Hi, why does the A/C come on in very cold weather?  1st thing in the morning, trying to defrost the car, I need maximum heat to the car and especially the windscreen. 

 

Currently I turn off the auto-heating and set heater controls to the windscreen manually.

 

Does anyone else have this experience?

 

Thanks. K

Because the a/c dries/ dehumidifies the air speeding up demisting.

The air conditioning does not actually attempt to cool the car at low temperatures IIRC due to issues with freezing the system and the passengers. Pressing the button for maximum demisting, with the temperature set at 22C or so,  is the correct method. Once the windows are clear then revert to auto. Hardly an 'experience' - just the way the demister/de-icer works.

It is also possible that the AC is actually a reverse-cycle system, Ie. both heating and cooling. Any AC engineers on here who can confirm this?

I think I can confidently say that an air conditioning system is not designed to run in reverse as a heat pump.

Is it just me or is the standard of questions getting rather weird?

Get Billy Goat Gruff on standby.

It is also possible that the AC is actually a reverse-cycle system, Ie. both heating and cooling. Any AC engineers on here who can confirm this?

 or not!

Hi, why does the A/C come on in very cold weather?  1st thing in the morning, trying to defrost the car, I need maximum heat to the car and especially the windscreen. 

 

Currently I turn off the auto-heating and set heater controls to the windscreen manually.

 

Does anyone else have this experience?

 

Thanks. K

aircon isnt just for making cold air  :dull:

aircon isnt just for making cold air  :dull:

 

Correct, Driving sometimes in cold damp nights I drive past endless cars with steamed up windows at the back. I have my A/C on, its lovely and warm inside and no steamed up windows.

 

With A/C the incoming air has the moisture removed by the A/C and is then passed over the heater matrix to be heated as usual.

Don't you have your A/C on all the time anyway? Or is that just me?!

For quick demist make sure the screen is clean. 

Press the "Max" demist button, top part of left-most control.

 

Auto is not as effective as manual control of "Hi", three fan bars and up and feet. That was only in -24, though, so your mileage may vary.

 

Clear the rear screen when it's that cold, the heater can't defrost the ice on the outside properly, and the Aux heater also won't help unless it's on for more than 30 minutes.

 

For a quick engine heatup: Aux heat on. Heat on LO. Fan off. 3k rpm. Should take around 2-3 minutes from 5C and you'll see the water temp jump rapidly. Then add heat with a few bars of fan and go out to scratch the windows..... I did this one today, the Aux had been on for 30 mins and I went out 5-10 min later. Water temp was back below 50, it took the 2-3 minutes to come up. 

 

A/C will also dry the interior air if it's running, but I'd be surprised if the compressor is actually functioning below around 5C. Running the compressor takes energy and therefore fuel, so if you don't need it, turn it off.

 

 - Bret

Don't you have your A/C on all the time anyway? Or is that just me?!

always on for me

Don't you have your A/C on all the time anyway? Or is that just me?!

Ever since I first got a vehicle with A/C its always been permanently on 24/7/365 - when it's hot it cools the air, when its cold it dries the air, so why would you ever turn A/C off?

The air conditioning does not actually attempt to cool the car at low temperatures IIRC due to issues with freezing the system and the passengers. Pressing the button for maximum demisting, with the temperature set at 22C or so,  is the correct method. Once the windows are clear then revert to auto. Hardly an 'experience' - just the way the demister/de-icer works.

So I am right to switch to manual heating in the early morning ?, before reverting to auto ?

Correct, Driving sometimes in cold damp nights I drive past endless cars with steamed up windows at the back. I have my A/C on, its lovely and warm inside and no steamed up windows.

With A/C the incoming air has the moisture removed by the A/C and is then passed over the heater matrix to be heated as usual.

But that's just Jose dogging by the roadside

Don't you have your A/C on all the time anyway? Or is that just me?!

Nope. It's not just you.

Been running my AC pretty much constantly for many years. Use It Or Lose it.

Clean and dry all the time - summer and winter.

Set to Auto with control on temperature with a bit of extra fan if fully loaded with people or really wet outside.

As above, have spotted lunatics running around with steamed up windows for no good reason.

Worst ones were local drivers when I worked abroad who thought AC meant "cold" for the expats and ran on recirculation most of the time. Crazy.

For quick demist make sure the screen is clean. 

Press the "Max" demist button, top part of left-most control.

 

Auto is not as effective as manual control of "Hi", three fan bars and up and feet. That was only in -24, though, so your mileage may vary.

 

Clear the rear screen when it's that cold, the heater can't defrost the ice on the outside properly, and the Aux heater also won't help unless it's on for more than 30 minutes.

 

For a quick engine heatup: Aux heat on. Heat on LO. Fan off. 3k rpm. Should take around 2-3 minutes from 5C and you'll see the water temp jump rapidly. Then add heat with a few bars of fan and go out to scratch the windows..... I did this one today, the Aux had been on for 30 mins and I went out 5-10 min later. Water temp was back below 50, it took the 2-3 minutes to come up. 

 

A/C will also dry the interior air if it's running, but I'd be surprised if the compressor is actually functioning below around 5C. Running the compressor takes energy and therefore fuel, so if you don't need it, turn it off.

 

 - Bret

Wow! I'm glad it's a lot easier in UK. A hot screen is a driver's best friend on a frosty morning. Get in and go in a few minutes.

Auto climate control!! Why fuss with it? Had climate for 16 years, I rarely touch it, may go down to 18 in a very hot summer otherwise its between 19 & 21 depending on the weather/time of year but generally just leave it to do its thing, no need to touch it imo - its always on AUTO! Ditto auto lights & wipers and now I've got a DSG I don't touch that either!! lol

.

Edited 6 January, 20179 yr by cherry evo

I never use any car scrapper to my windows, always let my TSI warm up for 2-3 minutes then I use the windscreen button to clear of the frost etc...Just press the front windscreen button on the left side of the temperature round dial/knob, air con should automatically be on & turn the fan speed to full, around 20-22c temperature.

 

Once cleared I then turn the fan speed down to 2-3 lights & drive for another 5 minutes or so, then switch to auto with auto & AC lit. 

 

Also use the air con all year round, air con is to condition the air around you (car) plus using the AC you will more likely have less problems with it in the future.

Edited 6 January, 20179 yr by BATVANVRS

Off will drop the used capacity of the compressor to around 2%, it won't turn it off completely. I figured as much, it's unusual to have one that turns off fully (as I have in the A2). I'll have to find an authoritative source for this one, the initial source seems pretty good. 

 

The air in the car has already been filtered - a/c on or off. a/c will dry it some - the effectiveness of which is partly dependent on temperature and humidity - but when you have near 100% humidity because it's raining, then each step is worthwhile. 

Running climate because you have it makes no sense if the compressor runs anyway.  Even without an air cooling component, the air will go through the pollen filter.

 

Key step to avoid trouble will be to regularly get the level of gas in the system proved and refilled if necessary, so every couple of years. Re-gassing is what. £50? A new compressor will be £1000...

 

 - Bret

Running climate because you have it makes no sense if the compressor runs anyway.  Even without an air cooling component, the air will go through the pollen filter.

But just going through the pollen filter won't decrease the moisture content of the air, that's why running climate all the time is worthwhile in a climate like the UK where the air is almost always moisture laden.

 

As I'm typing this there is thick fog outside...

Edited 7 January, 20179 yr by PetrolDave

Logically, if the compressor is running at 2%, you won't lose much humidity. I strongly suspect - i.e I'm sure I've seen but can't prove - that the humidity removed drops rapidly as outside humidity approaches 100% and temperature approaches zero, partly because the compressor is not working at full chat, but also because I'm sure there's some laws of thermodynamics in play here. Then the only answers are clean windows and fan speed. The clean windows thing? One side of the car, the rear window has been drawn on by a passenger. The other hasn't. Guess which mists over first? 

 

I frequently see ice on the inside of the rear windows at -10 or lower, simply because the air is humid in the car and that freezes on contact with the cold glass. I've also tried a couple of times to shift a thick bank of snow off the windscreen with an inside heater (2kW or so DEFA Termini). Doesn't work well - the snow isn't necessarily frozen to the screen any more but the heat triggers the inside humidity and it condenses back on the inside of the screen.  

 

 - Bret

Well, whats correct or not, I do not know.

But Ive noticed one thing, when having my dog in the back, the rear windows mist over considerable more with the aircon off, no matter the ambient temperatur. So it does make a difference, even well below freezing temps.

Interesting, maybe the 2% is enough to make the difference? I've not seen it. Might get the opportunity to check next week with extremely humid weather. 

 

Logically, it ought not to work. Doesn't mean it doesn't....

 

 - Bret

Edited 7 January, 20179 yr by brettikivi

Interesting, maybe the 2% is enough to make the difference? I've not seen it. Might get the opportunity to check next week with extremely humid weather.

Logically, it ought not to work. Doesn't mean it doesn't....

- Bret

Since when did logic apply to the real world? :p

I find that using the air con all the time means that residual moisture left on the evaporator makes the inside mist up straight away when I get in the car on a cold morning which means if you do you use it, you have to commit to using it all the time just to get rid of the moisture that the air con is providing. I hardly ever use my air con in winter and there is never any condensation on my windows unless I have a few passengers in.