FLT CREW OF B737-900 ARE UNCERTAIN OF OPERATIONAL PROC FOR AIR CONDITIONING TRIM AIR SYS MEL ITEM.

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I WAS GIVEN AN AIRPLANE TODAY. IT HAD A SINGLE MEL ON THE RELEASE FOR THE TRIM AIR SYS. THIS IS THE MOST CONFUSING MEL I HAVE BEEN CONFRONTED WITH TO DATE. WE CHKED EVERY PAGE OF THE MEL THOROUGHLY. WE SPOKE WITH MAINT NUMEROUS TIMES. FIRST I WAS ASSURED THAT THE R PACK AND R RECIRCULATING FANS SHOULD BE POSITIONED TO 'HIGH' AND 'OFF.' NEXT I WAS TOLD TO OPERATE THE SYS NORMALLY; JUST NOT TO CLB ABOVE FL250. THEN I FOUND THAT THE HIGH/OFF METHOD WAS THE ONLY ONE THAT WOULD WORK AND KEEP THE EQUIP COOLING EXHAUST 'OFF' LIGHT OFF. THEN THERE IS THE LIMITATION IN THE FLT HANDBOOK TO NOT OPERATE A PACK IN 'HIGH' FOR TKOF; APCH; OR LNDG. ATTEMPTING TO COVER ALL THE BASES IS PRACTICALLY IMPOSSIBLE. THIS MEL NEEDS ATTN. I WOULD RECOMMEND A GROUP MEETING WITH THE MAINT CTLRS INVOLVED; FLT OPS AND A B737 INSTRUCTOR OR TWO TO HASH THIS OUT. SUPPLEMENTAL INFO FROM ACN 626517: IN THE END; AFTER NUMEROUS DISCUSSIONS WITH MAINT; WE FLEW THE ACFT WITH BOTH PACKS IN 'AUTO' FOR TKOF; APCH; AND LNDG; AND PLACED THE R PACK TO 'HIGH' FOR ALL OTHER PHASES OF FLT. HOWEVER; THERE IS NO MENTION OF THIS CONFIGN IN EITHER APPLICABLE MEL FOR OPS PROCS; ONLY IN THE MAINT PROCS. AGAIN; VERY CONFUSING.