Maintenance Airframe; Maintenance Powerplant; Maintenance Avionics
Confusion; Distraction; Troubleshooting; Situational Awareness; Training / Qualification
Aircraft Equipment Problem Less Severe; Deviation / Discrepancy - Procedural Published Material / Policy
General Flight Cancelled / Delayed; General Maintenance Action
Aircraft; Human Factors; Procedure; Manuals; MEL
An Airbus aircraft had Vent Blower Extract Fan Circuit Breaker popped. Circuit breaker that was popping was for Hi-Speed Fan; troubleshot to Fan Blower. So we had one and Removed and Replaced (R/R) Fan Blower. Performed Operational Check and got all indications in cockpit which are Flow Bars that switch from inboard to overboard when you pull circuit breaker for Flight/Ground; which tells you which fan is working; Hi or Low speed. Since I got the flow bars I assumed both [fans] were working and I was done. Had I waited at least two minutes between checking the Hi and Low Speed Fan I would have got the warning. It takes a few minutes to get the warning. Maintenance Manual tells you the fan will go to Low-speed; but hard to hear in the cockpit so you look for flow bars. What happened is that I assumed that both fans were working because [of] the indications and I did not reversed the MEL process [procedure] and double check myself. We decided in our Shop that a second person will check the reversal of the MEL. Avionics cooling. Gate turnback.
A Line Technician reports that an Airbus aircraft returned to gate after he had replaced hi-speed fan blower for popping the vent blower extract fan circuit breaker. The vent blower fan had been on MEL deferral.