Air Con Not Working When Hot????

[NEZ]

hi,
does anybody have any ideas?

my aircon is fine when first used and seems to work until the engine temperature or the outside temperature gets hot, ie, on a hot day it will work fine for around half hour tops, then it will cut out and just blows normal air as if the air con was turned off?

is there a cooling fan or something that is at fault maybe?

any ideas??

thanks