B737HT,
Here is the answer from BOEING ENGINEERING on your PACK NNC question:
In the PACK NNC , the effect of the recirculation fans is optimized if only the right fan is operating because the fan motors are a heat source.
The left recirculation fan draws air from the area immediately around the mix bay while the right recirculation fan draws air from the "horseshoe duct" beneath the forward passenger cabin. Operation of the right recirculation fan promotes airflow through the grilles in the forward passenger cabin and better ventilation is achieved with the right fan than with the left.
Also,
The step to turn off the left pack may soon be removed as it already has been removed from the master QRH for the -800 that Boeing uses. Not sure when that will be sent to the operators.
Basically what i wrote in my post #3.
Now concerning the MYTH,non sense FCOM misinterpretation of extra fuel consumption by turning OFF the recirculation fans that Cosmo keeps on blabbing about,here what BOEiNG ENGINEERING via General ELECTRIC have to say:
According to GE and our flt ops engineering department there will be a slight increase in TSFC when the fans are turned off due to increased bleed air demand from the engines. Just as you expected.
Best regards,