2nd Gen Non-Engine/Transmission Fuel economy loss with defroster on

[SMcGrady]

I noticed a little bit of water dripping from the passenger side of the engine compartment, forward of the firewall. After searching the forum I found a few posts that said that when the defroster was on it caused the A/C to be on or cycle, or something?? and this would sometimes cause condensation to drip from this area. I believe this is my problem as it is water, not coolant, that is dripping.



(Here comes the dumb question... )



This made me wonder about fuel economy. I believe that it is true that running the A/C will cause your fuel economy to suffer a bit. So... if running the defrost causes the A/C to run in some fashion, will this too cause my fuel economy to suffer as well?



Thanks,

Scott-

 

[ToolManTimTaylor]

Indeed the compressor runs as to truthfully and effectively defrost or defog a windshield warm DRY air must remove moisture from the window. All an ac system is is a simple dehumidification process. Now the suffering in fuel mileage is the same as if you were running your ac. How much loss . . 1 maybee 1. 5 mpg. The Cummins barely notices the parasittic loss of an ac compressor on our trucks as running torque produced and is always on tap so no fuel adjustments are required like a gas engine.

 

[LRutigliano]

Our trucks run the Sanden AC compressor. Go to [http://www.sanden.com/support/pdf/SD7_brake_curve.pdf and you can see the power curves of the compressor. Depending on engine speed, its about 3 to 7 hp.



Compared to the power our mighty Cummins are producing, the power for the AC compressor is very small. Also, its not running 100% of the time except maybe on very hot and humid days. In the winter time with defrost mode, its probably ON about 15sec for every minute of run time.

 

[jkidd]

thanks for the info on the compressor

 

[SMcGrady]

Great answers, this forum rocks!

Thanks,

Scott-