On top of the fuse box

At this point , a scanner to test with , would be the most cost effective method to properly diagnose. IF you have already spent money on relays (assuming the correct ones) and a thermostat, AND ASSUMING that we are getting 'the whole story' , you may end up wasting a LOT of money on incorrect guesses! Could be any number of wiring/circuit issues , control issue or component issue. Most involved in the fan circuits can be easily tested and confirmed with the proper tool(s).