Pace MBT 201 desoldering station Vac Pump runs constantly with SODR Tractor plugged in

When Pace MBT 201 has its SODR Tractor handle attached, Vac Pump runs constantly. Review of operators manual, the pump should turn on when small switch on Tractor handle is pressed and then run for approx 1.2 secs after switch is released. Ohm'd the switch inside handle and switch is NO and closes when pressed. I am thinking there is a control relay on the only PCB that is stuck ON. Has anyone encountered this problem before and determined the problem?? Any assistance would be appreciated OR does anyone have an actual schematic for this Solder Station?