I have a 1999 Camry CE - 4 Cylinder. Wondering whether the dual fans are both supposed to run simultaneously always - when the engine is hot??

General strategy is that there is a temp sensor screwed into the head, touching the coolant. when the coolant attains a preset temp, the sensor turns on a relay which puts power to the fans. also when you turn on the A/C, this goes around the sensor circuit and runs the fans as long as the A/C is on. so if your fans are not running period, first disconnect them and jumper them directly to the battery. if they run then they are good and you look next to the relay, if they do not run on battery then go buy a new fan set at a parts store. the relay is generally in a box with other relays and they are all the same so you swap the fan relay with another and if the fans run you have identified a bad relay. go to a parts store and buy another. if the fans still do not run you have to look to replacing the sensor, this little guy resembles a chess piece with a wire connector at the top, and it is about 10 bucks. it screws into the engine with plumbing threads so do not go medieval when you are screwing in the new one, snug plus 1/4 turn. have the new one ready to go when you take the old one out as coolant will be slowly draining out.

good luck