"Forcing" aircon to activate in cold weather

I'm paying for being a cheapskate now and not opting for full climatronic control in my VW Touran.

What hadn't occured to me was that despite having aircon, there would be no way to force the aircon to activate for demisting purposed in cold weather. I've never had (or driven) a car where this wasn't possible before and I'm sorely missing it in this cold damp weather.

Presuming that the compressor is electrically activated somehow, how hard would it be to wire an "overide" switch to enable to activate it when *I* want?

Could it be as simple as wiring up a supplimentary12v feed to compressor or is that *way* to simple?

Tim

Reply to
Tim Downie
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I seriously suspect that you have never had a car where this is possible. More likely the way the indicator light is wired up. On Golf IV the light came on to indicate that the switch was on and there was power but the compressor clutch wasn't activated unless gas pressure and outside temperature sensors were happy.

Climatronic control still doesn't activate the compressor below 4 decrees C either.

Reply to
Richard Polhill

Well in my car it the A/C won't come on below 6C, but that is engine bay temperature, not outside temp.

Reply to
Mark Hewitt

Oh yes I have. You *know* when the aircon is working by the almost magical way the windows demist when its working. Compared to my old Citroen (with full climate control), my VW is utter pants when it comes to demisting.

I can't vouch that any car I've driven has allowed the aircon to work at that temperature but it sure as heck has worked at higher temps.

Tim

Reply to
Tim Downie

In cold damp weather there's a very real possibility of the moisture simply freezing on the heat exchanger. Which is why most don't work below a certain ambient temperature.

Reply to
Dave Plowman (News)

Am I hugely missing the point here? Can't you just press the A/C button...? Mine works whatever the weather?

Reply to
Iridium

'fraid so.

Nope. There is no A/C button to press. I can turn the A/C off in "economy mode" but it's clearly not working for demisting purposes just now.

Wish mine did. :-(

Tim

Reply to
Tim Downie

True, but that'll take a little time and in that time, it'll have sucked out a heck of a lot of moisture out of the air.

Obviously I wouldn't leave it running at this time of year but I would like the option of running it when *I* want to run it.

Tim

Reply to
Tim Downie

Does it? What car is it? How do you know it works? I mean if the temperature outside - the incoming air - is below 5 degrees how can you tell the aircon is trying to chill it?

The fact is, there is no real benefit to using aircon to attempt to chill-dry air if the air is already chilled to below 5 degrees. The air is already as dry as the aircon can get it by dint of being as cold as the aircon can get it.

Aircon works for demisting at higher temperatures as it condenses the moisture carried on in warmer air. If the air is already too cold to carry too much water vapour, there isn't any in it to dry out using the aircon. Ergo it is designed not to come on unnecessarily.

Reply to
Richard Polhill

Whether it comes on unecessarily or not and at what temperaure is not the issue here. The issue is that in cool (not necessarily cold) weather, I cannot activate my aircon for demisting purposes like I could in my old car when I need to for demisting purposes, something it is invaluable for.

Tim

Reply to
Tim Downie

And I still don't believe you could in your old car, nor that you'd get any benefit from doing so. I actually always believed that it made a difference in my old '99 Bora, and was frustrated with my '02 Alfa 147 with climate because it never let me turn on the aircon the way I could with the Bora. Two cars later I bought another '99 Bora and discovered, whilst researching a faulty aircon, that actually it doesn't come on below 5 degrees. Any benefit was imagined, triggered by the presence of a little glowing yellow light. Compressor still wasn't turning.

If you feel you *must* have it working, overriding the manufacturer's design decision, the trick is to fool the temperature sensor input into thinking the temp is high enough. Now this depends on whether the system is simple and uses a thermostat switch which you can simply short, or whether it is computer controlled and takes an input from the outside temperature monitor

Reply to
Richard Polhill

What makes you think that? Genuinely, I think you might be just believeing a little yellow light means that the compressor is turning.

Cold air below 5 degrees isn't going to be noticably chilled by aircon, it is not going to affect the already low levels of water vapour in the air and therefore is not going to affect the demisting ability.

Reply to
Richard Polhill

2004 206 XSi, turn it on and the windows clear quicker - that and the light comes on, and if you're idling you see the revs increase slightly and hear it click.
Reply to
Iridium

See my other reply. And the light is green :-)

Reply to
Iridium

Thankfully, I'm not interested in what you *believe*. I *know* that activating the aircon in a cold misted up car dramatically improves demisting.

Well that at least is a potentially useful suggestion. All I need to do now is work out where it receives its inputs from. Chances are it's some stupidly complicated digital system though. :-(

Tim

Reply to
Tim Downie

So you performed a side by side comparison?

How cold? Over 5 degrees yes it will. At 1 degree, no it won't. Air that cold is already dry, putting it through another chiller will make it no drier.

Now if you have the thing demisting and then think, after a few minutes, to turn the aircon switch on, then how can you say that any demisting effect afterwards would have been different without the little green light?

My point is that the manufacturers have it disbled at low temperatures for good reason and you probably don't want to mess around with it.

Reply to
Richard Polhill

Well, if it blew warm air onto the windows and recirculated the air through a dehumidifier then a heater, I can see that working. But where would it get the heat from?

Andrew

Reply to
Andrew Morton

FFS! Who introduced this f*cking 5 degree crap? It certainly wasn't me. If you want to argue the toss about temperatures below 5, fine. I don't give a monkey's however. All I want to do is turn my aircon on in cold weather when my car is misted up. Is that so hard to understand?

Would you like to come round and look at my condensation? Does your car suffer with any condensation at this time of year? Can you turn your air con on for demisting purposes? On my last car I could. On this one I can't. Got it now?

Tim

Reply to
Tim Downie

Have you actually owned a car with air con?

Tim

Reply to
Tim Downie

Yes but VAG will have thought about this...

...surely?

It strikes me as being very strange. Everything I've driven has either had an ECON button, an ON / OFF button or it's run the compressor when manually put into windscreen mode.

As much as VW badged stuff annoys me I *cannot* believe that you do not have the option to turn on or off the air conditioning compressor. Is this the semi-automatic system you have?

If you force the system to run at too low a temperature you'll freeze the air conditioning system. That will FUBAR the air conditioning system. Freezing bad news. :)

Don't do it. Chances are you'll bugger it up.

What ambient air temperatures are you trying to run the system in? Do you park in a garage? What's your typical trip? Is the car just generally damp? If you are running in mild (high single digit) temperatures, you don't park in a garage and your usual commute or drive is inside ten miles, the system is probably retaining moisture. A longer drive with the heater at full will dry the system out. By longer, I mean, forty minutes plus. Wear shorts and a t-shirt, it'll be uncomfortable... but it should help demisting performance the next day.

Also, invest in some crystal kitty litter. This is silica, it absorbs moisture and works a treat. I use old peanut butter plastic containers with holes punched in the lid and an old sock to keep the litter in place.

Finally, what does the handbook say about demisting in cool weather? It ought to at least provide some clues?

Reply to
DervMan

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