"lots of other cars have the same issue including Lexus"
Yep. My Lex took an age to demist tonight.
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My Lex took an age to demist tonight.
What you need is an electrically heated front screen as per my humble Focus.
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L'escargot by name, but not by nature.
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It's likely that the boiling temperature of the refrigerant in the evaporator (the part that is in the air flow) is around 4°C. Any lower and any water that is condensed out of the air will freeze onto the evaporator and stop it working. Hence if the air temperature is below 4°C nothing will happen. It may be that on cars where it appears more effective the matrices may be arranged the other way around - eg heat first then cool - you might then be able to knock some water out of the air before it hits the windscreen.
RichardW
Is it illogical? It must be Citroen....
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I read more of the manual last night, so I think I can answer my own question now! It's the old shape Mondeo with basic air con and later in the book it says if you direct air to the front screen the a/c is always on! So I will try this rather than the rapid heating of the interior setting, which doesn't send air to the screen.
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The boiling point of the refrigerant is -30 degC.
As the systems are designed to keep the evaporator just above zero to prevent freezing, the a/c will only operate the compressor for a short while anyway, as within a second or two, the evap will be down to zero and the compressor will stop.
Some will ignore the zero point when in defrost mode, but not for long, to prevent freezing.
That's why running the a/c in the winter makes no difference to fuel consumption, as it only actually runs for a very small amount of time necessary to keep the evap around 1 deg.
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Dave,
Does that mean the advice often given about running the air conditioning regularly even during winter to circulate oil around the system to keep the seals lubricated is not valid if the compressor won't actually be running at these low ambient temperatures or am missing the point?
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And how does all of the discussion above relate to VW's climatronic?
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Now aint that amazing. My car took an age to demist on Monday night as well. I see from the thread about the windscreen change on a golf, that that took an age to demist that day as well. It was ok in the monring, but took ages and ages in the evening.
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twinexhaust, it will run sometimes, just not for long, so the advice is still valid.
However, in my years as an a/c specialist, I can't honestly recall fixing any systems that I could honestly say had failed due to lack of use. Virtually all of them have failed due to external corrosion, pipes rubbing/corroding through (though some of it could have come from inside out), fractures, compressors falling apart, switches quitting, wires broken etc.
On cars with variable displacement compressors, the compressor will run all the time the a/c is on, but with minimal gas displacement. There has been some talk in the industry that this can cause oil starvation as the volume of gas, and therefore it's ability to move oil, is very small. Some newer VAG and mercs have a compressor that runs 100% of the time, whether the a/c is on or off, and the displacement is controlled electronically, so on these cars you don't have a choice, if the engines running, so's the a/c compressor, just like the alternator and PAS pump.
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Thanks for that Dave - very interesting. Any idea what type of compressor or control system the new shape Mondeo climate control has? When left in auto the A/C light is on all the time but in light of your post am wondering if the compressor cuts in or out or runs continuously or is controlled otherwise. Thinking of fuel consumption really. I assume the compressor is belt driven so if cutting in and out how does it get de-coupled? Some sort of clutch system?
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If it's the latest shape Mondeo, then it has a variable displacement compressor, a Denso design made under licence by Visteon. So it runs all the time the a/c is called for, but has a clutch on the front to cut it out if needed. Fords used to have a low temp cutout circuit, though in reality it isn't needed as the pressure of the refrigerant drops with temperature, thereby doing the same job.
At minimal displacement, which it will be when there is little demand, it only consumes about 250 watts of power, about the same as having your lights on, which is basically negligeable. Ha, the way I look at it, there's more important things to worry about than whether the compressor's running or not.
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Yes, latest shape Mondeo so thanks for the information. Think I'll just leave it on and forget about it now.
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Dave - I've followed this thread with interest.The A/C certainly seems effective in demisting my Honda whether in warm or cold temps although it does seem to take longer in the cold.I never really thought about it that seriously. I am interested in what type of compressor is installed in my (latest shape) 'X ' reg Civic and Mrs H's Yaris.
Are you saying that we might as well justleave the A/C on all the time?
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Helicopter, I think both your cars have a traditional cycling compressor. In other words, they come on to cool the evaporator, then go off again. The greater the load, the longer they stay on for. I've not seen a Yaris yet, but I believe it to be the same type. A bit like the your central heating boiler, the higher your thermostat, the more the boiler comes on for.
You can just leave it on, as it won't run much due to the small heat load. The only problem you get with this type of compressor is the constant on-off, which with a small engine can spoil the driveability a bit. That's why most manufacturers are moving over to the variable displacement type that runs all the time.
Strangely enough, even though Denso make a variable compressor (and Denso is owned by Toyota), Toyota still use the cycling compressor type on all models. The japanese are pretty canny, they like to let others try things out first!
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Dave - Many thanks for the info. We'll be leaving the A/C on all the time and see how it goes. It may be more of a problem with the Yaris as its only a 1 litre.
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Very interesting, i guess the Focus is not alone. Dave, can you tell me what my 99 Focus 1.6 LX might have (cycling or constant compressor). I think this thread has answered my questions.
Thanks
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Toyota haven't owned DENSO since 1949...!
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It's not wise to leave A/C on all the time.... It also increases fuel consumption.
My VW Bora's A/C only works when the engine is running, the ambient temperature is above about + 5 degrees C and the blower speed between one and four.
There are times too when the air recirculation mode cannot be switched on depending on the position of the rotary regulator - this is to prevent the windscreen misting up.
That may be part of your problem.
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Using aircon makes moisture condense into the aircon/heater system, and it doesn't all drain out. The residual moisture can then be blown into the car when you switch the aircon off. For this reason I find it's better not to use aircon in winter in an attempt to improve demisting. I've tried using aircon, and it's OK until you switch it off ~ after that misting up is even more of a problem for several days until the aircon/heater system has dried out. Several colleagues at work have had the same problem, and have come to the same conclusion. By all means turn the aircon on periodically in winter to prevent the compressor seals becoming damaged, but don't use it routinely.
Start the engine the minute you get in the car (i.e. don't blow on your hands to warm them up because you'll be blowing your humid breath towards the screen), set the heater immediately to maximum heat and maximum airflow to the screen (to minimise the initial misting) and leave it like that until the screen is well and truly demisted. Then you can consider your own comfort.
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L'escargot by name, but not by nature.
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"It's not wise to leave A/C on all the time." I wonder why, apart from the fuel-consumption issue.
The A/C in my MB is on by default; in my previous MB (same model, two years older) it was off by default. Interesting change. And, as my A/C servicing chap says, basically, "use it or lose it", I use it.
And, for what it's worth, here's HJ's advice:
tinyurl.com/wz2r
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wow what an interesting thread. I had no idea there was so much to air conditioning!
My new Corolla (S reg) arrives tomorrow and will be the first car I've ever had with air con. Until I get my paws on it and have a good look through the manual I'll have no idea how to get it to demist the windscreen! It's all new to me.
Great info on this thread, thanks :)
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I'm suprised the Mondeo in question doesnt have the heated screen, tbh.
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