Symptoms: - there are two fans: radiator and A/C - when A/C off, radiator fan does not turn on automatically - when A/C is turned on, both fans turn on and off at the same time automatically - engine temperature gauge shows close to overheating (assumed to be correct as temperature gauge appears working when car is warming up) - turning on A/C appears to bring down the temperature shown on the temperature gauge Troubleshooting Steps Performed: - radiator coolant was flushed and refilled - checked relay fuses to radiator and A/C fan - unplugged the temperature gauge connector (next to coolant temperature sensor) in engine bay. Gauge on dashboard unresponsive. - unplugged the coolant temperature sensor in engine bay. "Check Engine" light on dashboard comes on. - warmed up the car to normal temperature with radiator cap off to see if radiator fluid was circulating. Inconclusive due to car shakiness. - gauged temperature of top and bottom radiator hoses by hand. Both seemed to be equally hot, although, turning on A/C seemed to make bottom hose slightly cooler Possibly Relevant Info: Car is a 1994 Toyota Camry 4-cyl. Question: Which could it be: thermostat, coolant temperature sensor, or other? EDIT: Added more troubleshooting steps performed.