OK, all you auto wizards. Have an '03 Dakota 4x4 QC Sport, 4.7L-V8, AT, A/C, PS, PW, Cruise, etc..

Gas mileage seems to have dropped quite a bit. Had a brake issue - replaced rotors & pads on the front end last weekend, great now, assume no dragging brake.

Every time I turn on the Defrost vent or Def./Floor vent, I seem to get pretty cold air thru the Defrost vents. Yet when I turn on the floor or dashboard vents, all OK, normal outside in air flow, and according temperature (ie. not cold in summer).

Every time I park the truck in the driveway in summer, without using A/C, it also drips like a son of a gun for a short while - hear it kind of "hissing, or steaming" onto something in the rt. rear (pass. side) of the engine compartment, and water all over the driveway or road. Am assuming that the A/C is ON/running (even without it turned on), and this may be the condensor condensation (unintended pun) dripping onto either the manifold or the exhaust pipe out at rear of the engine.

Any thoughts folks ??? I'm sure I'm taking a hit in mileage due to this being ON all the time. Also have heard a bit re. replacing "resistor packs" under the dash on the passenger's side in the cab.

Please - can all you t-shooters lend me some advice or resources to look into ? Ever heard of this type of thing before ?? And I DON'T want to have to start replacing worn out A/C parts due to over, unneeded use!

Thanks, Kevin in VT

 

Yea mine has the condensor drip right on the exhaust manifold as well. Great design *sarcasm*

I have't tried defroster...My full speed fan on max cool isn't all that cold either, grnted my rear window is missing it's seal...

 

Yes the defrost uses the a/c.

 

Is this true - is the Defrost, when just "opened up," have the AC on all the time ??

If so, this a REAL GREAT design!!!! I'm a mech. eng. and wouldn't have done THIS! WTH ?

Is the AC realy on all the time regardless, and is ported into the cab with the Defrost when it's opened? I don't seem to remember this in the past. I DO remember opening the Defrost vent and getting the "normal outside air," cold OR hot OR in between, into the cab.

Anyone clear this up for me/us ?? Any knowledge of either the "problem" or if it truly by design (Chrysler) ?

Thx, Kevin in VT

 

The ac runs to dehumidify the dampened air in the cabin. That is the reason you need the defrost in the first place in most cases. The humidity level inside plus the temperature differential with the outside air fogs the inside glass. Your body gives off moisture adding to the problem also. All of this takes place in a relatively confined space so the humidity level can get rather high. Ever driven a vehicle without air on a damp morning? Can be a real SOB to clear the windows and usually you resort to running the heater to evaporate the condensation. The system is working as it was designed and this design is common to most manufacturers. The ac compressor running during the colder months is actually beneficial to the system as it keeps the system lubricated. If you live in a damp climate or where it rains alot this is to be expected unless you just run the vent and wait for results. If any water is getting into the cab by way of a leak or even on your shoes the problem will be worse. If you've always had to use the defrost in the past and the mileage dropped the problem is not the ac compressor running although it will use more gas if you've used it all the time the mileage drop problem is elsewhere.

 

Thanks for the explanation "deranged!" I'm not surprised, and what you noted makes sense. I guess I just thought that the a/c shouldn't be ON if it wasn't officially "turned on" (the orange/amber push-button, rt. side of the controls panel is not depressed). Hmmmmmm. Maybe my O2 sensors are going south ? just turned 100k miles on the OD, haven't ever changed these, tho' am darn good about plugs, top end gas system cleans, TBI cleanup, oil/filter, and most other things. Again, more thoughts re. lower gas mileage appreciated!

Kevin in VT

 

Excellent explanation I would have taken me 3 pages to get that point across