A Line Mechanic reports a CRJ-200 required an Air Turnback when the flight crew did not have a standby altitude or airspeed SA/IAS reading. Mechanic had left the Pilot and Co-Pilot's mach transducer selector valves in the 'Closed' position after working a previous standby airspeed discrepancy; because water had filled the standby pitot drain line.

Narrative

I received a gate call on a CRJ-200 for an incorrect SA/IAS Airspeed reading. I inspected all Pitot/Static drains. I found P3 drain line to be full of water. I informed my Lead of the situation relating to the discrepancy. I prepared the Standby Pitot/Static system for purge of water contaminants from pitot lines. I selected both MACH TRANSDUCER SELECTOR VALVES from the NORMAL POSITION to the CLOSED POSITION. While reviewing if steps were skipped or missed; it was discovered by myself that the MACH TRANSDUCER SELECTOR VALVE was not selected from the CLOSED to NORMAL Position. The event occurred due to too much conflicting information in regards to the P1/ P2/ P3 MACH TRANSDUCER Protection systems. Time constraints were placed onto the SA/IAS discrepancy; to expedite the return of the CRJ-200 to service at XA:30 HOURS. I later reviewed all associated AMM material information relating to the mistake. I suggested an open Aircraft Logbook item be made; stating that Pilot and Co-Pilot MACH TRANSDUCERS SELECTOR VALVES are placed in the CLOSED POSITION. The open Logbook Entry would prompt all Maintenance personnel to provide a corrective action stating; 'Pilot and Co-Pilot MACH TRANSDUCERS SELECTOR VALVES are placed in the NORMAL POSITION in accordance with (IAW) the CRJ-200 AMM 34-11-00-860-012'. Another suggestion would be the placement of bright colored streamers or tags; placed onto the MACH TRANSDUCER SELECTOR VALVES in the cockpit; indicating that the valves are in the CLOSED POSITION.