On arrival found system off with low voltage short. Traced wire set and low voltage components to ensure no obvious damage to wiring or components. Isolated short to (R) circuit. Removed common and discovered short in AHU control board. Called and discussed findings with client, recommended replacement board along with installation of surge protection and enrollment in maintenance program. Client unable to approve any repairs beyond immediate failure. Estimate sent to client to approve, balance for repair to be collected on approval. We will need to coordinate with distributor tomorrow to confirm part availability and schedule repair.