Cooling fan relay

My engine cooling fans wont run. I have repaced the relay for the fans but that didn't do the trick. They run when I check the trouble codes so I know that they are in good working order. Is there a curcuit that I am missing or could the temp sensor be faulty? Please Help!

Temp sensor could be faulty even the PCM could do it! Start your car up and turn on the air conditioning or the defrosters and see if the fans come on then!

I checked to see if they would come on with it running and with the AC on and nothing happened. The fans only come on when I put my code reader in to check the trouble codes.