Arrived in Elgin for AC Maintenance, Upon our arrival we spoke with the customer about their concerns with the HVAC system not cooling. Performing our diagnostics we found that the system had a communication fault between the indoor and outdoor units. We inspected both portions of the system and did not find anything wrong with the voltages coming in or the communication wires. We reset the system and put it into test mode. After running the system for 30 minutes we found no issues with the system at this time. Moving forward the son is going to monitor this and inform us if this happens again.