Bought a new dometic a/c and it won't run.

bought a new dometic a/c and it won't run. voltage is present in the control box until the upper unit is plugged in/connected, to the control box/thermostat. the voltage to the upper unit then disappears like it's shorted or grounded.
prior to plugging in the upper or main unit there was 110v a/c present
on the lo and hi fan terminals as well as the output to the female
plug for the roof unit. when plugged in the 110v is no longer present on any terminal of the control box or thermostat.
any idea what may be causing this problem?
Joel from Florida