air-con on - heater on - billy25
just come back from town,in my mates car, and he had the heater in "meltdown" mode. i noticed that he also had the air-con on as well, and asked him why? (i always thought air-con was to chill the car interior in summer). he said that its on all the time in winter,cos it dries the air,and helps stop the (damp)carpets and seats from going mouldy. can this be right?,or is he just wasting power by trying to heat and chill the car at the same time?.

air-con on - heater on - Altea Ego
Nope he is right. Ok it uses more fuel, but if you never use the aircon during the winter, the seals go, and when you need it next summmer it wont work. All the time in winter is a bit excessive, hot dry air is not that good for you all the time.
air-con on - heater on - Mark (RLBS)
I don't understand why the air would be dry. Surely the drying effect is a by-product of the condensation of the moisture from warm humid air onto a cold condensor.

That wouldn't apply in winter.
air-con on - heater on - Altea Ego
Dunno, but it DOES demist the windows faster than non airconned air
air-con on - heater on - No Do$h
Dunno, but it DOES demist the windows faster than non airconned

My car has a fast demist setting for winter use. Turns on electric pre-heat (diesel), rear-screen demister and aircon. As the pre-heat and engine warm, the fan speed increases to match. Only blows full when engine is warm, aircon is part of the process.
air-con on - heater on - Roger Jones
Words from the wise (not me) on A/C are basically "Use it or lose it". The larger the engine, the less noticeable and more negligible the impact on performance and economy. Look elsewhere on this site for HJ's advice on giving A/C systems a good blast from time to time. The cost of using it properly pales in comparison with repair costs if non-use causes it to fail.
air-con on - heater on - billy25
thanks R.F
it just didn't seem logical somehow! but then i thought he may have been pulling my leg a bit.(he's quite prone to that!)

cheers billy.
air-con on - heater on - Sooty Tailpipes
Well, it works exactly like a dehumidifier, and even if the car has electronic climate control (no manual A/C button) and you say set the cabin temperature to be 18?c, it will cool it down to that in summer and in winter when the ambient is less than 18?c, it will warm it up to that, but the A/C still cycles on and off, and the refridgerant pipes under the bonnet are still covered in condesation from the air.
air-con on - heater on - Aprilia
Air-con evap unit is 'upstream' of heater matrix; incoming air is therefore first cooled (and moisture condenses out) and then the air is heated to the desired temperature by the heater matrix

On my Nissan QX the air-con switches off if outside temp drops below 2 deg. or evap unit drops below 4 deg.

With air-con running the mpg seems to be at least 5% worse than without, so its taking a few horsepower. Mind you, it is incredibly powerful and in the hottest days this summer was able to cool the car right down to 'shivering' in about 5 mins.

Systems on Primera and Merc. C-class are bacially the same, although not as powerful and don't seem to hit mpg so hard.
air-con on - heater on - bertj
If you don't run the air-con frequently, especially in winter, you will eventually get the most horrible smells from the unit - think sweaty underpants! This is caused by bacteria (in the condenser, I think) growing in a nice soggy atmosphere. The smell is almost impossible to get rid of. You can buy aerosols which are supposed to work but they never did on an old Passat I had. Air conditioning means what it says - it dries the air as well as cooling it. The difference it makes to a fugged up car in the winter is incredible. If you've got air-con use it all the time and don't worry about the very small power/consumption penalty.
air-con on - heater on - runboy
The only problem comes when you turn the aircon off and, woof, up mists the windows!. I like to turn my aircon off a few minuted before home to dry off the pipes-helps keep the smell down.

Never keep a car long enough to test that theory though!.
air-con on - heater on - THe Growler
Always used 'em both at the same time during bitterly cold winter nights in Saudi, would warm the car up much faster.
air-con on - heater on - billy25
thanks for your veiws on this thread chaps! i'm nearly convinced that it seems the thing to i've done it, set temp to t-shirt weather..put on air -con!

slight smell at first, as some have mentioned, but this cleared after 5-mins.

trouble is...missus now thinks i'm trying to infect her with legionair's (had high profile in our local press last year....and she knows it was caused by an A/C unit on a public building)..can anyone suggest a decent face-mask for her to wear whilst in the car? (to put her mind at rest), she doesn't seem to appreciate my efforts with the paper bag with cut-out eye-holes i've supplied her with!!

air-con on - heater on - terryb

She has nothing to worry about. Legionnaire's disease is a water-vapour-borne disease, so unless she's breathing steam from your a/c cooling unit she's safe. Of course, if your car's a/c unit is steaming you've got other problems than legionnaire's!

air-con on - heater on - Mark (RLBS)
Its not the air con itself causing/carrying the disease, its the water that does the cooling. Different system entirely.
air-con on - heater on - Mark (RLBS)
sorry, didn't notice Terryb's reply.
air-con on - heater on - billy25
o.k chaps, the face mask bit was supposed to be taken as *tongue-in-cheek*, but i'll inform her that she's safe! when it's on anyway!

shame really.
i think i would have enjoyed her in a mask!(ooer...billy behave!!!) :-)
air-con on - heater on - terryb
Story of my life, Mark :o)

Value my car