CANT DRIVE AT ALL NOW WiTHOUT ac ON ALL THE TIME!

[Ger D]

Guys, I'd like your opinion and advice on this one. Got a 98e300td, w210.025 .

My Problem: at fan setting 2 0r 3 air flow always seems very weak. A few days ago, 5 very wet people got into the car and with the expected increased humidity every window fogged up.

Only managed to maintain a clear windscreen ever since with AC on. Thought for the 1st day or so that leather interior was retaining moisture at an increased rate over velour but the problem still persists, so much so that I CANT DRIVE AT ALL NOW WiTHOUT ac ON ALL THE TIME!

One other thing to note, possibly related, When trying to clear windscreen quickly at full speed (5) and direction control wheel pointing at the Windscreen symbol fan runs for a couple of mins, with what I'd consider dissapointing force. The fan seems to cut out on perhaps a "high temp" cutout.

Time and a power cycle(remove & then replacement of key) gets the fan back to its poor performance. Read some other similar threads but nothing else sems to replicte this particular problem,
I'd appreciate your thoughts
Thanks in advance

 

[guydewdney]

first thing id do is change the filter - or at the very least give it a damn good hoover its prob overheating at full tilt as theres not enough air flow over the motor.

as a TEST only - take the pollen filter out (make sure not in a dusty / leafy area...) and try runnign the fan...

the filter is probably near the firewall under a cover, i dont knwo its location on tyour car off the top of my head.

 

[jberks]

Hi,
Guy's advice sounds good to me and certainly worth trying first, but,
Does the fan squeal, whine or sound noisy. There is apparently a power regulator on the fan that is known to fail. It sounds like a fan bearing or leaf but is actually the electronics. Mine appears to be getting worse and I suspect that the air flow doesn't increase as it should as I turn up the power. I guess this could cause the symptoms you describe. I had to run the aircon a few times this morning to clear the windows, just due to the moisture in the air generally so its normal at this time of year. In fact up to recently, I never turned it off, plus if left off for long it can apparently cause problems with seals drying out etc. May be worth keeping the air con on more anyway. I have raised a post here on replacing the fan, but no one has responded yet.

 

[190surgen]

As guydewdney says change the pollon filter most likely to be the cause have seen this many times on different makes of cars including mercs they only cost around £15-£20 hope this helps.

 

[Ger D]

Thanks to you all for the replies opinions & advice.
I dont have a Garage so it'll probably be Saturday morning before I get a chance to investigate and I'll report back.
In response to the Noise question, there's nothing like the type of noise you describe so maybe thats a bit of luck and I'm only dealing with some overdue filter replacements.

As a matter of interest, with the AC on (ie not in economy mode)is it as heavy on fuel consumption when its pumping out warm air?
I wouldnt have thought so but if someone knows for sure please tell.

Thanks again,
Ger

 

[mlc]

Ger,

I agree with what the other guys have said, when we bought our SLK the pollen filter was blocked and had a pile of leaves on top stopping the fan.

On the subject of fuel consumption and running the air con, yes it does use more fuel.

I have had air con on all my cars for the last 17 years. With each new car (all Fords) the owners manual has become more forceful in explaining that using the a/c is "ungreen" and bad for the environment. The latest one has full climate control but only brings the a/c in under extreme conditions. I was amused when I realised in the SLK that the warning light told me when a/c was turned off and therefore in economy mode. In terms of the actual cost, I used to use about 10% more fuel with a/c in the early 90's, but I suspect these days its nearer 5%.

Mark.

 

[Ger D]

Hi Mark and thanks for the response.

I'll be pleased if I find its as simple a solution as that and as I said, I'll keep you posted on the outcome.

My question regarding the AC was whether its as heavy on fuel consumption to have the AC unit blowing warm air now that the winter is in as it is to have it blowing cold air in warmer weather.
I recall an air conditioning engineer some years ago telling me that cold air was much more expensive to produce than warm air and I wondered is the same true for the MB AC set up. Does the AC unit derive any of its heat from the engine for example when its calling for heat?

Not important really, just one of those little things that I wondered about.

Regards
Ger

 

[SLinKyjoe]

Boring tho this is.....turning the heat control up with the a/c on wont make any differnec to the power consumption. the a/c compressor and such like is working while you are having heat through it. when you turn it down to cool it is still heating...just heating coolness.....that dont make sense but you will see what i mean if you get a mechy's expaination of how these systems work. just dont fall alseep while they drone on a great lenght...your fuel consumption will stay the same warm or cool with a/c on. unless you drive more fast in summer that is.


As a matter of thought when you sort your car out give the windows a really good clean inside. this helps no end. in winter you will need to clean them good and proper every 2 weeks or so. you will notice an effect! just dont clean them till you have tried your a/c out after you have fixed it. I could have waited to post this really couldn't i?

Hope you fix it soon.

 

[jberks]

good point Joe, when I start to need the rear demist, I know its time to clean inside of the rear window. I try not to do it too often as I don't want to risk busting the elements and its a bugger of a job.
As far as fuel economy goes, I get another roughly 1-2mpg (33->35) on a motorway run without the aircon - so about 5%. I suspect its far worse with lower powered cars as the HP required to run an aircon system is the same whether you have 70 or 300hp to throw at it. Try switching on the aircon on a Fiesta and watch the revs drop, then compare it to the merc which doesn't seem to notice.

 

[mlc]

I agree with the most of the items in the last two comments, I dont think that the air temperature into the cabin effects how much energy the A/C is using, so the cost in fuel is fairly constant all year around.

I do however disagree with the idea that larger engines have horse power to spare so dont cost as much to run the a/c. The fiesta example is spot on, one of our kids has A/C on a Ford KA, the engine idles badly and has no get up and go when she turns it on. I think that the loss of revs/poor running is more to do with the quality of the engine managment system when compared with a Merc. Secondly the output of the a/c on the little car will be much lower, if you fitted an MB a/c unit on a 1300cc engine I suspect it wouldn't even run! Therefore the power drain from the a/c has to be balanced to what the engine can afford, so big engines have big a/c units = similar fuel overhead.

Mark.

 

[jberks]

Mark,
I agree that smaller engined cars have smaller Aricon systems (my mums smart's system is hardly noticable when its on, except for the performace drop)., but even a small system will need a minimum amount of power to run at a level that makes it worthwhile. After that a small increased load should produce a drastically larger return. So Fiesta (60hp?), aircon loading say 3 hp and Mercs (200hp) say aircon=5hp (made up numbers). 3/60=5% of available power and assuming engine is flat out. whereas 6/200=2.5% so in theory, the effect on the Merc should be comparatively half. Factor in that the Merc will produce a lot more torque lower down and the effect is increased further. As many smaller engines produce their power higher up the rev range (16v etc), they will have to work a lot harder to make up the difference. This is also why the smaller stuff struggles at idle, it barely produces enough power to keep running at 700rpm, but then the fuel efficiency is great. Compare it to your merc, guzzling the stuff in traffic jams - but pulls sweetly from 900rpm.

All this should make for a less comparative engine load and hence a proportionately lower increase in fuel usage. The litre quantity of fuel required to run the Merc system will still be more, but as the car uses more fuel anyway, the percentage change is actually less noticible. Just depends on how you look at it.

I suspect a lot of the stories regarding how bad aircon is for fuel economy are based on the old days when engines were lower powered and aircon systems less efficient . I remember an old 300d taxi driver having to switch off the air con to get up a particularly steep hill many years ago.
My theory anyway.

 

[Ger D]

Update and Result

Thanks again to all of you who responded.

I cleaned the main/pollen? filter in the Fan Unit today.
Its comprises a tightly pleated synthethic filter element in a plastic frame, measuring about 12 X 10 inches. Passenger side footwell, under the dash,
Slide back two white sleeves to remove the retaining plate and It drops out of the fan unit just after the fan.
Not sure if this is the pollen filter, but blowing it out with compressed air has made a considerable difference. I'll replace it during the week.

Once again, my thanks.

Ger