The Cascadia Evolutions have the Idle Free HVAC system that produces 10-12 hours of cooling and the Aspar heater that produces unlimited heat. Here's a picture of my APU:
Depends on your region. Currently only the southern fleet have them and total about 400 truck. They are a pia to fix. Its a sealed unit to replace the whole cabinet behind drivers seat has to be removed. Sent from my Galaxy Nexus using Xparent Cyan Tapatalk 2
I've never had trouble staying warm in my company truck - well the Cascadia anyway. The old beat up Century I started with had some issues with the bunk heater, but the one in the Cascadia would roast you right out of the bunk. Staying cool was a little bit of of a challenge in early spring and late fall when the outdoor temperature may be below 70* (can't idle) but the sun beating down on the cab really warms it up inside. After that though I had no trouble idling to stay warm, and the exhaust dumping under the cab always kept the sensor nice and warm lol.