2006 Winnebago Outlook / E450 Cab AC issue

Blend Door Motor looks like this:

The square hole at the top of this pic is where the motor turns the blend door shaft to position it.
You said you hadn't used the RV for several months. Have you seen any signs of rodent activity or damage?

You should be able to monitor the positioning of the Max A/C aka Recirculate Door by crouching outside the passenger door and looking up/into the foot well while somebody changes modes to/from Max with the engine running. It's the silver "can" with the black "top" that has the white tube attached. Middle of page 3 in the BAT thread. You should be able to see its arm extend and retract as you or a helper changes modes.
But you get colder air in Normal than in Max. What I wonder now, is what happens when you select MAX. To my understanding three things should happen:
1. Power to Compressor Clutch
2. Recirc Door to Recirc (inside air)
3. Blend Door totally blocks air flow past Heater Core
The Blend Door shows at the bottom of the vacuum hose diagram. Notice that there's a dotted line from the Knob to the Door. NO vacuum line or actuator. That's because it's electrically controlled. Position of the Knob tells a little motor/gearbox, mounted somewhere on the HVAC cabinet, where to position the Blend Door.
Open the hood, look at the compressor clutch, and make sure it's engaged (the front of it spinning) in Normal, Max, and Defrost. Should NOT engage in Off and Vent.
So... Look at the Recirc Door (but I no longer think it's your problem), and Look at the Compressor Clutch. If the Clutch STAYS engaged in MAX, then suspicion points to Blend Door.

So to be clear, are you thinking that the previous work done, which resolved the AC going through the defrost vents under load, is now just not closing the vent to the outside air during max AC? I would love to have supporting evidence that their prior worked failed and they should fix it as a warranty item (albeit a year is probably longer than the warranty, just not sure). I am not very mechanically inclined but love the pics from your fix on the other site.

Suggest you make sure there's strong vacuum at the connector on the RED vacuum tubing under the hood. Then see if it's equally strong where it enters the cabin to connect to the HVAC controls, probably in the passenger side foot well.
I posted this RV.net threadand there's more detail in my BATauto.com thread
If you scroll through the threads you can tell what the bypass job your Ford guy did actually involves.
HOPEFULLY, Ford Guy installed a Vacuum Tank and a Check Valve. And hopefully the Tank has a leak, a hose has a leak, or the Check Valve has failed.
The vacuum "motor" for Recirc is down there in the footwell as Oldme stated. You can see it in my pix and tell by the white vacuum tube that it's Recirc by checking the vacuum diagram that's also posted.
Look all this over and let me know if it does you any good, or if maybe I can try to help you further.

There is still a vacuum problem.
Max on the Ford is like "recirculate" on foreign autos.
It keeps out the outside air and re-cools the inside air.

There is a vacuum motor on the door that is not closing.
It is located on the right - passenger - foot well area.

If your tech did not add a vacuum reservoir and check valve, you can get a self contained unit (reservoir and check valve) at Autozone and other for around $15.00
Dorman/Vacuum Reservoir
Part Number: 47076

The factory fix is to dismantle the Whole AC system and replace the reservoir and check valve. They"wisely" hid it in the the plastic housing for the AC on the passenger side in the engine compartment. They also have to recharge the unit after reassembly. Usually $900+.

This may have nothing to do with your issue, but I always thought the difference between normal AC and max AC was that normal AC is cooling fresh, hot outside air coming in to the cabin vs. cooler, recirculated air from inside the cabin.

Perhaps one of the air flow dampers under the dash is stuck in a closed or partially open or fully open position that it shouldn't be in.