The fan and the compressor of my a/c do not work, it seems that the electric board is getting 24V in but it is not coming out to the contactor relay.

If 24v is going in, but not coming out,, its time to replace,, are you sure you don`t have 24 volts at the contactor,, usually the 2 smallest wires that plug into the lower sides of the contactor,, be careful electricity bites hard and deep

It will help if you can tell us the brand and model of the system. A lot of the newer systems will have time delays,high pressure switches,low pressure switches and thermal overloads. All of the previous can keep the contactor from getting 24 volts and closing.