Upon arrival found downstairs system set to 72 and holding at 71. Also upon arrival found upstairs thermostat display showing that no common wire was detected. Pulled off face plate and properly secured common wire to port and display showed all connections were properly made. Provided a call for cooling and system started to function properly again. Unable to access indoor equipment to provide minor AC diagnostics due to door being locked. Supply temperature of upstairs equipment suggests that system functions properly again. System functions properly again at this time. Called homeowner to go over diagnostics and to explain that it’s a simple issue due to a loose wire. In attempt to provide diagnostics and explain that this call back isn’t due to anything our company has previously repaired on last visit the homeowner couldn’t contain her anger saying it’s what we repaired previously and that she didn’t want to pay. In further attempt to explain everything the homeowner cut me off mi