I had this problem with my 2.6 liter engine and it was determined to be the belt tentioner. When you hear the squeal the belt is slipping and the rpm sensor in the back of the ac compressor gets out of sinc with the engine sensor and shuts off the ac compressor. That is why you are blowing cold until after the squeal then it blows warm. When that happens, pull over and shut off the engine and restart, it will resinc all sensors and your ac should blow cold again.

Try checking out the tentioner first, sound can play funny tricks on you while you are driving.

Let me know how it works out.

Sincerely,