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Car Air Conditioning.

Dave Plowman (News) expressed precisely :

I don't do traffic jams :-)

Reply to
Harry Bloomfield
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Understood, thanks.

Reply to
Bod

But if the car is misted up, chances are the ambient air is full of moisture too.

Remember a few people piling into a car on a summer's day after a sudden shower. The AC was on in the car and it was cool. The windows misted up instantly. Never did quite work that one out. ;-)

Reply to
Dave Plowman (News)

(Ignoring the 205's footwell swimming pools) Yes, but passing it over the evaporator will pull the moisture out.

Recirc?

Reply to
Adrian

Right. But thought we had moved on to discussing clearing a misted screen with no AC?

Pretty certain most AC systems go to re-circ on full pelt. Not much point in trying to cool hotter air from outside?

Reply to
Dave Plowman (News)

Perhaps the motoring press were confused by the power demand required by a Mini to maintain a steady 30mph on a smooth and level road, translating this into the more dramatic phrase they misappropriated for dramatic effect.

Reply to
Johnny B Good

The most effective way to avoid misted up glass when setting off from home on a cold and frosty winter's morning is to use a jug full or two of warm water over the glass to melt and rinse away frost and ice.

This has the charm of warming the glass sufficiently to allow the initially cold stream of demisting airflow a chance to get above freezing before the glass is able to cool below the dewpoint and start misting up or even freezing a fresh layer of frost on the outside. It proved very effective with my 1965 Volkswagon Beetle[1] on even the coldest and dampest of winter mornings.

The cans of de-icing fluid are a waste of money as far as solving this particular problem goes - they act as a refrigerant and will chill the glass to even lower temperatures thus exacerbating the misting up issues.

If you have the time to leave the engine idling for 5 or 10 minutes[2] before setting off, de-icing fluid can be an effective, if time consuming solution, when you don't have ready access to a jug or two of warm water. Other than that (an emergency screen de-icing solution), it's a method not to be recommended as a routine way to prepare your vehicle for its early winter morning's journey.

[1] Works just as effectively on all makes and models of cars. [2] The worst possible way to warm up an internal combustion engine - burning up fuel going nowhere and the slowest way to raise engine temperature. Far better to get underway as soon as the engine has started up and short change gears to use maximum torque to reach road legal speed.

You get higher cylinder temperature with slowest piston speed whilst the oil is nice and thick and better able to better withstand the higher pressures in the big and little end bearings. Best fuel economy with least engine wear possible during this critical warm up phase. Avoid high rpms (unless you're really really in a hurry), the piston rings, cylinder bores and the oil pump will all thank you for such consideration. :-)

Reply to
Johnny B Good

cturing places where close humidity control is vital.

That's just because the air has been dried by cooling. No attempt is made to control the humidity to any specified level.

Reply to
harry

The reason the screen clears is due to low Relative Humidity of the incoming air. The air can be warm or cold. Heating air reduces the RH. Chilling it below dew point also reduces RH. Chilling it first and then heating it has the best demisting effect of all. Not a comfortable environment though.

Reply to
harry

Nah, heated windscreen :-)

Reply to
Chris French

on 10/01/2016, harry supposed :

Precisely, which is why my indoor clothes drying system works so well. Just a desk fan to stir the air up and a dehumidifier to maintain a low humidity in the room. Much cheaper and more capacity than my drier.

Reply to
Harry Bloomfield

Makes sense - could even be designed like regenerative braking...

Reply to
Andrew Gabriel

Well it also says something about the voltage of the system rising above its "normal" level when going downhill - its own form of regenerative braking. It would be interesting to know how much it actually achieves!

Reply to
polygonum

In message , Chris French writes

  • 1 if you drive a Ford.
Reply to
Tim Lamb

The evaporator freezes up if the clutch doesn't periodically disengage.

Reply to
Mathew Newton

Yes, it should have a dedicated thermostat for that purpose. That is, in the immortal words of 1066 and All That, "A Bad Thing".

Reply to
Davey

How quaint. I just start it up and press the "demist" button which whacks the climate control to full cool and full fan to the windscreen, switches on the heated rear screen, heated door mirrors and heated windscreen.

By the time the lights and side windows have been cleared of frost and/or snow the windscreen and mirrors have cleared themselves. B-)

Big snag with the jug of warm water is 400 yds down the road the residual water on the screen freezes due to being cooled from the glass at -10 C or lower and evaporation caused by travelling at 50 mph though dry air.

Reply to
Dave Liquorice

MM. Actually it doesn't. Ive used this trick and it really works. The screen gets warm enough and stays warm enough till the car heater starts to work.

Cant say I've tested it at -15C tho. But that's when you run the engine in the drive while you get the hot water trick going and hope its hot enough to keep the thing clear once you have started to drive

Reply to
The Natural Philosopher

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