A Fault Detection Diagnostic (FDD) correction method for increasing the cooling capacity delivered by an Air-Conditioning (AC) system with an economizer comprising: correcting/superseding at least one cooling fault/delay, the correcting/superseding selected from the group consisting of: correcting/superseding a High-limit-Shut-off-Temperature (HST) fault/delay based on detecting an Outdoor Air Temperature (OAT) is less than or equal to a High-limit-Control Temperature (HCT) during a thermostat call for cooling to enable economizer cooling otherwise delayed by the at least one HST fault/delay, superseding a thermostat second-stage time/temperature-deadband delay based on detecting an OAT is greater than or equal to an AC Control Temperature (ACT) during a call for cooling and energizing an AC compressor otherwise delayed by a thermostat second-stage time/temperature-deadband delay, superseding at least one economizer second-stage time/temperature delay based on detecting a thermostat second-stage cooling signal and energizing an AC compressor otherwise delayed by the at least one economizer second-stage time/temperature delay.