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

Andyinchville1

Veteran Member
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Location
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2003 Jetta TDI wagon, 5 sp, 226K miles
Hi All,

1) Since summer is here and my MPG have taken a hit because of AC usage I was thinking of something that I think could help us get back some MPG's maybe....

Back Ground:

The other day while I was driving at night, I had the fan at speed 1 and it was getting a little chilly in the car so I shut off the AC and ran vent for a bit .... eventually it got too warm and due to the humidity "sticky" inside so I turned the ac back on.

This happened for several cycles ( I was thinking the later at night it got maybe I could just run vents because coolness would set in but that point never came).

I remember reading in an AC thread here that it takes about 15 minutes for the AC system to stabilize and become more efficient , so my turning the system on and off was probably not ideal.

With that I decided to run the AC at fan speed 1 and blend in a little heat ..... NOW it was comfortable.

Problem :

From an efficiency standpoint , it is kinda crazy running the AC and mixing in heat to make it comfortable ... afterall the engine still has to spend energy to turn the compressor to make things nice and cool for the AC system!

Potential Solution :

Anyways , it got me to thinking ....

IF the fan speed could be reduced somewhat then the cabin would (or could) be made more comfortable WITHOUT the addition of heat and WITHOUT having to run the compressor more .... (i.e. the fan blowing fast on the evaporator makes the compressor work more to maintain the cold temp on the evaporator BUT if we slow the fan speed , the evaporator does not lose its coolness as fast and the engine driven compressor doesn't have to work as much therefore reducing MPG losses.

My plan to achieve this was to wire in an ADDITIONAL fan speed controller in series with the existing one so the fan speed could be lower and have more steps (speed wise) in between.

What are your thoughts on this ? (is running a fan too slow bad for the fan ? Is maybe not blowing on the evaporator enough bad for the AC system?) maybe I overlooked something?

2) As a second way to help with Air Conditioning efficiency (and I read it here in another post but it was so long and technical I could not get the bottom line on it)

What Freon (like R12 , R 12a, R415 ? others ?) could be used INSTEAD of our R134A to make the AC system more efficient ? I know there may be issues with seals BUT they could be replaced I guess ..... Just seeing which freon was the solution and how much it could save MPG wise.

3) I suppose if one had an unlimited supply of mineral free / distilled / rain water one could rig a mister in front of the AC condenser and maybe that would help?

Anyways, thanks in advance for any and all help on this ... Also, any other ideas on how to save MPG's WITH the AC running ?

Andrew
 
Last edited:

IndigoBlueWagon

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I can't see I've ever seen any measurable drop in FE from running the A/C. Maybe there is on short trips when you're cooling the car down, but on long drives with or without the A/C FE seems to be the same.

I'd try two things when it gets colder. Aim the vents up so they don't blow on your face, change the direction of flow to the combination of floor and vents, or, if those don't help, turn up the heater control to blow less cold, but still dehumidified, air. And drive more, worry less about the FE. I don't think it's hurting you as much as you think.
 

Mongler98

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he
You need a hobby. Or maybe a Prius.
has a VW he wants to make better than millions of $ R&D and testing have already basically perfected vs cost.
some people just think they can out smart billions of $ in engineering history.
oh right... a hobby... sounds right lol
 

ToxicDoc

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2001 Jetta, S7, .216
As you mention, the decisions are vs cost (also regulatory considerations). We routinely use different injectors, turbos, computer programming, clutches, shocks, etc to get better performance from the factory. Why is the AC system excluded? To play devil's advocate, R-12 would be more efficient, but the system is not calibrated for it.
 

holeintheice

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2015 Passat
Will rob 10-40 HP to run compressor. And no does not take 15 minutes to "Stabilize". It takes one minute for pressures to equalize when **** off. Depending if stopped or cruising. Stop watching back yard mechanics on YouTube.
 

Mongler98

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Will rob 10-40 HP to run compressor. And no does not take 15 minutes to "Stabilize". It takes one minute for pressures to equalize when **** off. Depending if stopped or cruising. Stop watching back yard mechanics on YouTube.
robbing HP is not a very good way to look at it. only if you are WOT or towing and need every HP. stock is what 110 usually use about 20 to 30 for monral driving, AC DOES NOT ROB HP it can hinder a little on MPG but not take away from daily power. if it is that big of a deal for you then you need to SLOW DOWN or reconsider your driving needs.
 

oilhammer

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outside St Louis (where it's safe)
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There are just too many to list....
This is such a dumb topic.... but I can't help myself, because there is so much misinformed people on the topic.

The compressor load is VARIABLE, depending on the heat transfer load from the cabin. Some cars have more variation in their ability to ramp the load up or down, but in any event, once the bulk of the heat load has been removed from the cabin, the compressor load is not as great. And yes, this CAN take 15 minutes, it just depends on how hot the car's cabin is, how hot the outside temp is, and how cool you want it to be, as well as how well you understand how the recirculate works. Lots of people don't... they try and cool a 130F interior by recirculating the air, when the outside temp is a comparatively cool 100F.... that is dumb. You should NOT use the recirculate option for that. Push the superheated air out, then the system need only start from 100 instead of 130.

And as far as "robbing power", the ECU can over ride any A/C command if a certain level of engine output is requested (via your right foot). So it makes no difference, if you NEED all the engine's output, the A/C will be costing you 0 hp anyway. It will be switched off.

TDIs are wonderful engines for NOT being hit hard with A/C. No other 4 cyl or even some larger engines are as easily able to deal with this extra load. Even many VAG gasoline engines in an otherwise identical car (with identical A/C systems and identical heat loads) will feel like your threw a boat anchor out when you press the A/C button at first. And so many cars need the A/C switched off due to extra load demand of the engine so often when driving that you can actually FEEL the cooling drop in and out. TDIs don't do that. You can run 100 MPH up hill on a highway and the A/C will happily keep you cool. Try that in a 4 cyl Camry and by the time you get to the top of the hill you'll be sweating.

Part of the word "efficiency" is best displayed just as the TDI left the factory. It is already hyper-efficient, especially when it comes to dealing with the extra load of A/C.

Like so many of the OP's entertaining " ////////// ligasiudiausgpxueqbbhbaklbjb ////////" threads, this is another that has no good merit. Sorry.
 

IndigoBlueWagon

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Well, I learned one thing. I rarely use recirc, but did yesterday to cool down my pretty hot interior. Now I know I shouldn't have.
 

Andyinchville1

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2003 Jetta TDI wagon, 5 sp, 226K miles
Interesting about the Recirculation .... I typically don't use that figuring some fresh air is better than just recirculating the air inside (of course when covid first hit I did buy a HEPA filter for the cabin air filter).

On hot days, while I'm loading the car (or when doing the first run of the day ( I do courier work) I typically open the doors to let out all the hot air and by the time I am ready to roll , it is pretty much ambient temp inside the car before I start up.

One thing that did just pop into my head that I have never heard of anybody doing as far as AC Mods is concerned is actually adding to (or installing) a larger condenser ..... that would seem to help reduce the work the compressor needs to do if there is more cooling area to passively remove heat? (almost like a FMIC VS a SMIC but for AC). Could that possibly help AC efficiency and MPG?

I know R12 is hard to come by (maybe even extinct ? I'd have to research) but how many more MPG's could one get using a non R134A under the same conditions? (even if seal change out is needed ... knock on wood I have never had an issue with my AC).

When I turn the AC on my car does feel it and my MPGs reflect it .... maybe some cars feed in more fuel to make it feel like less of a drag than it really is ? .... in any event my MPGs do go down a fair amount with the AC on.

Since I drive alot for work (I was averaging about 300 miles a day for a long while), efficiency and MPGs are kind of my fun distraction.... I know it does not necessarily save a lot of $$ getting a few more MPG's BUT ....

I would love to be able to get 60 MPG at 60 MPH but the best tanks back to back I have ever gotten were only 56 mpg ( I don't hypermile (no drafting, no pulse / glide , no engine off at lights , no running without AC on hot days etc...) I try driving "normally" (although friends think driving 62 to 65 MPH is hypermilling! .... I used to drive the same route all the time but now mostly a mish mash of long drives so its hard to accurately see immediate changes .... just changes over a long period of time).
 

ticaf

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how hot is it outside ??
On my mk7, it's hard to be too cold inside on speed setting 1, particularly on a hot day. so consider yourself lucky your AC is working that well.
 

ezshift5

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2013 JSW TDI (Enroute BB).......2017 Jetta 1.4 turbo 5M ....................
A thoroughly enjoyable thread - with surprise OH humor ................and engineering observations.

My buyback 2 liter JSW TDI 6M showed little MPG/power loss with a/c use.

OTOH, the little 1.4 turbo 5M replacement takes a big time MPG hit - 85 cubic inches is a small (motorcycle sized) motor.

Again, great thread!


ez
 

Mozambiquer

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1998 VW Jetta TDI. 1982 VW Rabbit pickup, 2001 VW Jetta TDI
I think this thread is humourous, but has some merit. Hypermiling is fun, and I used to do it as a hobby as well. My best tank was 56mpg in my 1982 rabbit pickup with a 4 speed. I didn't have AC, so never had to worry about that.
Now I tend to not make enough time to hypermile, and so I go faster. Yeah, I don't get as good economy, but I get there a few minutes faster.
On the subject of AC, one thing I've heard mentioned is red Tek 12a refrigerant. I guess it's supposed to run a lot lower pressures and so would rob less power. https://redtek.com/12a/
I doubt that it would make a notable difference in fuel economy, but it could.
I have observed that in my b5.5 Passat, driving on the highway I do get about a 1-2mpg drop running the AC, with a wife and baby though, I don't try to run without unless it's nice outside.
 

IndigoBlueWagon

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One thing I really appreciate about the MKIV Jetta Wagon is if you crack the driver's and left rear passenger windows equal amounts you get a lot of air through the car and very little noise or buffeting. I've run for hours at high speed with those windows open an inch or so and it can help you not use A/C.

Then of course there are days like today where it's only about 70 out but it's raining and the humidity is past 100%. A/C even though it's not hot.
 

kbeefy

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ALH
Changing the refrigerant out to gain a miniscule amount of mileage increase would cost alot more than it would benefit.
There is alot more to an AC system than just what refrigerant is in it.

Different refrigerant requires different oil. The system should be flushed, components drained and after assembly the correct (or alternative) oil added.
Older systems use a different design condenser. Not sure how it would perform on a more modern one, maybe fine.
Seals should be replaced, not a big deal if it's disassembled anyways for cleaning.
Orfice tube/Expansion valve would need to be changed for one appropriate to the refrigerant.
Pressure switches should be changed to ones appropriate to the refrigerant.

Unless you have a recovery machine, you would need to pay someone to evacuate the system.
Then theres the cost of and availability of the actual refrigerant. If considering R12 it is no longer commercially available in the US, and hasn't been for some time. I have seen it for $10/#, and I have seen people not able to find any for $100/#.
 

Mongler98

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#1 best hyper mpg trick is to tape up all the seams on your car.
Cheaper than a few cans of 12a and ac tools.
 

oilhammer

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outside St Louis (where it's safe)
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There are just too many to list....
Things got tweaked (decades ago) to make up for any efficiency loss in the refrigerant change (and that is changing again, FYI). They all work to get the coldest point in the system as cold as it can get but not be at the freezing point of water. Nothing is different in that respect.

I forget what the exact change in efficiency was (been a long time since I was in that textbook) but it was not that much, and was easily overcome by a couple simple changes like running a slightly higher high side pressure to initiate a slightly greater pressure drop at the restriction point in the system, and with a better heat exchange on both ends (evaporator and condenser) but mainly the condenser.

I can tell you that over the years, I have converted countless cars from R12 to R134a, and most of them, especially those with a more efficient expansion valve system instead of a fixed orifice tube (non-dynamic) system, had no ill effects and no real loss of heat exchange potential. My '91 Jetta went longer on R134a than it did on R12, and it would still be capable of giving you an ice cream headache on a 100F day.

The change was for environmental reasons, nothing more. And that same reason is what has prompted the change once again... this time to R1234yf.

"Anything" can be a refrigerant, so long as it can be compressed and forced through some sort of restriction. Good ol' Earth air (78% Nitrogen, 21% Oxygen, ~1% Carbon Dioxide and other trace elements) can be used.... but it would take a LOT of energy, a LOT of compressor(s) with massive surface areas for heat exchange. It would be terribly inefficient. But it would take away heat. Ever take a valve core out of a tire stem and deflate the tire? You'll actually see a film of frost form on the end of the valve stem as the air is escaping. Even if the air inside the tire was warmer than the outside air.
 

Mongler98

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98 Jetta TDI AHU 1.9L (944 TDI swap in progress)
Things got tweaked (decades ago) to make up for any efficiency loss in the refrigerant change (and that is changing again, FYI). They all work to get the coldest point in the system as cold as it can get but not be at the freezing point of water. Nothing is different in that respect.

I forget what the exact change in efficiency was (been a long time since I was in that textbook) but it was not that much, and was easily overcome by a couple simple changes like running a slightly higher high side pressure to initiate a slightly greater pressure drop at the restriction point in the system, and with a better heat exchange on both ends (evaporator and condenser) but mainly the condenser.

I can tell you that over the years, I have converted countless cars from R12 to R134a, and most of them, especially those with a more efficient expansion valve system instead of a fixed orifice tube (non-dynamic) system, had no ill effects and no real loss of heat exchange potential. My '91 Jetta went longer on R134a than it did on R12, and it would still be capable of giving you an ice cream headache on a 100F day.

The change was for environmental reasons, nothing more. And that same reason is what has prompted the change once again... this time to R1234yf.

"Anything" can be a refrigerant, so long as it can be compressed and forced through some sort of restriction. Good ol' Earth air (78% Nitrogen, 21% Oxygen, ~1% Carbon Dioxide and other trace elements) can be used.... but it would take a LOT of energy, a LOT of compressor(s) with massive surface areas for heat exchange. It would be terribly inefficient. But it would take away heat. Ever take a valve core out of a tire stem and deflate the tire? You'll actually see a film of frost form on the end of the valve stem as the air is escaping. Even if the air inside the tire was warmer than the outside air.
my air compressor IS a refrigerant system when i dump the tank (80gallons) out of the .5" drain pipe. INSTANT ICE (about 1/4" tick over 12 feet of 1/2" copper
does not last long LOL
 

ezshift5

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2013 JSW TDI (Enroute BB).......2017 Jetta 1.4 turbo 5M ....................
Again, great (entertaining AND informative) thread.

For Mozam: My 1982 VW Rabbit Diesel had a 5M - but I never calc'd 56 MPG. Came close - IIRC 53 or so. At 300,000 I sold it to a VW restoration guy. He said he got twelve grand after paint, other cosmetics et al........(later his son said "No way: he was screwing with you)"

The '13 JSW TDI 6M wagon replaced the pickup (no more hauling a bed full of bark)

Next time I'm in St Louis I may have to offer OH a drink - - - for his pithy sense of humor/style.

It's all good!


ez
 

Andyinchville1

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2003 Jetta TDI wagon, 5 sp, 226K miles
how hot is it outside ??
On my mk7, it's hard to be too cold inside on speed setting 1, particularly on a hot day. so consider yourself lucky your AC is working that well.
HI,

Outside temps are mostly about 85 to 95 degrees when I drive so not too crazy hot ( I typically drive later in the day (usually after about 7 PM)

I don't know if my AC is any better than normal since it is just a working stock system.

My car does have Ceramic heat rejecting window tint all round though except the bottom say 80% of the windshield ( I was thinking of having the rest of the windshield done in clear thermal blocking film tho .... not technically tint since it would be clear).

Andrew
 

Rob Mayercik

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2002 Jetta GLS, Baltic Green/Beige
If you're looking ways to "improve" the AC, what about a PWM circuit and variable potentiometer to replace the fan resistor pack and discrete speed switch? Then you'd get finer control over your blower to play with...
 

Andyinchville1

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2003 Jetta TDI wagon, 5 sp, 226K miles
If you're looking ways to "improve" the AC, what about a PWM circuit and variable potentiometer to replace the fan resistor pack and discrete speed switch? Then you'd get finer control over your blower to play with...
HI,

Yes, I would love to have the ability to slow the fan down below speed one without damaging anything .... I was thinking simply wiring another fan switch in series but your solution is probably much better (altho admittedly sounding above my head in complexity).

Would you mind going into greater detail how your system works and what needs to be bought?

Thanks

Andrew
 

Lightflyer1

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Round Rock, Texas
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2015 Beetle tdi dsg
You really think slowing the AC blower fan down slower than the low setting is going to save you "ANYTHING"? Open the windows and vent the hot interior. Turn the fan on low and recirculate and the temp as warm as you are comfortable with. The blower will use little power and the AC will cycle on and off as needed instead of running full blast all the time like here in Texas summers. In a properly operating system that is about all you can do short of shutting it off and using the windows, if you want to save anything.
 

Rob Mayercik

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HI,

Yes, I would love to have the ability to slow the fan down below speed one without damaging anything .... I was thinking simply wiring another fan switch in series but your solution is probably much better (altho admittedly sounding above my head in complexity).

Would you mind going into greater detail how your system works and what needs to be bought?

Thanks

Andrew
It's not something I have, it's just an idea I had while reading your post.

The automatic climate systems on higher-end cars must have something along these lines, as they tend to have a lot more fan speeds than our simple 4, though I will concede the resistor pack is far cheaper/simpler/more reliable than a pulse-width modulation setup.
 

oilhammer

Certified Volkswagen Nut & Vendor
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Location
outside St Louis (where it's safe)
TDI
There are just too many to list....
Even a lot of fixed multispeed blowers have PWM controllers, they just don't use all the possible variations. Same for cooling fans. They do not use the old fashioned bank of resistors and relays. Lots of stuff is like that, actually. The *could* infinitely vary things, but they don't, because there is no good reason to, so that portion of code is simply not in the software.

Like an electric EGR valve that has "0%, 25%, 50%, and 100%" operating conditions... yet there is only two wires (fixed 12v positive, and modulated ground from the ECU) that actually work it. Sure, it could be open at 73%, it has the capability, but evidently the EGR's job is adequately performed with only 25% and 50% variables besides FULL on or FULL off.

Now we have variable speed controlled motors for things like electric fuel pumps, window lift motors, wiper motors, parking brake motors, etc.
 

TurboABA

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2010 Jetta 6spd MT, 2014 Touareg Execline
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.....
 

Andyinchville1

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Virginia
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2003 Jetta TDI wagon, 5 sp, 226K miles
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.....
HI

As far as wheels , I started off with factory steelies and then lightened up with Factory Avus rims ....

I have even lighter Volk TE 37 wheels but cheaped out and instead of buying 4 wheels from the buyer I got his other set of 3 wheels figuring I could buy the 4th more reasonably priced than he was asking BUT turns out the 4th wheel is really hard to come by and I may have to end up ordering new and waiting several months for it to get made and shipped.

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
 
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