How his boss is running the company is one way to run a company, but it is not the only way. It is "old school." It is lean harder and harder and harder on someone. The boss is berating him, harassing him, even calling him during and install and then complaining he is too slow. That is so bass ackwards. And, the boss should never hang up on him. His boss is trying to get better performance through intimidation. But you know what, respect goes both ways. I have a boss, who challenges me, but she also turns to me for advice. She values me and is growing me as a professional. You are not going to win with this guy. You need to be looking.You mentioned that you were not hired for installs. I'm curious, what your specialty is.
In situations like this I pray. I pray that either the situation will become harmonious or I will be lifted out of it. Having said that, while you are in this situation, you can be practicing to be the type of employee you want to be. If I were in the HVAC field, I'd be looking for someone like you.
P.S. I've been through rough patches like this and I've learned you cannot let it get you down. I know that sounds trite, but it's stupid to let a turkey like this get you down.