Came across a set of makeup air units today, both with DJE controllers. Each unit has a direct fired burner, as well as a chilled water coil. Each unit has mixing dampers, that is a set of return air dampers, as well as fresh air dampers that modulate via a bellimo damper motor. (as one opens the other closes, like an economizer)
I have never seen a makeup air unit with return air. Both of the units had the damper motor disconnected. The wiring diagram indicates a "mixing damper signal 4-20 mA provided by others" which is nowhere to be found. So right now you just set the damper position by hand.
What is the purpose of providing return air to a makeup air unit? What should be signalling the dampers to move? Why would you want that? The whole thing has me scratching my head.
This is for a new customer, and the original call was for no heat on one of the units (which has been fixed). But I would like to know more about these units.