Q. Left my puppy in the kennel for an hour. When we came home his bark was weak, and his breathing sounds weird
A. Probably because he was screaming the entire time. You must gradually get the dog used to being alone without you. Introduce the crate slowly in baby steps. First place him in there for only a couple minutes with a high value chew. Then place him in there for naps. Be very slow about it. He should have been comfortable with being in the crate for hours with you present before leaving for an hour. He should of also been tired and ready for a nap with a high value chew while you were gone.