I have problem with the AC compressor in my 2004 kia carnival which was working fine until i swaped the engine in the local workshop. I checked all fuses they are seems to be good. I tried to wire the compressor directly to the car’s battery and the clutch engaged. What do you think the problem is?
Do you have refrigerant in the system? It may have leaked out if a pipe was nudged during the engine change. If refrigerant is low, the AC compressor will never be given the Turn On signal from the ECU.
The fact that the compressor runs when you give it power directly indicates that you're not suffering from compressor clutch wear.
Most of the time clutch wears off and engage only when the car is cold, once everything heats up clutch stops engaging. You can readjust the clutch plate and make it work again, but this is only temporal fix.
I don't know if you ever figure it out but I had the same problem and the dealer said the fuse box needs to be changed for me. I had enough freon and the pressure switch was working just fine.