///// Making the Air Conditioning more economical /////

TurboABA

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Jul 24, 2010
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Kitchener, ON
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2010 Jetta 6spd MT, 2014 Touareg Execline
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.
 

compu_85

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Springfield VA
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On 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!
 

Mongler98

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98 Jetta TDI AHU 1.9L (944 TDI swap in progress)
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.....
right!?
very interesting in dead. must want to have his investments pay off somehow!
 

TurboABA

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Jul 24, 2010
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Kitchener, ON
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2010 Jetta 6spd MT, 2014 Touareg Execline
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
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.......

Anyways..... you're going the wrong way if you want to be that anal about FE..... running wider tires increases surface contact and results in additional friction, increases drag, etc...... raising the vehicle allows more air to get under it and to once again create more drag....

If I were you, I'd slam it, run pizza cutters on it, and put it on the biggest diet possible..... especially given your job\usage..... you might actually see a benefit with that kind of use pattern.

Regarding original topic concern.... I'd speculate that using the A/C is less of a hit on FE than driving with your windows down and A/C off..... just sayin.
 

Andyinchville1

Veteran Member
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Apr 7, 2016
Location
Virginia
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2003 Jetta TDI wagon, 5 sp, 226K miles
On 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!
Hi

Other than initially turning on or off the air conditioning system I don't really feel it cycling per se .... 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.

I thought I had read somewhere where the Volkswagen compressor operates in a variable fashion ( as far as how much compressing it does) as opposed to older systems that turn on or off making it more noticeable when the compressor is actually compressing because it's full-on or full off?

My goal with be able to slow the fan speed down more than normal was not to have to blend heat in and still be comfortable in the summertime without the inefficiency of blowing of the evaporator more than needed because that would cause the compressor to work harder trying to keep the evaporator cold due to blowing on it unnecessarily hard.

In the winter time it would be necessary to add heat because otherwise you would be cold.

I suppose in the winter time ,due to less humidity in the air to start with, it may still be a good idea not to blow on the evaporator as much still ( or unnecessarily ) but my guess is it would not affect things as much as in the summertime when it is both hot and humid out.

Good point about making sure everything's good and clean as far as the evaporator and condenser for maximum efficiency .... mine looks pretty good so far as I can tell except for a few bugs stuck in there since I drive so much at night.... I'll definitely have to check in between the radiator and the condenser because it's something I've not routinely done

While it's still hot out I may try pushing this project Along by ordering another Volkswagen fan speed controller and seeing what it looks like in the back for electrical hook-up purposes .... of course I'd also have to rig up some sort of holder for the speed controller.

Not being an electrical Guru my thinking is , when I plumb in the auxiliary switch , speed 4 on the auxiliary switch would mean the blower would run at normal speeds one through four and when i switch the auxiliary switch to anything lower than 4, that would effectively underdrive the speed?

I'm assuming there's nothing wrong with running an electric motor to slow?

I'm also hoping or assuming there's nothing wrong with blowing on the evaporator to slowly?

I'm hoping this project will show reasonable gains for very little ( basically just the cost of another switch and some wiring ) or no cost ( if I had a switch just laying around).
 

Andyinchville1

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Location
Virginia
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2003 Jetta TDI wagon, 5 sp, 226K miles
Might have issues with the evaporator freezing up without enough airflow over it.

Your gains if any will be almost immeasurable in my opinion.
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? ...

I've had drink vending machines freeze up before (even when inside a heated area) I used to snack and drink vend) but that was usually from a bad thermostat or ( per the refrigeration guy) a lack of or low refridgerant

I used to run a dehumidifier in the house basement and sometimes it would freeze the coils when it got cool outside(or inside as the case was in the basement). Of course, I am assuming the auto ac is a little better or smarter in being able to keep that from happening since the AC is also used in the winter to defrost etc ? or maybe the system somehow knows when ice is about to form due to system pressures / pressure differentials , or sensors etc that I may not even know about?

I guess doing it is one way to see but if a block of ice forms I hope nothing is too close to get damaged by the expanding ice .... I guess I could keep checking under the car to make sure it is still dripping water from the AC or is there a better way?

I'm going to try to order another fan switch after typing this .... so I can move on to (teaser) my clutched Power steering pump idea ;-0 (i'll start a new thread for that tho)

Andrew
 

compu_85

Gadget Guy
Joined
Sep 29, 2003
Location
Springfield VA
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... None :S
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.
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.

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
 

redbarron55

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Jul 10, 2010
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Navarre, FL.
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2012 Touareg TDI Executive
Just an observation on late model Jetta AC
1. The variable displacement compressors have had a problem with the RCV valve sticking and the AC seeming to have a delay in starting to cool or not cool at all due to the swash plate not moving.
2. The rubber flapper that closes off the radiator vent can become missing and fail to seal the shroud when the car is not moving fast enough to blow enough air through the AC hot radiator. The missing flapper allows the air to short circuit the radiators when the fan is exhausting the air from the shroud.
 

Andyinchville1

Veteran Member
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Apr 7, 2016
Location
Virginia
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2003 Jetta TDI wagon, 5 sp, 226K miles
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.

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
Hi

Good information ...about ac as well as the speed regulation of the blower motor

I ordered a switch alteady but I totally forgot about the resistors even though I replaced them before on my car.

I guess I'll have to buy another set of those and try to figure out how to wire it in in series to regulate the blower.

I feel relieved that the AC evaporator should not freeze up.... one less potential issue.

My thinking about not stalling the blower motor would be to start it up at a faster speed and then throttle it back ... maybe that's operating the motor like a poor man's capacitor-start .... start it off with a higher fan setting to get it spinning and then lower it down to operating range ...

Hopefully operating range with the potential for a speed one setting on the auxiliary switch in combo with the factory switch will not be so low as the motor refuses to turn (but I kind of sort of doubt that but I have nothing really to base it on other than actually just doing it).

Well , I guess here's to experimentation ! ....

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...
 

Michaelflat1

New member
Joined
Jul 17, 2021
Location
Colchester, United Kingdom
TDI
PD130 Seat ibiza
On 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
 

Andyinchville1

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Apr 7, 2016
Location
Virginia
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2003 Jetta TDI wagon, 5 sp, 226K miles
On 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
Hi

You know that is a very interesting thought and the modification seems simple ...almost seems like an every mod ... only for the AC system!

I'll start googling around to see if we have such a sensor in the EVAP that could be tricked using that resistor and / or potentiometer... I always wondered how everything was regulated I assumed maybe a pressure switch or something but maybe sensor there is how it is done.

Of course maybe another member here the chime in on that also in the meantime.

My guess is a variable potentiometer may be best because that way you could start off with a very cold evaporator to cool off the interior quickly and then dial up the potentiometer for it to maintain the coolness once you get it there using the minimum amount of evaporator coolness for max efficiency ( kind of like a heat pump only in reverse ...see below).

On the flip side , I'll throw out a comment that I remember my dad made one time concerning our homes heat pump heating system ( it's kind of a reverse analogy to air conditioning obviously but the thought or general premise may still apply ... only in reverse).

He complained that Heat pump heat felt drafty because it tends to come out not very warm when compared to regular resistive Heating or for that matter gas or oil heating if through air ducts.

The complaint that my dad had was the home while wormed to the appropriate temperature help drafty because the air blowing out of the heating ducts was not hot like "normal" heating systems. In his mind it didnt feel right despite the temperature being ok....

I'm wondering if we increase the temperature on the evaporator if we would not have a similar complaint or issue with the air conditioning system ....i.e. we may not feel that the system is working because we are blowing out warmer than normal air even though it's maintain the desired ultimate temperature? Maybe it won't "feel right"? .....

Admittedly, I don't think that would be the case because we do blend in heat to make the temperature feel good althought maybe during the initial cool down phase it is best done fast for maximum psychological / physical benefit .

I would definitely like to try the modification since it seemed so simple ( simply splicing into the sensor wiring add a potentiometer or resistor) seems a lot easier to do then adding a switch and resistors and worrying about how to mount all that stuff.

Of course maybe the ultimate combination is a system involving the two items ... a potentiometer resistor system to change the evaporator temperature and a motor control system to vary the airflow?

I do agree though that a lot of wind blowing around in a vehicle helps the perceived feeling of coolness....
I used to drive a step van for snack vending and that vehicle did not have an AC so a dash-mounted small fan blowing on you was a godsend when stopped at traffic lights excetera...

Hopefully we'll get more responses and replies to the idea of altering the evaporator temperature via resistors and / or potentiometers.

Thanks
 
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rocky raccoon

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Greater metropolitan Beaverdam
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2014 Jetta Sportwagen
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.
 

turbodieseldyke

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Jun 6, 2010
Location
Free Mustache Rides
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98 jetta
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...
You should add a Poll Question to the top:
[ ] I hope this guy doesn't set his car on fire
[ ] I hope this guy sets his car on fire
[ ] I think this guy's gonna set his car on fire, but I hope he doesn't, but I also hope he has a dashcam
 

GlowBugTDI

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2001 Beetle GLS TDI (BIODSL). Glow Bug TDI (sold)
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.
I really hope this is sarcasm😂. Because thats too good man!!🤣
 

rocky raccoon

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Greater metropolitan Beaverdam
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2014 Jetta Sportwagen
Not sarcasm. It be truth. The combination of glass panoramic sunroof and the screen-like headliner let a lot of sun-radiated heat into the car. The foil insulation panel blocks that and the ac does not have to work nearly as hard. It is easily pulled out during cold months if desired.
 

burpod

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cape cod, ma
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82 rabbit vnt ahu, 98 jetta vnt ahu, 05 parts car, 88 scirocco.. :/
well i do think this is kind of another silly thread, however... when i recently rebuilt my mk3 and installed AC from scratch, i did do something that i think would make it more efficient - the coolant fans only operate when the car is moving <40mph. this is adjustable by a VSS controlled switch.

i used a universal condenser that was approximately the same size as the factory one and had to make a couple custom lines (got some AC line crimpers, used a sanden compressor head adapter, had to slightly modify the compressor head - just enlarge one of the holes with a countersink drill bit with drill press :)). i have a flex-a-lite twin radiator fan and mk1-size radiator and good size fmic. my fan control is a simple relay with dual 87 outputs. radiator thermo-switch controlled low speed powers one fan through the switch. high temp/speed activates the relay to turn on both fans (which i an also manually turn on with a switch in case thermoswitch fails). when the AC is on and blower fan is on (and the pressure/temp switches allow), the "AC relay" powers the AC clutch and also triggers both fans to be on. however, the signal first goes through the VSS switch. so stuck in traffic or only driving very slow presumably not getting enough airflow - the fans are on. driving on the highway or at least 40+ i see no need to have the radiator fans on. so i think that would save a good bit of wasted electricity and reduce noise. if the 3rd speed temp switch (on the mk3, the 4 pin pressure switch) is activated, the fans will also go on, regardless of speed.

if anyone has any ideas on possible drawbacks to my system, let me know :)
 

Andyinchville1

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Apr 7, 2016
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Virginia
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2003 Jetta TDI wagon, 5 sp, 226K miles
In thinking about efficiency from the blower system standpoint

1) it was mentioned in an earlier post to use a pwm controller rather than resistors.... at first that sounded very complex and Technical but theb I Googled it and actually found some motor controllers using that technology available off of Amazon , prebuilt , ready to go ... just wired power and the motor to it and good to go!

How much more efficient energy-wise is that type of system versus resistors?

The controller's I've seen using that system are continuously variable so that's a great benefit no fixed steps as far as speed.

Does anybody have the specs on the blower motor as far as amperage or watts so i can order a controller big enough to handle the load?

Secondly, from an air conditioning efficiency standpoint ....

The cooler the outside air stays as it passes over the evaporator the less load there should be on the air conditioning system.

Has anybody noticed how the air coming out of our vents (when on vent ) is quite a bit warmer than the ambient temperature outside?

While I haven't had a chance to see the actual difference, I know it's quite a lot and if we could somehow keep the air from heating up as it passes through the ducting into thr passenger compartment i think that would be very beneficial...

As a matter of fact it was cool enough outside today to Simply open the windows and run without AC but if that same coolness could come through the vents you would not lose the aero on the highway.

Anyways has anybody experimented with insulating some of the ducting to see how that helps?

If I get a chance tomorrow I'll have to pop the hood and see if I can figure out how the air gets heated before it enters the passenger compartment

At some point I'd also like to take my laser pointer thermometer ( I think of it more as a Kitty toy then a useful instrument but actuality it is an instrument! ) to measure the difference in temperature between outside air temperature and vent air temperature in the cabin to see what the actual temperature rise is inside.

Maybe somebody here has already done that? What did you do to keep the temperature rise to a minimum?
 

Lightflyer1

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Round Rock, Texas
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2015 Beetle tdi dsg
Sounds like a blend door problem to me. If they are disintegrated (foam) they would cause this issue too. There are rubber plugs to fit in the holes in the blend doors after you clean the foam off available from a vendor on Ebay just for this application.
 

robertsonc

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Aug 3, 2021
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USA
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non
To save you need more items that will make your air conditioning system much more powerful. Plus not only powerful but also nadejde. I asked myself the same question, as did you. The solution I found is that you have to have a very good mechanism that will not have losses. I have perfected my air conditioning system by professional mechanics from https://www.airconservicing.org/type-of-aircon-service/. since then I do refueling very rarely, which saves me both time and money. Plus to all I have comfort that makes my life very beautiful and driving the car much more like a pleasure
 
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