Truck Repair: A/C fan wont kick on, dd series, wont kick

Question
I have 04 Freightliner Columbia with a DD series 60.I replaced all bunch of parts but the fan still wont kick on and its building a pressure 400.New lo and HI switches, new fan solenoid, new expansion valve. ac drier, and new ac compressor installed 3 months ago.

Answer
If your high side line is building to 400 psi you have something blocked somewhere. high side pressure should be around 275 psi. Other thing is with all your switches turned on and the truck running have you made sure that you have power at the compressor plug.