Maintenance Powerplant; Maintenance Airframe
Other / Unknown
Aircraft Equipment Problem Less Severe; Deviation / Discrepancy - Procedural MEL / CDL
Flight Crew Returned To Departure Airport; General Maintenance Action
Aircraft; MEL; Procedure
[Maintenance Technician] called in the Pre-Departure Clearance (PDC) for Aircraft X and that he had one defect in the logbook. Reported all lavs would not flush. There was water sprayed when the button was pushed but there was no vacuum. I told him it sounded like the Vacuum Blower was not working and to check 2 circuit breakers on the P91. The Vacuum Waste Blower and the Vacuum Waste Cont. He reported both breakers were set. I had him then check that the service doors were closed and they were. It was concluded to go ahead and put the Blower on MEL because other than no vacuum; the lavs operated normally. Looking at the MEL; I instructed [the Maintenance Technician] to pull and collar the 2 breakers he had previously checked. This was part of the Configuration Change Procedure in MEL 38-XX. While he was doing this; I emailed to his office the required placard to be placed on each of the lav doors. When [the Maintenance Technician] called back; we confirmed the 2 breakers that were pulled and I completed the logbook with him. We then completed the PDC and the aircraft was ready to depart ZZZ. [Later] dispatch was talking with Aircraft X and that none of the lavs were operating and that he was going to return to ZZZ. Knowing that I had just worked that issue; I looked again at the MEL and discovered that I had instructed [the maintenance technician] to pull a breaker that was supposed to be closed. This breaker; Vacuum Waste Cont; provides the power to each lav flush circuit and is required to be closed for the lavs to operate on the ground and in flight. This why the lavs were not operating. I spoke with the captain in flight and explained the situation and that his issue would be quickly resolved when back on the ground. After arriving back in ZZZ I spoke again with [the maintenance technician] and told him the situation and to remove the collar and reset the breaker. We did this and the lavs operated normally except for the vacuum function on the ground. An Overweight Landing inspection was completed as well as another PDC and the aircraft departed again with no further issues. It was a complete misread of the Configuration Change steps in the MEL. I would say the steps were hastily glanced over by myself instead of deliberately reading each word. What jumped out to me was the way in which the 2 breakers were identified: VACUUM WASTE BLOWER (F2) and VACUUM WASTE CONT (C11). In the MEL book; these names are directly inline horizontally and vertically with one another. The top one has you open the breaker but the one below has you verify that it is closed. Again; I just saw the 2 breaker names and knew I was making configuration changes by pulling breakers.  MEL Maintenance Procedure step should be removed from the procedure where it currently is and placed as a prior 'Note' or a 'Caution' since the step is more of an advisory to make sure that the breaker is closed than it is a step with a required action; especially when the previous step has the action of opening it.
I was directed by [maintenance] controller to pull and collar Vacuum waste controller Circuit breaker and Vacuum Waste Motor circuit breaker to apply MEL 38-XX. [Maintenance] control had found after the aircraft was in-flight that [Maintenance] controller had; in error; directed me to pull the Circuit Breaker and collar the Vacuum waste controller Circuit breaker which caused the LAV waste system not to work at all and the aircraft to turn back to ZZZ. The Circuit Breaker for the vacuum waste controller was not supposed to be pulled and collared as was thought from MEL 38-XX after reviewing the MEL with ZZZ; per [maintenance] directions I pulled both the Vacuum Waste Motor and Vacuum Waste Controller Circuit breakers. I had double and tripled checked with [maintenance] if these two circuit breakers were the correct ones to be pulled and collared before I finished signing the work off.
Maintenance personnel reported that the incorrect circuit breakers were pulled when deferring a Vacuum Waste Blower.