My air con stinks !!!

[Alfashark]

On a Mk3 the AC compressor is permanently engaged - Even when you've hit the off button.  There's no clutched system, just permanent drive to the compressor. 

When you hit the off button, it simply turns the light off and reduces the compressor loading to about 2%, hence you won't have any effect on fuel economy unless you're in 30 degree heat and you're trying to get the cabin temp down to 18 degrees.

 

Just leave it on Auto and avoid all the issues that come with switching it "off".

[Hermit]

OK, I go with that Alfashark. 

 

With this car I have the AC on all the time until the weather gets hot, then I turn it off.

Sounds freaky but I just prefer to have the blower on and be a bit hot than have a big impact on the mpg.

Other days I'm happy for it just to be quietly 'conditioning' the air (humidity etc) at negligible cost.

 

Of course I don't know what impact it has on the mpg. I enjoy some spirited driving from time to time and don't fuss about mpg then so I'm not fixated on economy.

 

I know that winding down the window is fine as an alternative at low speeds but once over 45mph the drag from the open window will cause an even bigger impact on mpg. Its always a good idea to flush the car of very hot air when its been parked up by driving with windows down for a few minutes. Often the car's interior has got hot due to the suns radiation but the outside air is much cooler (30deg inside, 20deg out) so the climate control on auto will just crank up the fan speed to blow cooler air in and push the hot air out. 

 

I would like to know how much fuel the AC soaks up per degree of cooling for example. I've read 5-10% decrease in mpg but obviously depends on how much of a temp reduction you're trying to get. I like to have the facts!

 

[Fuel economy is an issue for me, both environmentally and financially (v.low income) so I pay for the fun times by driving carefully most of the time]

 

 

 

[Gerrycan]

The A/C system will have two separate matrix (radiator-like) through which the air passes, one will be a heater matrix deriving the heat from the vehicle's waste heat and the other will be a cooling matrix powered by the A/C system.

The climate control A/C system uses either matrix to control air temperature, or both to control the humidity as well as temperature.

 

My 3+ yo very base 1.4tsi mk3 Octavia estate as supplied in Australia only came with a basic (non-climate-controlled) A/C system, so I have to manually do what the climate control system ECU does to make things comfortable. Sounds a hassle but generally it is not an issue.

The Adelaide climate is generally hot (30 to 45 deg C) and dry (<50% humidity) in summer so I usually turn on the A/C only and use the fan speed to control the cabin temperature. This works well on a run and has minimal impact on fuel consumption usually less than 5mpg even when the temperature is in the high 30s.

The cooling matrix cannot run lower than about 4 deg Centigrade otherwise the moisture that accumulates on it would freeze and block it, so the A/C system only clicks in to maintain that matrix  4 deg temperature so even on my system the A/C is not fully engaged all the time. External air temp and fan speed determines how often and the intensity the A/C kicks in.

Officially the effect of running the A/C is around 0.5L/hour which equates to about 5mpg at legal speeds. Logically this means that the faster you are going the less relative effect A/C use will have on consumption.

 

However in town stop/start traffic the effects on consumption of running the A/C is far more. After all you are sitting there idling and the A/C is cutting in and out to maintain the 4 deg matrix temp then the radiator fan also kicks in (more electrical consumption) and idling consumption goes from 0.5L/hour to 0.8L/hour or more, doubling consumption for just sitting there. So I find in town that my consumption increases by about 8 to 10mpg on a hot day.

 

On one occasion a fairly unique set of circumstances (for South Australia) of 30 deg temperatures, very overcast conditions, and near 100% humidity meant I had to run the A/C and the heater and recycled air to try and control a comfortable cabin temperature and vapour build up on the inside AND outside of the windscreens on one long country run which knocked consumption by close to 8 mpg.

 

The UK climate is obviously very different, but based on my experience I can visualise situations where Climate control A/C will be 'fighting' itself to control humidity and say different zone temperature settings which might cause (more severe?) adverse effects on consumption.

[Alfashark]

4 hours ago, Hermit said:

OK, I go with that Alfashark. 

 

With this car I have the AC on all the time until the weather gets hot, then I turn it off.

Sounds freaky but I just prefer to have the blower on and be a bit hot than have a big impact on the mpg.

Other days I'm happy for it just to be quietly 'conditioning' the air (humidity etc) at negligible cost.

 

Of course I don't know what impact it has on the mpg. I enjoy some spirited driving from time to time and don't fuss about mpg then so I'm not fixated on economy.

 

I know that winding down the window is fine as an alternative at low speeds but once over 45mph the drag from the open window will cause an even bigger impact on mpg. Its always a good idea to flush the car of very hot air when its been parked up by driving with windows down for a few minutes. Often the car's interior has got hot due to the suns radiation but the outside air is much cooler (30deg inside, 20deg out) so the climate control on auto will just crank up the fan speed to blow cooler air in and push the hot air out. 

 

I would like to know how much fuel the AC soaks up per degree of cooling for example. I've read 5-10% decrease in mpg but obviously depends on how much of a temp reduction you're trying to get. I like to have the facts!

 

[Fuel economy is an issue for me, both environmentally and financially (v.low income) so I pay for the fun times by driving carefully most of the time]

 

 

 

 

If you have a scroll through the driving data screens on the MFD, there should be one called Consumer Convenience - Leave it on there and it'll tell you what's using juice and how much. 

 

Once the initial cool-down has taken place, for me it sits on about 200ml/hour during the day.  When I get up for work at 2am, the outside air temp is in single digits at this time of year and that display is showing 0 or as close to it as you can get for my 50km open road drive to work - I just leave it on auto and have the temp set to 24 degrees for the initial 5km or so and then dial it back to 22 degrees.

[Hermit]

Thanks Gerrycan. Thats very comprehensive.

 

You make the point that that the AC consumption is 0.5L/hr (time based) , not L/km. The extra load when bowling along the motorway will be a smaller proportion than when shuffling along in town. That makes a lot of sense.

 

Also you mention about recirculation. When there is very warm air outside and you have the AC on its an ideal time to switch to auto-recirculate so you don't push out the air you just spent a fortune cooling down. It would be good if that was automatically managed.

 

(Also just found your post from 3 Jan about Consumer Convenience)

 

Thanks Alfashark, I see the AC on the Consumer Convenience page but to be honest my eyesight isn't good enough to see exactly what its says. I didn't realise it was g/hr. I thought the display said AC was "1 in 8" or similar last time I looked which didn't mean anything to me. Over here in the UK we still use mpg for economy even though we have no idea how much a gallon of fuel costs as we've been buying in litres for decades now. Aren't we quaint.

 

I just found this page which looks helpful (and prev page) about fuel economy.  These graphs aren't in my Octavia manual (paper or online) yet the page1 illustration is OctIII pre f/l like mine:

https://www.manualslib.com/manual/948766/Skoda-Octavia.html?page=129

The point made on this page is how much less efficient the engine itself is in cold weather. I've very aware mpg is higher in warmer weather than when its cold but never been sure quite why.

[Gabbo]

1 hour ago, Hermit said:

Also you mention about recirculation. When there is very warm air outside and you have the AC on its an ideal time to switch to auto-recirculate so you don't push out the air you just spent a fortune cooling down. It would be good if that was automatically managed.

 

With automatic climate , heating, cooling, recirculation, fan speed, etc is all managed automatically by the climate system.

GerryCan was talking about his car which only has manual AC (I dont think that option is available in Europe).

[Hermit]

Well, if the climate control automatically switches to recirculation when the AC is working hard I'm impressed. Thing is I'd probably never know when it was doing it... or how much. I'm an old fashioned control freak - I probably need to learn to let go and trust the car knows best. I trust in the DSG to do a good job selecting gears so I'm learning to let go.

 

Maybe one day the acceleration/deceleration will also be automated and we'll just sit there and with voice control say "a little faster" and the car will make all the judgements.

Hhhmmmm..... Sounds very boring.

[Hermit]

Oh - and I've just been out in the car and I can see now the 'consumer convenience' display shows the consumption along a bar with 1/8 gal/hr in the middle. Even with the heated seats both on it hardly makes any mark on the left (0) end of the scale. It never seems to show anything which just goes to show I don't need to worry.

The weather is cool again so concerns about AC have faded till the sun comes out again.

[Gerrycan]

4 hours ago, Hermit said:

The weather is cool again so concerns about AC have faded till the sun comes out again.

Or if it rains, when you and others get back in the car dripping wet and the internal windows fog up, then the climate control A/C (assuming it is on) will use both the cooling and heating matrix, might even switch to recycling mode and direct to the front window ports automatically. As Gabbo said, my A/C is manual so I'm not sure to the extent the Octavia climate control operates although I know the climate control system in a Subaru Outback does do all that adjustment automatically.

It is also quite probable that A/C in general has less effect on your diesel consumption than it would on a petrol engine which is more sensitive to adverse influences (particularly noticeable if towing, or strong headwinds or going up hills).

Edited 23 April, 2018 by Gerrycan

[Hermit]

The Octy is so dam clever I can't tell when it's being clever. 

 

Like I said, as a driver I think I'll be out of a job soon enough. We'll end up sat around on our playstations reliving the fun of 'yesteryear'.

[Rodge]

On 22/04/2018 at 22:17, Alfashark said:

When you hit the off button, it simply turns the light off and reduces the compressor loading to about 2%

This will reduce fuel consumption.

 

With the automatic system you have to rely on the humidity sensor to detect if you're soaking wet and appropriately adjust the air conditioning for maximum drying.

[spinifex]

Getting back to the original question - my car has done this several times now too.

I have a Mk3, with climate control.  This is on almost 90% of the time, in auto, and i force-recirc the air, as the auto/climate-control doesn't seem to do this.

 

Any time i have the AC turned off - usually because I drive a lot with the windows down - I always ALWAYS have the fan blower still running.  I NEVER turn the fan off.

So why does my AC get that rotten cheese smell, when I turn the AC back on again?

There is no reason why my condenser/evaporator, or the pipework or vents, or any other part of the climate control system, should have built-up bacteria or moisture in it, as I know you are supposed to run the fan for a good few minutes after turning off the AC... which as mentioned above, my fan is ALWAYS running.

Can anyone explain why I continually have the mouldy cheese smell for a good few minutes after first turning the AC back on again?

I'm not happy to have to change the damned pollen filter & run a smelly-bomb through the system every couple of months, as there's clearly either a design-fault, or user-error issue occurring here.

[SoupDragon]

Try NOT using the re circulation. The auto setting does use the re circulation when necessary, eg when you use the windscreen wash and when it is particularly dusty outside. Otherwise, don't use the re circulation.  Is it very dusty where you live? Perhaps you can get or make an upgraded pollen filter and use the outside air.

[Gerrycan]

Spinifex lives in Brisbane Queensland which is sub-tropical and gets a fair bit of humidity and rain so it is not unreasonable to run on recirculated air a fair bit.

I'm only guessing here but I would think it would take quite a bit more than a few minutes of running outside air through the cold air matrix (with A/C off) to warm it up to outside ambient temp AND dry it off.

The other thing maybe worth checking is that the drainage point for the A/C is completely free and not (partially) blocked with whatever and allowing some of the condensate to collect and allowing 'things' to grow.

Speaking of which I must spray my mushroom farm I bought from Aldi.  

 

[spinifex]

Thanks Gerrycan>

When I run the fan-only, it's usually because I've go the AC off, and the windows down, and it's usually a good 30min drive or more.  That's why I can't understand why the "internal bits" can't dry off sufficiently.

I did bring this up at a previous service, and they told me it was because the pollen filter was dirty.... and charged me an exorbitant amount to replace it and put a bomb through the car/vent system.
I asked for the pollen filter when I collected the car, and TBH, it looks pretty average to me... certainly not what I would call blocked or clogged..... not even really discoloured at all.

I must admit, it smelled pristine after that for several months, but it's come back again after another several months of using the air on and off.. but as mentioned, fan ALWAYS running permanently.

I'll try your suggestion and try to locate the AC drain to ensure it's not blocked.  Can't see how it could be, on an 18mth old car, but I didn't think my oil-cooler was going to break and leak oil into the radiator coolant after only 3weeks of ownership either !!!

[Noz]

I've had this is a few cars. Defo worse if you don't use the AC all the time but my last car had it even though I did.

Bacteria gets into the system. Not sure where it's living exactly. I got some AC spray and found the air inlet and sprayed it in with the AC on full blast. Had to do it a few times a year but it works.

 

Bizarrely I tracked my problem down to sneezing, believe it or not. I had a minor sinus infection and every now and again I would do a sneeze that smelled rank and I noticed it was exactly the same smell as the AC so I reasoned it might be the same bacteria. Got it treated and problem solved. So I'd been reinfecting my AC system repeatedly.