Control is not field-repairable.
Reset behavior
Not a normal auto-reset fault.
Urgent
Fix now
Source
Emerson 50V64-743 diagnostic features