Air con fault

hey guys, i have had the "book" symbol come up on my air con unit, i have searched the forums and can only find threads saying "take it to a specialist". Is there a way i can diagnose the fault without having to fork out specialist money? (it may be something as simple as a re-gas)

Thanks

Very common fault on the P38 aircon is the Condenser (Radiator thingy behind the grille with the two fans on) leaking-usually at the top l.h. corner. Before filling it with expensive 134a gas, take it to an aircon specialist and get the system filled with nitrogen and if there is a serious leak you will hear it as the gas goes in, otherwise, leave it in for a few days and see if the pressure has held-then get it gassed up. The compressor will not run unless there is a certain minimum pressure in the system to start with. The Book symbol can signal lack of refrigerant. Question if it's empty is where has it gone from???

ok, thanks for that, il give that a go

just had this prob..(this week) took it to Independant LR dealer he hooked it up showed HEARTER CORE SENSOR.. charged me £47 to hook it up and £11 for the sensor.. work fine now and no book symbol...