This is what scares me about doubles

as carl said defrost off ,

 

Defrost off, crack a window. Volvo tractors if he drives those the VN200 model is notorious for fogging up.

 

Thanks everyone, that makes a lot of sense. He often calls me to touch base when I'm at work in the morning and he's on his way home so I'll tell him what was discussed here and see what he says. He's driven a bunch of different trucks since May, Volvos, Internationals, Kenworths etc. I have the impression they have mechanical problems fairly often and he has had to deadline trucks for repair a number of times, I guess because those trucks are used by the P&D drivers during the day as well. Don't know if he was in a Volvo last Friday, I'll ask.

 

Also agree with keeping the defroster off. But that trick only works when it's well below freezing. The windshield will freeze clear and snow will bounce off of it without sticking.

Btw, nice of you to come on here to look out for your son. I wish him the best. Should tell him to set up an account here and so he can ask any technical questions he might have. Lot of good people on here giving good advice.

 

I agree with these guys, @Evie3 . It seems like the defrost is really only good for sitting still. When rolling at certain temperatures you can end up with a big chunk of ice on your wipers, making them completely useless. As was also said, window cracked. The rationale I heard for that was to not let the cab heat from the floor vents warm up the windshield either.