Commercial Fixed Wing
Flight Crew Instrument; Flight Crew Air Transport Pilot (ATP); Flight Crew Multiengine
Flight Crew Last 90 Days 185; Flight Crew Total 8159; Flight Crew Type 5491
Situational Awareness; Distraction
Aircraft Equipment Problem Less Severe; Deviation / Discrepancy - Procedural Published Material / Policy
Flight Crew Overcame Equipment Problem
Environment - Non Weather Related; Human Factors; Aircraft
Received aircraft from maintenance base in ZZZ with AFT FUEL BOOST PUMP MEL.  Called and got another Dispatcher to patch Captain to Maintenance Control.  Still did not get my answer about having to carry an extra 5;000 pounds of unusable fuel.  Flying with a First Officer who was on different aircraft.  Very little recent experience in aircraft; because of the COVID and personnel issues.  Slowed pace considerably to accommodate; First Officer [was] very hard on himself and working hard on flows; but not smooth and habit like.  Dark on departure; and with amber fuel pump light shining in my eye; I did not catch the switch out of place after the Before Takeoff Checklist was done and we took the runway for takeoff.  Got the tattle tale message after takeoff and debriefed the situation.
For breeze-on/reduced thrust takeoff from Runway XXL at ZZZ; we set and left L PAC switch on high position.  While climbing; we received ACARS alert message for incorrect pack configuration. We immediately corrected the problem. We continued the flight then landed ZZZ1 without any incidents.
Air carrier flight crew reported departing with an incorrect pack configuration.