I think you may need a total diagnostic. Anyway, I had a similar problem also with Toyota Premio and I was searching a lot for a solution. I was at different services with a hope they could help me. I was searching on google, asking my friends, relatives and acquaintances but nobody could help. After a while my father founded reliable and professional aircon technician that could solve my problem. My car is very important for me, because I want it to be in a good condition. I should feel comfortable because I adore to travel by car, we usually do it with my family.