I recently purchased an Acura Legend, my first car. I was told by the buyer the air conditioning was fixed, however it gave out and blew only hot air. I took it to the shop that had changed the decompressor and they stated the problem was a valve and that it would cost $54 for the part and $330 for the labor. A week after taking it into the shop the car began to have this whistling noise upon turning on the engine. It was low at first, but now it is loud and occurs at a higher frequency. However, when I drive on the highway, the sound disappears once I get off of the highway. Furthermore, the sound used to only occur when slowing down, but now occurs during low acceleration.