GSHA Services, LTD performed a thermostat and cooling system diagnostic at a home on East Prairie Road in Evanston, IL. The homeowner's Google Nest thermostat was calling for cooling but the air conditioner was not responding reliably. Our HVAC technician checked the thermostat wiring and common-wire power at the furnace control board, tested the low-voltage circuit and safety switches, then inspected the outdoor condensing unit, contactor, capacitor and refrigerant lines. We corrected the control wiring, cleaned the condenser coil, verified refrigerant pressures and confirmed the Nest was controlling the system correctly with a proper temperature split at the registers. Smart thermostat compatibility problems are a common cause of intermittent cooling, and a proper diagnostic avoids replacing parts that are not broken. GSHA Services provides air conditioning repair, smart thermostat installation, HVAC maintenance, furnace repair and full system replacement in Evanston, Skokie, Wilmette, Morton Grove, Lincolnwood, Chicago and throughout Cook County, Illinois.