vicestan

Does anyone know what the normal preasure should be in the a/c system, I recently had my evaporator core and expansion valve replaced and just recently I filled the system up with freon. Now since Ive been driving with out a/c for more then a year now on my gs I forgot how the engine sounds but now im getting this whistle sound, kinda like im running a super charger or the srt air intake. Its weird because when the car was at idle I gave it some gas and brought the rpm up to about 3k freon started coming out from under the hood and it was like a small cloud and all, im really worried b/c I think there is a leak in the line somewhere. Does anyone know how much lexus dealership will charge to check the system? I mean I just had the evaporator core changed not at the dealership though but I still have it, I might even bring it along maybe they can give me some lean way or something, and if the dealership is not the best place to go where do you guys recommend I go to get it checked for leaks?.