[DFBonnett]

What MW said is, of course, the correct procedure.
However, for a possible quick and dirty fix you might first try unplugging then reconnecting the sensors along the AC lines. A dirty connection can give you a bogus code. BTDT.
Second, clear the codes through the comp using the DIC or disconnecting the battery for a minute. With the engine off, hook up the AC recharge kit and open the valve. Start the car. It should pull enough out of the can so that the compressor stays running to accept the charge. BTDT too.
FWIW
YMMV