Our Enclave has a hissing noise coming from the ac system. When it hisses the temperature fluctuates from around 41 degrees and will go as high up to 58+ degrees. This is super frustrating. The dealer has already replaced the compressor and the expansion valve. Because the the GM engineering team can not identify this issue is out of any parameters, they are declining to assist further. They did admit that there are others like this to the service manager, but do not have a fix. I was told by GM customer service to find another dealer and see if they can identify anything different. The hissing and temp fluctuation is NOT normal. I can not see where anyone who had this going on would accept this as normal. Any advice is appreciated. I do have video recording the sound and temp fluctuation, but the file is to big to upload.