General 08 CR-V Questions

[XboxEboy]

Just took an 8 hr (!) trip to Atlanta.
Great news...going 72, with the AC on, and with the roof rack installed, we still averaged 29 there and 28 back! It's also the AWD model :)

But, along the way, I wondered two things:

If you have the AC on the coolest setting, does this use more gas than if it were on a setting that blended warm air? Does it use more freon? Or, does it just mix in engine warmth (like the heater) so the temperature setting doesn't have an effect...just having the AC on (no matter the temp) will use more gas than not.

Also, being All wheel drive, does this mean the 4WD only kicks in when it needs to, or is it always in 4WD? If not, is there an indicator light that lets you know when 4WD is in use?

[tsmithvt]

But, along the way, I wondered two things:
If you have the AC on the coolest setting, does this use more gas than if it were on a setting that blended warm air? Does it use more freon? Or, does it just mix in engine warmth (like the heater) so the temperature setting doesn't have an effect...just having the AC on (no matter the temp) will use more gas than not.
Also, being All wheel drive, does this mean the 4WD only kicks in when it needs to, or is it always in 4WD? If not, is there an indicator light that lets you know when 4WD is in use?

Right. Any time the compressor clutch is engaged it's pulling torque from the crank shaft that can no longer be used to drive the car. If you want to drive at the same speed as before, it will take more fuel. How much the compressor is engaged (cycle rate) is determined by a host of factors from your temp setting to the heat load on the vehicle to the speed the engine/compressor is turning.

The RT4WD System is an "On Demand" type system (self contained, hydromechanical). Simply put, the system is "operating" all the time but only provides torque to the rear wheels (engages) when the front wheels have a detectable "slip rate" (start to loose traction). There is NO indicator (light or other) to confirm system operation. A VSA engagement indicator light probably means that your RT4WD System has also engaged but it's not a guarantee. The best confirmation of system operation is plowing through a snow bank, emerging on the other side and continuing on your way with a big smile on your face.:D

More detailed explanations of operation can be found at:Honda CR-V Owners FAQ - CarSpace Automotive Forums (http://townhall-talk.edmunds.com/direct/view/.ef229e9/0)
(paragraph #10 on)

Honda Media Newsroom Release: 2007 Honda CR-V - Powertrain (http://www.hondanews.com/categories/844/releases/3653)

Google Image Result for http://www.motiontrends.com/2006/m09/Honda/CR-V_gen3_multi_plate_clutch.jpg (http://images.google.com/imgres?imgurl=http://www.motiontrends.com/2006/m09/Honda/CR-V_gen3_multi_plate_clutch.jpg&imgrefurl=http://www.motiontrends.com/2006/m09/Honda/CR-V_SUV_engines.shtml&h=298&w=400&sz=18&hl=en&start=393&tbnid=u6gy681arpPriM:&tbnh=92&tbnw=124&prev=/images%3Fq%3Dhonda%2Bcr-v%26start%3D380%26gbv%3D2%26ndsp%3D20%26hl%3Den%26 sa%3DN)

[pepollock]

At highway speeds you will get slightly better gas mileage with the A-C on and the windows closed, than with the windows open. Aerodynamics suffer with the windows down. At in-town speeds the opposite is generally true but that's when you really want the A-C on since you don't get a lot of breeze through the windows at slow speeds. The compressor cycles on and off based on internal system pressures. Sitting at a stop light you can feel and hear it click on or off and the engine responds through an "idle-up" control that tries to keep idle speed constant. On the move you probably won't feel the compressor kick on and off but it is happening, and raising or lowering the temperature control does not affect it. The dashboard temp control only adds some heat from the engine to mix with the cold air from the A-C. Unlike making the air cold with A-C, using heat is free. The heater uses waste heat from the engine.

[XboxEboy]

At highway speeds you will get slightly better gas mileage with the A-C on and the windows closed, than with the windows open. Aerodynamics suffer with the windows down. At in-town speeds the opposite is generally true but that's when you really want the A-C on since you don't get a lot of breeze through the windows at slow speeds. The compressor cycles on and off based on internal system pressures. Sitting at a stop light you can feel and hear it click on or off and the engine responds through an "idle-up" control that tries to keep idle speed constant. On the move you probably won't feel the compressor kick on and off but it is happening, and raising or lowering the temperature control does not affect it. The dashboard temp control only adds some heat from the engine to mix with the cold air from the A-C. Unlike making the air cold with A-C, using heat is free. The heater uses waste heat from the engine.


So, in other words, with all else being equal, I will get the same gas mileage with the AC on whether it is set to the coldest or the warmest setting?

[kinoav8r]

So, in other words, with all else being equal, I will get the same gas mileage with the AC on whether it is set to the coldest or the warmest setting?

Yes.

If the AC is ON, it's ON. The compressor clutch is engaged and your mileage will drop.

Turning the temperature setting up increases warm air added to the cold from the AC. The warm air is free - it doesn't hurt your mileage.