They both should start spinning when you turn on the AC.

 

by 3 cent on this.. Happen to me last year. Both fans need to spin at the same rate of speed.. if one is spinning slower most likely the motor on the fan is going bad. Like others have said u may still have air in the system which can be fixed by refilling the system and make sure no air (bubbles) air in it. After u have done this run the car for awhile and watch the temp and see what happen.. Don't drive it just run it.. U want to get the car to normal operating temperatures. If the temp gauge starts going up and ya fans don't turn on it's the fan motor; since u had u have replaced the thermostat already.

 

Random fact, the FSM recommends filling slowly, something like 1L/minute or something. slowly filling will help reduce the amount of air to bleed out.

I used a lisle funnel, and bled on jackstand. I had to do three thermal cycles to get the air out enough for constant idle heat.

 

If the fans aren't coming on while running without the a/c on it means the thermostat hasn't opened yet. The coolant temperature sensor needs to see a certain degree of temperature before it will close the circuit and turning the fans on either low or high speed. The best thing to do is to hot soak the thermostat. Let the engine warm up with the rad cap off, once it starts to boil or your gauge reads 3/4(no more) put the cap on and shut off the car until it completely cools off i(deally over night). Check your level in the morning and top up as necessary. This might have to be done a couple of times. You don't want it to get too got, it's an aluminum block, once they overheat u run the risk of a new block.