Proair 1100 A/C unit

[dakazman]

  I need an Ac expert.
   My GMC van with dual AC system that runs on one compressor is blowing full cold 43f on the main and hot in the rear unit. I’m going in circles trying to figure out how the rear unit is stuck in heat configuration .  Could it be a stuck vacuum switch? The rear unit supposed to blow hot only when controls are in the floor position.
 Dakazman