It may or not be normal for the fans to come on with the A/C. As I described, the fans will come on low speed IF the freon pressure is high enough. This of course is with the A/C switched on. Usually the fans will cycle on and off, as the fans help reduce the high pressure just as they reduce the coolant temp. If the A/C system works well, I would ignore them coming on with the A/C on, at least this establishes that the fans do in fact operate. The second stage, high speed fan will come on only when the engine temp reaches either 100 or 105 degrees celcius. If the low speed fan is already running due to the A/C , the high speed fan will take over.
I would try getting it up to an overheated state, over 100+ to see if the fans come on high speed. Well, first I'd try finding the temp sensor as I suggested just to see if they come on high speed if you pull the connector, just to test the system itself, then run it up to a high temp to see if the fan comes on high speed. If the system is capable of working by pulling the connector, but doesn't come on at high engine temp, then I'd try the temp sensor itself.
If the fans are working OK, coming on at high engine temp, but the overheating concern is still there, then I'd look at the radiator concern I mentioned before.
One final observation is that you said the engine fan clutch(on the front of the engine itself) was replaced, just be sure they didn't put the blade on the clutch backwards, it'll be easy to tell if the fan is blowing back towards the engine with the engine running, or if some dufus has it backwards and it's blowing forward towards the radiator. Seen this happen at a body shop once.