Mitsubishi Strada 2007, 4x4 Diesel, M/T.

Having issues with my car aircon lately. First when it stays still like in traffic, after a miunte or two the air coming out of it becomes hot. But when the car moves like 30kph/h everything goes back to normal. Its just when its idle. specially in the hot mornings to afternoon. its unbearable. I have the a/c cleand a year ago. cleaned the filter and added freon. But it was still the same. Now its getting worse. In addition of hot air coming out of the a/c after few seconds you can hear a loud sound i don't know how to describe it but its like a "lady screaming on top of her lungs on a high pitch". then i would just turn of the a/c and it stops. but when i do turn it back on while the car is still. the same thing happens. Do you guys have any idea whats happening?

Im looking for a credible shop yet affordable in Quezon City. And if possible an idea on how much im going to spend to have it fixed in general. I have read some thread here and im considering Frigid Zone in congressional ave. But i need 2 more for comparison of prices.

Thanks in advanced for any feedbacks! I would really appreciate it.