TurboABA
Top Post Dawg
Ok... I can see the higher gearing "helping", but are you calculating your new MPGs by factoring in the new circumference? You are now covering more distance than what your odo is reporting.
right!?I'd like to retract that statement... I just read your sig.....
So in your quest for improved FE, you've gone to larger wheel diameter, heavier aftermarket rims, and jacked the vehicle up to increase drag?
Very interesting.....
I may be wrong, mainly because I stopped trying to be anal about FE years ago.... I rarely even look at pump prices.... I just fuel up when I need to, and reset my trip meter each tank... unless there's a massive deviation that causes me to think something is wrong, I don't stress about the fluctuation.... way too many variables.......The vehicle is higher than stock but sits more level than stock (raised the front) BUT overall I get better MPGs with the bigger tires than the smaller factory wheels .... I guess the overdrive effect of the larger tire diameter more than offsets the aero losses ( I am about to go oven bigger wheel wise in a couple weeks (NOTE : I had a typo in my sig .... my current tires are 205 75 R15 and I will be going to 215 75 R15).
Andrew
HiOn a Mk4 the only real efficiency gains I could see are turning the blower fan speed down, or using recirculate. The system is always going to target a ~38*f evaporator temperature. But once it gets close to that temp the compressor is going to unload. Yes, if it's a not-so-hot day you'll probably want to mix in some waste heat from the engine. But who cares? The system is still doing full dehumidification. If it's temperate out and you feel you need the AC it's probably humid, so you want the evaporator cold. Trying to have a 50*f evaporator cool you off will feel super clammy, and not defrost the windows.
If you want a system that has a variable evaporator target, get a Mk5 or newer. They are a bit more efficient than the older cars, but the Mk4 system is fairly good for efficiency.
IIRC the clutch used on the Mk4 is not designed for constant cycling, and doing that will burn it up. Repairing that will cost a lot more than any fuel saved.
Another thing you can do is make sure your condenser, radiator, and evaporator are all completely clean. Including the space between the condenser and radiator!
Yes, I was a little concerned about that (the freezing of the evaporator without enough airflow over it) ..... I wonder how one can tell when it freezes up into a block of ice? ...Might have issues with the evaporator freezing up without enough airflow over it.
Your gains if any will be almost immeasurable in my opinion.
Do your older vehicles have a variable displacement compressor? I'm guessing no (unless they were 4 cylinder GM vehicles). An R134a VW does not have a cycling clutch. The ECU might turn off the compressor clutch when you pull away quickly in first or 2nd gear, but otherwise the clutch remains on.on my older vehicles i can definitely feel AC compressor switching on and off ... with the jetta not really ... I'll have to pay closer attention to it next time I drive.
HiDo your older vehicles have a variable displacement compressor? I'm guessing no (unless they were 4 cylinder GM vehicles). An R134a VW does not have a cycling clutch. The ECU might turn off the compressor clutch when you pull away quickly in first or 2nd gear, but otherwise the clutch remains on.
The evaporator should also never freeze, because again it's a variable displacement system... so as the evaporator temp (and therefore the suction side pressure) goes down, the compressor unloads and reduces its displacement to keep the evaporator from getting too cold.
Airflow over the evaporator is the primary thing that will load it down. Temperature and humidity are secondary. A blast of 75* air will load the system down more than a wisp of 85* air.
The first speed of the fan is already fairly low. Remember that airflow through the HVAC case also cools the blower motor and its speed control resistor. If you go too low the fan might stall, and overheat.
-J
HiOn my 2003 ibiza which is the next generation up from the mk4 golf climatronic system.. The evaporator temperature setpoint is variable. (along with variable displacement compressor)
Can range between 2c and 11c (highest I've seen) depending on humidity/temp requirements.
It's really quite a good system, even when it's 25c out (OK not that hot but warm enough for AC) it will throttle back to 6-8c evaporator temp.
If the mk4 golf evaporator temp stays the same, then I suggest a better way than reducing fan speed will be to make the evaporator warmer.
I believe its an NTC thermistor on the evap, so as temperature increases, resistance decreases, so adding a small value resistor in series will make the car think the evaporator is colder than it is, and throttle back the compressor. (perhaps use a potentiometer and adjust it on the fly as you drive)
Having decent airflow through the cabin is a must for comfort, and with most of the load likely being taking humidity out of the air, reducing the humidity load will save more energy than dropping fan speed to a trickle.
The wind effect on you will make it feel cooler with less energy aswell
You should add a Poll Question to the top:I have to order the resisters now and hopefully we should be good to go (well except for the most complicated part ...actually figuring out how to splice it in wiring wise ) ha...
I really hope this is sarcasm. Because thats too good man!!For those blessed with the pano sunroof who don't use it (me for one), I bought some foil-faced insulating material from my local Big Box (Lowes). I cut a fitting panel and slipped it between the sunroof glass and inner headliner. It made a huge difference in my air conditioner performance.