Well, after some experimentation, I figured out the reason that newer model Freightliners without a dedicated thermostat are full of fail.
It is very simple, really.
When your thermostat is ALSO your air output temperature control, somebody made a retarded design decision.
Timers don't even matter here. Combining thermostat and output temperature into one setting fails on the most basic level of thermodynamics.
Here's why. Removing heat from a system is not linear. The greater the temperature differential between the current temperature and the input temperature, the faster the current temperature will change.
By combining the thermostat and the output temperature control into the same device, the Opti-idle system will ALWAYS cool to the desired set temperature very slowly, because the output temperature of the air from the cooling system gets closer and closer to the desired setpoint temperature.
I tested this during a 34 I just took.
Every single day before my 34 I closed the curtains after cooling the bunk and cab to a cool temperature, then set the thermostat to 70 degrees or so. Every single night, opti idle failed after the first time it ran.
During my 34, I kept the curtains open between the cab and bunk, and used the front curtains, making sure to keep the airflow from all the front vents clear.
With the cab AC and sleeper AC running, I turned the cab to max cold, and the sleeper to 70 degrees. (70 degrees is straight up, and is supposed to keep the truck between 67 and 75 degrees.
Opti Idle worked perfectly with the air mixing between cab and sleeper.
The temperature monitoring comes from the sleeper controls, so the cab controls can be set to max cold, and the cab vents will do most of the work while the sleeper vents barely do any heat transfer at all as the air in the sleeper approaches the set temperature.
Quite simply, Freightliner's removal of a separate thermostat to save 19.99 from the cost of building their Opti Idle trucks has led to a basic thermodynamic design failure.
It's all in the heat transfer curve.