Run the air con self test - see below courtesy of SD1TOO -see what error code you get.
You can perform a manual diagnostic check of the system by pressing and holding the AUTO switch and the air distribution switch, then turning the ignition switch from 0 to II. The audible warning and all the indications on the control panel display cycle on and off whilst the ATC ECU runs the diagnostic check.
When complete, all the indications in the display are replaced by FC in the left-hand temperature window and two digit fault codes in the the right-hand window which cycle in numerical order. An audible warning sounds as each fault code is shown.
The check is cancelled by pressing the OFF switch or turning the ignition switch to 0. If there are no faults, the system reverts to normal operation. In low light conditions the sunlight sensor (top centre of dash) should be illuminated with a strong light source.