General MOT failure & other Things/Stuff

[Pugglt Auld Jock]

although, I believe, it doesn't operate in extremely cold conditions to prevent the liquid freezing and solidifying as it comes out of the nozzle in the evaporator? Seem to remember reading that somewhere? However just keep it on and let it do it's thing.

 

[vexorg]

The air con pump is turned on and off according to the gas temp, not the temp you demand inside. On a cold day, the gas will warm up very slowly, so as John says above, it only cycles a little. On a warmer day, it will cycle more frequently.

Not quite true, it will be indirectly controlled by the demand inside. And on a cold day, it still needs to run to compress the gas into liquid, after that it may not run as often, but still needs pumped round the condenser to lose the heat it has.

 

[jrkitching]

although, I believe, it doesn't operate in extremely cold conditions to prevent the liquid freezing and solidifying as it comes out of the nozzle in the evaporator? Seem to remember reading that somewhere?

The reason A/C is usually inhibited at low air temperatures is that the moisture in the air flowing over through the evaporator matrix can freeze, blocking the airflow.

You can see this on a home dehumidifier; in colder weather, when ice collects on the evaporator instead of water. Most dehumidifiers go through a periodic defrosting cycle to warm up the evaporator and thaw out any ice.

 

[vexorg]

although, I believe, it doesn't operate in extremely cold conditions to prevent the liquid freezing and solidifying as it comes out of the nozzle in the evaporator? Seem to remember reading that somewhere? However just keep it on and let it do it's thing.

Do you need it on at -10°C outside?
It boils at -26°C and freezes at -103°C (at atmosphere), not sure it will ever solidify in the system under normal conditions.

 

[jrkitching]

Do you need it on at -10°C outside?

Regardless of whether it's turned on or not, I doubt the compressor would run once the temperature drops below freezing. Most A/C systems will have an outside air temperature below which running is inhibited. I'm not sure about Fiat's system, but on my last Ford, the control system prevented the compressor from being engaged once the OAT fell below +4C.

In freezing weather, just using the heater (providing recirculation is turned off) will do a pretty good job of dehumidifying the inside, because there isn't much moisture in the outside air; you'll be getting warm, dry air out of the heater anyway. It's on those warmer (>10C) days with high humidity when running the A/C has the most beneficial effect at drying the inside of the car.

It boils at -26°C and freezes at -103°C (at atmosphere), not sure it will ever solidify in the system under normal conditions.

The refrigerant won't freeze, but if it gets too cold, ice may form elsewhere in the system, from the moisture in the surrounding air.

 

[GettinBetter]

Cheers peeps, lots of lovely info to digest. Thank you.

 

[Baglady1990]

I'd have my doubts on the airflow, or how long it would least.
The older juke has the same issue, no front grill to protect the aircon. I got some hlafords black alloy mesh and bolted it on. Looked quite nice when done.

Air flow is fine had no issues and the mesh is coming up to 3 years old holding on fine!

 

[steveras57]

Like your mum told you always use protection!

 

[John202020]

Arrr, having driven cars with AC from 1984 ( all Honda Accords had AC as standard on the EX 4dr models from 1979 ) just leave it ON! the system sorts itself out, the condenser stays hot and dry so lasts longer 20+ years we found, I really can't under stand why people use it the way they do?

 

[vexorg]

I really can't under stand why people use it the way they do?

Traditionally they were very heavy on fuel.

 

[Pugglt Auld Jock]

Traditionally they were very heavy on fuel.

that's what I always was told. However I'm also aware that the seals can dry out if not used which often results in a new compressor being needed. I make a point of running mine every Tuesday when we have a 20+ mile round trip to look after the grandchildren. Seemed to be a good strategy until it stopped working late on in her 4th year. Got it recharged but it stopped working after a month so I've just lived without it since then - don't really miss it. I was honest and mentioned it to the salesman when he gave me a trade in price on her but he didn't reduce the offer, which surprised me.

 

[John202020]

To be fair my Honda accords like my 2.2l SE estate would only do 23mpg round town in winter so the ac made little difference in fuel economy and was easily worth the comfort in summer, I accepted the trade off, though I did have to constantly say to the public that said the car was leaking in summer in the 80's it's OK it's supposed to do that as a lake formed under the car

 

[There all puntos]

Non of my previous transport every had AC, until in July 2018 I purchased a Citroen Cactus, it has manual type Aircon.

I new a bloke that used to work on Air conditioning systems. He told me always on is ok for a building. But not for your average compact type car.

He advised me (and my boss) in 2002 that air conditioning needs to be run for a minimum of five minutes a day, or in winter five minutes once the car has heated up once a week.

My bosses 2002 C5 had manual AC (like the system I have in the Cactus now) his and my system both have a 'Instant' windscreen defrost button on the dash, under the media display. And said 'once your car has started press it for as long as you want'.

Or in all seasons for five minutes minimum, as the 'instant' button also puts both the Aircon and full blast heat to stop it gumming up the seals and to run the motor.

And defrost your front windows in winter.

It also has a AC button on the media display (along with) all the heating, radio, Usb, 3.5mm in control, the onboard handbook, photo access from the Usb and to play mp3 files but not mp4 videos. et al.

 

[yann]

Interesting stuff, a.c. is part of my job-the state of the fiat condensers ( the 'a.c. rads') is normal as iin most modern cars with open type grilles.
I see loads where the fins have 'jumped ship' as discussed peviously.Also i see massive distortion in some condensers...ssangyong, hyundai, kia, etc...
(still working though) the missing fins only slightly reduce efficiency at first.....takes a lot to really make you go phew'!!
they are important though....if you hooked up refrig gauges to a system, (with missing or blocked fins) read the gauges & monitored the cars interior temps, then...blew an air line (carefully) through the condenser.........happy days! just my ramblings, might help someone.