Air-Conditioning Issue Solution

[Andetover]

I have a slightly weird situation with my air-con. It was getting really chilly on the passenger (right hand drive, UK spec) but only tepid on the driver's side.

Reasons posted for this common complaint are many and varied, some say low refrigerant means it only cools one side of the car, others say that the stepper motors that control the flaps get out of alignment.

Now I've been able to do a partial fix.
My model is a 2005 CLK350 SPORT.

To realign the flaps you press the FRONT window demist and the recirculation buttons together for about 4 seconds. The amber and red lights on the buttons then flash alternately for about another 5 seconds before going out, and the heater flaps/motors reset. Apparently this is something that should be done at every service.
The result is that now the air on the driver's side does get chilly, albeit it takes a little longer to chill right down.

This was visibly discernable when I put the heater (with aircon on) onto a cold windscreen. Initially it misted up (warm moist air hitting cold glass) then after a few seconds the passenger half cleared. It took about 45 seconds for the driver's side to catch up, and dry the air.

I'm currently waiting for a "formula one autocentre" to check and re-gas the system.
The system very recently had all the gaskets replaced (with genuine Mercedes supplied "O"-rings), a pipe to the compressor replaced, and a new condensor with filter/drier.
It was re-gassed, but they didn't have a machine to bring about the sufficient negative air pressure needed before adding the refrigerant (-2 bar), and so although it undoubtedly worked, it wasn't quite right.

If this re-gas and pressure test works I'll let you know, with the added information that either it's true, low levels do result in it getting colder on one side than the other, or no, that's just another myth causing misdirection.

 

[Andetover]

Well, I have to say it's "ice cold" all over now, right where you want it.
Lovely
However, within literally a couple of miles of thinking "Finally, everything is working as it should, no more unscheduled expenses now except fuel and shampoo" when a BMW M3 had to overtake fast and cut in (trying too hard to be faster than an AMG) and CRACK!!

Non repairable stone chip.
Booked in for a new screen via my insurance, on Dec 29th. They promise like-for-like, it had better be, I'm getting hacked off with having to correct mistakes made by garages.
The impact dent itself is about the size of a 5p, but the spread of the cracks is the width of a 20p piece.

I bought the car in August, it then spent 2½ months in 3 workshops (the second one had to fix dangerous issues caused by the first one), I've driven the car maybe 12 times in total, and having spent £4k on replacing everything from the water pump, rad, air-con components, coolant pipes, brake calipers, brake hoses, tyres, gearbox oil/filters/pan, differential lubricant, new underseal, and air pump for the pneumatic seat pillows. And interior seat trim, oh and parking sensors and polishing the headlamp covers.

Now it's going to be treated to a new windscreen.

It's Trigger's Broom reincarnated.
But faster.

 

[WOODYTHEWISE]

Ouch!

 

[Andetover]

Ouch!

Trouble is, it's such a bloody good car, and handsome like it's owner...

 

[WOODYTHEWISE]

Yes indeed....

 

[alabbasi]

Needs freon. Put gauges on it and read the pressures.

 

[Andetover]

Needs freon. Put gauges on it and read the pressures.

That had already been done. The 3rd mechanic I took it to (electrical specialist) who knew the second one, showed me the levels after I commented that despite having a load of new parts (including ALL the O rings replaced and a new condensor/drier unit) it wasn't getting that cold (although this was when we were getting outside temperatures of -3 so it wasn't that easy to diagnose).

Turned out that although refrigerant had been put in, because he had used a DIY bottle, he hadn't been able to remove enough of the atmospheric pressure thereby making it harder for the refrigerant to evaporate and remove the heat. And the vent flaps did appear to be out of sync too.

 

[alabbasi]

I'm not sure what that means. But if you're saying that he could not add a change because the compressor did not want to take it due to high pressures in the system, an easy way to fix that is to hose the condenser with water while you're adding Freon so that you can drop the pressure.

Although seeing high numbers on the high side can be the cause of a blocked expansion valve or air/moisture in the system from improper vacuum.

 

[Andetover]

In order for an air conditioning system to work efficiently you need to reduce the evaporation temperature (boiling point) of the refrigerant. To do this, prior to charging the system with new liquid, you need to cause a vacuum in the system, typically with a negative pressure of 2 bar. The advantage of doing that is that when the system pauses between extracting the air, and charging the system, is that the pressure can be monitored, and any increase would indicate there is a leak.

Just pumping more Freon in wouldn't work, it needs to be in a system that has less than atmospheric pressure.
The problem with the DIY top up kits is that they don't have a pump to extract the air to create sufficient loss of pressure, so in a pressurised system the refrigerant boils at a higher temperature which means that it's less efficient. My system had already been checked by a "mercedes specialist" who forgot to check the system for leaks despite having the car for over a month (!!) and the second garage, although they methodically checked every component was working and replaced many parts, lacked the necessary machine to create the vacuum.
My system DID work, but the pressure in the high side was too high, and putting more gas in wouldn't have helped. It was cooling the air, but not making it really freezing enough to keep the cabin from steaming up.
Anyway, it's done now, third time lucky.
Except for the stone chip in the window less than 10 minutes later.

 

[Phil1968]

The primary purpose of pulling a vacuum is to lower the boiling point of any moisture in the system, so it will be drawn out as a vapour, also to make sure there is no air in the system so that there is nothing but refrigerant taking up that space. Secondary, when connected up to the automatic machines that car workshops use, it's used to detect if the system is leak tight, although this isn't the best way as a vacuum is only the equivalent of one atmosphere (minus 1 bar). The proper way to leak check is with a nitrogen pressure test to at least the system working pressure (on the high pressure side of the system that is at least 15 bar). I would also be dubious about using the DIY top up cans as the refrigerant needs to be weighed in to a specific amount from empty (with a vacuum pulled beforehand) to work optimally. With one of those cans you're just guessing.

 

[Andetover]

The primary purpose of pulling a vacuum is to lower the boiling point of any moisture in the system, so it will be drawn out as a vapour, also to make sure there is no air in the system so that there is nothing but refrigerant taking up that space. Secondary, when connected up to the automatic machines that car workshops use, it's used to detect if the system is leak tight, although this isn't the best way as a vacuum is only the equivalent of one atmosphere (minus 1 bar). The proper way to leak check is with a nitrogen pressure test to at least the system working pressure (on the high pressure side of the system that is at least 15 bar). I would also be dubious about using the DIY top up cans as the refrigerant needs to be weighed in to a specific amount from empty (with a vacuum pulled beforehand) to work optimally. With one of those cans you're just guessing.

Thank you. This is why I find it mildly frustrating that people say "Oh it's low on gas, just put some more in", it's not that simple, and why it's important (if you're going to take it apart after it's not been working for a while) to change the seals, and the dryer, and clear out any condensation, in fact although the original condenser seemed to be OK (apart from some broken brackets and a leak at one of the joints to a pipe entering it) I said for the sake of about £100, just get a decent new one (via AutoDoc) and then you're not worrying about blocked galleries or water contamination. And we changed the filter/drier at the same time, they nearly always get neglected.

The reason why I was getting a little anal about the air-con (previous owner never used the car in Winter, and drove with the top down so claimed he never knew it wasn't working) is that some of the rear window demist bars aren't working. It's actually not too bad, but if we can keep the cabin air dry (through using the air-con) it stops the rear misting up.

Changing the rear window is something I looked at, and the horror stories I had back (massive cost plus possible damage to the folding roof if the alignment is nudged out of kilter) made me think that it's probably best to let sleeping dogs lie.

I just want to enjoy the thing, I'm not worried about some stone chips in the paint, or even a light scuff on the rear offside corner of the bumper (really just a rub in the paint) because if it was too perfect, I'd be forever putting off driving it in case it got damaged. But the bloody windscreen completely blind sided me, it's so bad that it risks cracking the whole glass eventually, although it's currently just under the front drivers wiper blade, so not in my line of sight from the drivers seat, but from outside its like a sparkly piece of tin foil stuck to the window.

Now here's a thing. MB quoted me £242+ VAT for a genuine replacement. I've seen aftermarket ones priced at £400. Go figure.

 

[Andetover]

No disrespect intended, but we are talking about 15+ year old air conditioning systems as fitted to automobiles, which is completely different to a domestic air-con in so much as the ones you are describing are run on electricity, and the ones on a car a run mechanically from the ribbed auxiliary belt powering a compressor. I'm not sure about your reference to mirrors on this thread either.

Mirrors are generally streamlined into the doors, and provide a reliable image regardless of whether your ignition is on, or there are any wiring/software glitches. Unless you want to record what is going on, cameras are an answer for a problem that really doesn't exist (apart from blindspot reversing cameras).