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Hi,

Been doing some diy on my wifes eos , 2007 , uk , 60 ish miles , 2.0 tfsi , and noticed this 'frosting' on the aircon pipe . see pics . Looks like a white plastic pipe due to frosting. Heating and aircon seem to work fine during approx 20 - 30 min trip and vcds scan shows no errors . it was approx 10 degrees outside .

DIY work was none air con related , and I've not noticed this before .

Any ideas , is this normal , or a fault . a quick google doesn't help. i will give the car a longer test drive tomorrow to see if cold air stops coming out of the vents i.e. system frozen up sold.
p.s the has has climate control

Regards
 

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Hi there

Most likely just down to atmospheric conditions. As you said, check if your condenser freezes. Doubt it, though.
 

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Hi, I've not noticed it on MY07 but I'll look. :confused:

Hard to understand why you would see it in the engine compartment now which should be the warmest part of the car. My aircon plumbing is all ali. If the outside air temp is 10C and you want your cabin temp around 18-20C I can't see why you would need to mix cold air from the aircon? I don't have full climate control, but why are you getting cold air into the cabin from air con when it's that cold outside. The only way I can force that with my manual control is to turn it to fully cold?

When I start up from cold I initially get cold air, but at about external ambient temperature as I would expect. After a mile or as the temp gauge starts moving up I'm getting hot air. :) Most car aircons will cool air to about 15 deg. below external ambient, which could put your condenser at -5C and below frost level. But why is it running in Winter? :confused:

You said you are testing to see if (very) cold air stops coming out of the vents, but why should that be coming from the aircon? Put a thermometer in the air stream and set the climate control for about 18-20C and fresh air. From a cold startup I wouldn't expect air temperature from the vents to be below outside temperature. If it is, the air con is cooling for some reason? Car aircon systems can work in odd ways e.g. cycle between air con cooling and the hot heating matrix to produce an average required temperature. But I wouldn't expect these to be big swings. If your climate control has an ECON mode, try turning it on and that should turn off the compressor and increase mpg, although Climatronic isn't supposed to work below 4-5 deg.C anyway. VCDS may not show an error if there's a temperature sensor off calibration, the system will work assuming that is the temperature you called for.

There's probably nothing to worry about unless you are getting sub outside air temperatures from the air vents when you expect 18-20 deg. C. If you were getting really low temperatures, condensation on your screen would freeze over when you selcted the screen defrost vents.
 

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The icing of the compressor inlet pipe is a normal everyday occurrence in our climate - the severity depends on the relative humidity; high humidity = high icing, low humidity = low icing.

A very cold return line indicates not much heat is being picked up from the interior air so very cold refrigerant is returning to the compressor.
 

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Is the compressor running all the time and cold air is mixed with flaps , or is it clutched and driven on demand?
 

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Is the compressor running all the time and cold air is mixed with flaps , or is it clutched and driven on demand?
Clutch driven and cycles based on air temperature leaving the evaporator under the dash.

Pre-electronic engines also have a vacuum-operated "idle-up" linkage which increases engine speed to preventing the engine stalling from the extra load coming from the compressor.

Have not had a chance to look at schematic or other information regarding electronic controls on our MY18 Mazda CX5 diesel however I have not noticed an idle speed change whilst the vehicle is stationary so the compressor output may be variable by a bypass or throttling valve rather than "stop/start" regulation.
 

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Discussion Starter #7
Hi

Thanks for the prompt replies .. did a longer run today and checked and the larger aircon pipe was frosted over again as per photo. Hot and cold works as expected

From whats mentioned above it would seems it's normal .

Also noticed that both fans had been running when i looked under the bonnet which also seems to be normal operation

Will have a more detailed look with vcds and post the output . The car had a recharge approx 18mths ago with no problems reported .

Again thanks for the help ...

Sent from my SM-G950F using Tapatalk
 

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Idle speed 'compensation' is done in the ECU. It takes inputs from various places including the alternator and aircon compressor. You can often hear idle speed increase slightly then drop back when the compressor clutch kicks in.
 

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Discussion Starter #9
Hi

I see , makes sense as I can see rpm's drop when the a/c is switched off at idle. With a small increase when it's switched back on .

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Hi there

You should regas every 2 years or so. The system can lose upto 25% gas a year. Ps. Gas prices have rocketed recently, so shop around.
 
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