A Captain reports when he turned on the 'B' (electric) hydraulic pump to perform a flight deck Check for the first flight of the day; the flight control wheel turned full deflection left. After turning off the hydraulic pump; the control wheel on their B737-400 remained full Left.

Narrative

I arrived at aircraft and proceeded with flight deck check. It was the first flight of the day and it was very cold outside. When I turned on the 'B' Hydraulic pump; the flight control wheel turned full deflection left. I turned off the pump and the control wheel remained full left. I tried to bring the control wheel back to neutral but was unable to move it. I thought the cold weather may have something to do with it. I called Maintenance. They looked over the problem and were not sure what was going on. Upon going outside; they found the Spoilers up on one side. I got out of the way and let Maintenance do their job. Turns out Maintenance was on the aircraft overnight and some how moved the aileron trim control full left which caused the problem. I did not think to check the trim because we never move it much and there is no gauge to check the setting except the markings on the control wheel. I had not put anything in the Logbook. Maintenance Supervisor said to let it go and not write it up because nothing was wrong and we had not left the gate. The Supervisor said they would take the delay. I should have written it up. Maintenance working in cockpit at night. Don't touch anything unless you need to.