Gday mate,geoff here, what i have found in the past is that as most vehcles have the heater on all the time and the temperature from it is controled via a air flap the opens and closes, check list, is there leaves , what-not trapping the flap, vents, are the vacuum hoses contecting the systems under the dash connected and operating, is the A/C actually coming on ? is there an A/C fault under the hood? hope this starts the procss fro you,geoff.