This might sound like a silly question but in terms of using air con economically as well as looking after the system, is it better to keep it on all the time when needed in hot weather? Does switching it off then back on again every so often on a journey to keep fuel consumption down do it any harm? (I have read previous threads about fuel costs and air con and know you don't all agree on this one - and I also know air con should be used at least once a month throughout the year to keep the condensor? compressor? (whatever) happy.)
I would hazard a guess and say it's best to leave it on as the lesser of two evils but you know, just wondering.
Thanks.
|
|
Have a look at Honest John's FAQs, one of which covers a/c. That said, I, like you, don't understand his answer which says that you should leave it 'selected' all the time. Not necessarily selected to a temperature where it will be producing cold air but 'selected'.. Perhaps your query will produce answers from others who know what is going on - I hope so!
|
I've got a Mondeo, 2years old and hardly ever use the air con - recent hot spell hit and guess what - it packed up. Ford dealer says it needs a new Evaporator and Accumulator. Maybe it was because I don't use it enough.
This seem silly to me, I must use a fuel sapping accessory all year, just so it works on the 10 days I really need it - surely the manufacturers can come up with something better.
|
|
|
|
Carole
Leave it on. Many cars have climate control which runs the air con all the time balanced with the heater to produce a constant cabin temperature. Although it sounds daft, run the air con in the winter with the heater on; it dries the air out and helps with demisting.
As for the economy thing; that's the price of progress ...
|
Carole
Darcy is right, and the demisting effect in winter is a huge safety benefit. I admit I don't use the aircon all the time, but it certainly gets used regularly all year round. Don't worry too much about the economy issue. Modern systems make very little difference to the fuel consumption - I'm unable to detect any noticeable differnce on my car.
Anyway in summer leaving windows or sun roofs open costs money as it upsets the aerodynamics of the car anyway.
Regards
john
|
|
|
|
Hope you're ready for this one, so here goes.
The evaporator (the piece under the dash) has a thermostat on it that only allows the a/c compressor to run until this reaches 1-2 degrees. This stops it from freezing the condensation on it, thereby blocking airflow. All incoming air passes over the evaporator, then the heater matrix, all the time, so if the a/c is on, it's on, whatever temp you set the controls to. therefore in winter, if the a/c is on, and the air entering the vehicle is not much above 1-2 degrees, then the compressor will only run very briefly until the evaporator is down to 1-2 degrees again. Consequently the drain on the engine is negligible as the compressor is doing very little work trying to keep the evaporator at 1-2 degrees. Therefore the compressor only really uses power when the outside temp is high, when the a/c is really needed anyway. So you may as well leave it on all the time. Also, many vehicles have a low temp switch that cuts the a/c if the outside temp is low, typically 4-8 degees. On vehicles with climate control, selecting the demist function will start the a/c even if the external temp is below the low ambient cut-off.
A lot of cars now have a variable displacement compressor, mainly renaults, VW's, Peugoets etc, and this compressor varies the output, and therefore the power used, depending on demand, rather like an alternator. They monitor the pressure of the refrigerant inside the evaporator, and from that can tell it's temperature (pressure/temp always related), and then the same rules as above apply. You don't hear about people trying to turn off the alternator during the day when they aren't using their light. These compressors also improve driveability of small engined cars, as you don't get the constant cycling of the compressor.
The conclusion then is as follows:- It probably makes next to no difference either way to economy, but leaving it on may bring you some small advantages in terms of demisting, dryer air etc, and longer system life. As someone in the business I would just turn it on a forget about it. Let it run like al the other things that run with the engine.
|
|
|
I too think its best to leave it on all the time and just let the system sort itself out. Though they will not operate at low temperatures. Certainly I have known more a/c problems with cars in our fleet where the driver uses the a/c only occasionally as opposed to the leave it on 24/7 brigade.
Some cars, Peugeot is one that springs to mind, have a system where the compressor is driven from an engine pulley via a electro-mechanical clutch, and according to the temperature it cuts in and out. This is an absolute swine when you are trickling in traffic as the car slows down/speeds noticeably as the compressor cuts in/out until the governor sorts out the fuel flow.
Yet on other cars it seems to be connected all the time and there is a sort of variable output from the compressor which I confess I don't fully understand how that works but would appreciate one of the a/c boys on the site explaining. To contradict a previous post I made on this some time ago I noticed in the recent hot weather that I could detect a significant difference on the instant fuel cons. readout dependant upon whether the a/c was switched on or not.
Talking of the cutting in/out this reminds me of the Norton bikes with the twin rotor Wankel engine. When you were trickling on in traffic the "engine management system" (in quotes for obvious reasons) used to cut out one rotor, but if you were still in a traffic q and it got to the engine speed where it though you needed both rotors, without warning, oh was it exciting.
|
Stuart B wrote:
>
> I too think its best to leave it on all the time and just let
> the system sort itself out. Though they will not operate at
> low temperatures. Certainly I have known more a/c problems
> with cars in our fleet where the driver uses the a/c only
> occasionally as opposed to the leave it on 24/7 brigade.
>
> Some cars, Peugeot is one that springs to mind, have a system
> where the compressor is driven from an engine pulley via a
> electro-mechanical clutch, and according to the temperature
> it cuts in and out. This is an absolute swine when you are
> trickling in traffic as the car slows down/speeds noticeably
> as the compressor cuts in/out until the governor sorts out
> the fuel flow.
>
From my experience this is very true for 1.6 petrol 405's.
Not a problem with 1.9TD 405 or 306.
The problem is a compound one - the 1.6 was a smidge underpowered
when you bolted on the air con, and the fact that you are relying on a
box of relatively slow reacting electronics rather than an almost
instantly reacting mechanical diesel pump to maintain constant engine
speed.
/John
|
I had a Toyota Corolla (1.6) when I worked in Kuwait and Saudi Arabia (I drove it from Kuwait to Saudi, this was 20 years ago!) which had A/C fitted.
Not bad for a car that cost only £1600, about the same as a Cortina if memory serves me.
When you wanted to overtake another vehicle (an exciting activity in Saudi) you needed to switch off the A/C to get a bit more power!
This thread has been very informative to me over the merits of A/C and especially "Climate Control" -----so that's how it works!
Regards,
Tony
|
|
This is now sorted also, as most a/c systems now have their own ecu, or work from the main ecu, and a large throttle opening detected by the throttle potentiometer will cut the a/c for you, as will high engine temp, low ambient, compressor revs below engine revs, high power steering line pressures, and all number of other factors. Troubleshooting a/c electrical systems used to be easy, not anymore!
|
|
|
I've driven an 1.25 Renault Twingo with air con in Italy,
The air con was always turned off when joining the autostrada,
and was sometimes called upon to act as an auxiliary brake
during some hairer moments!
As an aside the Twingo has got to rate as one of the enjoyable cars
I've ever driven - unlike many other larger/more expensive cars
it exceeded my expectations.
/John
|
John
But it's a Renault so it'll dissapoint someone sooner or later ;-)
|
Darcy Kitchin wrote:
>
> John
> But it's a Renault so it'll dissapoint someone sooner or
> later ;-)
But a Twingo is so cheap as to be disposable!
|
|
|
|
|
|
Dave, thanks for answering my simultaneous post in advance, if that make sense.
Stuart
|
|
|
|
Thanks everyone. I understand it all now. I think.
|
|
|
Re Stuart B's: "the car slows down/speeds noticeably as the compressor cuts in/out until the governor sorts out the fuel flow."
John Kenyon wrote:
"Not a problem with 1.9TD 405 or 306."
However, I find that there is a noticeable "jerk" as the compressor cuts in and out on my Pug 405 1.9 turbo diesel. It feels as if the engine has "missed" when it cuts in.
When idling the revs drop about 100 rpm as it cuts in, and back up as it cuts out.
Sorry if this does not accord with your experience. Do I have a fault?.
Brian
|
Brian wrote:
>
> Re Stuart B's: "the car slows down/speeds noticeably as the
> compressor cuts in/out until the governor sorts out the fuel
> flow."
>
> John Kenyon wrote:
> "Not a problem with 1.9TD 405 or 306."
>
> However, I find that there is a noticeable "jerk" as the
> compressor cuts in and out on my Pug 405 1.9 turbo diesel. It
> feels as if the engine has "missed" when it cuts in.
> When idling the revs drop about 100 rpm as it cuts in, and
> back up as it cuts out.
>
> Sorry if this does not accord with your experience. Do I have
> a fault?.
When idling I get the same behaviour.
The original post was talking about the kind of situation where you
are sat in a queue in 1st gear, controlling speed using just the
gas pedal. When you're idling, all bets are off as you are relying on
the anti-stall settings to manage engine speed, just to stop the thing
from stalling.
/John
|
|
|
|
I don't think you have a fault. Earlier 405's had an older style of compressor that cycles on and off, and they all cause this problem, to a greater or lesser extent. Now you know why they are moving to the variable compressors. Don't forget that at tickover an engine is only producing something like 10 hp, so turning the compressor on can be quite a load. On the older diesels that usually have vacuum device that brings the idle up, where the electrical power to the compressor also goes to energize a vacuum valve, pulling on the throttle arm on the diesel pump, but slop in the linkage on the diesel pump usually means that it all gets out of sync. All later diesels are electrically controlled and this manages things a whole lot ot better.
|
|
|
|
