4828-0100594 -

: Check the onboard fuse (usually a small glass or ceramic cylinder). If blown, investigate the 24V transformer or external shorts before replacing the board.

: Disconnect all power sources to the HVAC unit. Large industrial systems may have multiple power feeds; verify with a voltmeter. 4828-0100594

: Take high-resolution photos of all wiring connections before disconnecting the old board. Label individual wires if they are not already color-coded or tagged. : Check the onboard fuse (usually a small