Upon arrival system was operational, refrigeration is within range no safety issues or trips. Monitored condenser defrost control board found odd LED blink not code but more links to internal short, tap to control board found contactor disengage momentarily. Suspect intermittent defrost control board failure recommend replacement of defrost control board client has agreed defrost control board paid in full. Due to age of unit client would like to get pricing for a new system replacement appointment set up tomorrow 2 to 4 with Corey. Unit is operational at this time.