Strange aircon fault

[solophoto]

Can anyone shed any light on this? My aircon works perfectly - UNLESS the temperature in the car is above around 30-32 degrees, eg on a hot day left in the sun with windows closed. It resolutely refuses to work until we have been driving along for half an hour or so with the windows open, and then will suddenly kick in and cool the car perfectly. On a colder day it will immediately come on and work perfectly. How strange is this?

Any answers?

Thanks,

Burl

[mikeWalsall]

Sunlight sensor (top right of dashboard) covered ..??

Cabin thermostat (small grill at left of radio) needs de dusting ..??

[Simon Jones]

May be a sign that it needs a re-gas. If the pressure is low, the compressor won't engage and perhaps the higher temp does strange things to the pressure / sensor. If you've not had it done for a few years, it's well worth the £50 or so that it costs.