Can anyone tell me if it is bad for the air conditioning to shut down the Cummins when the A/C is still on?If so, why?Does anyone know why my 93 CTD would be getting better mileage at around 365,000 miles than before?I used to get only 465 miles average down to a quarter tank. Recently I'm getting around 535 miles when down to a quarter tank. Is it just broken in?T.I.A.

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Can anyone tell me if it is bad for the air conditioning to shut down the Cummins when the A/C is still on?

No. No harm will come to either the engine or the A/C. Just that you might get dog's breathe after awhile from mildew that might form in the A/C evaporator. Typically its a good idea to shut down near home and let just the vent blow to dry the evaporator out a bit. But even that will not cause any harm just funky smell.

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I used to get only 465 miles average down to a quarter tank. Recently I'm getting around 535 miles when down to a quarter tank. Is it just broken in?

Could be... Or there could be other things going on that might of worked in your favor... Fuel differences, weather / climate is warmer, driving style change, etc.

she is good and broke in....and if you are just now getting better fuel mileage..i am gunna say you live up north somewhere and all of the winter blended diesel is finally gone..winterized fuel equals LESS m.p.g's:thumbup2:

Really can't tell MPG without hand calulating the odometer / fuel fills. Has there been a tire changes, changes in driving?