B737-800 pilot reported the aircraft abruptly pitched up while doing a flight control test and the aircraft was almost uncontrollable. According to the reporter Maintenance had performed incorrect work on flight controls; possibly due to inexperience with the aircraft.

Narrative

FCF (Functional Check Flight) for manual reversion. During flight control confidence check when going from A flight control switch to on and B off; plane abruptly pitched up and gained 200 ft. Switches were immediately restored; but plane was almost uncontrollable. Data afterward showed almost a 2.0G pitch up and 100 lb. of CA (Captain) down force and 55 lb. of FO (First Officer) down force. Data should be verified by Maintenance. We are lucky we didn't snap an elevator cable as Boeing states if you apply pressure on the yoke when applying hydraulic pressure an elevator cable can snap. We had 2 events with the same pressure applied. Months later I question if Maintenance checked the cable for early fatigue. If not; should this plane be checked now?Maintenance incorrectly rigged elevator stab and flight control switch panel had a switch that did not fully close; so we were in manual reversion prior to the steps in the procedure. Second flight had same issue as Maintenance only fixed flight control switch panel. 3rd flight issue was corrected. A hangar that traditionally worked on wide body aircraft did the rig. Inexperience on the 737 was a factor. Keep the same hangars doing the work on the 737 that always have done them. Bring in experienced technicians for flight control repairs to oversee work.