This may put it in perspective. I just took a road trip thru some hot country in my F250 7.3L diesel that has no AC. When it got over about 75F outside, when we stopped for a short time, and restarted, the fan would blow hot air into the cab from the heat built up in the heater box. The fix was to put a valve in the heater hose. That kept that blast of hot air from cooking us on startup. It did help with comfort.
