AC Experts please!

DRZ

DRZ

DRZ

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Hi,

The AC in the S-Class was cold when I got it, just not as cold as it could have been so I suspected low gas but it was cooling the car adequately so I thought I'd get it gassed at the end of the summer when everyone has offers on the regassing.

Two weeks later and it throws a fault code on the AC system, low gas. Not a problem really, just meant £50 to regas instead of £25 or whatever. Get it done at Kwik-Fit figuring it is just a machine, how can they get it wrong? They measured the before temp at about 14c, afterwards it was 6c and falling so very, very cold. I was happy and paid up.

That was Saturday. Sunday, Monday and Tuesday were quite cold and rainy up here so I didn't have cause to notice the AC (it is very, very good in the S-Class at just keeping out of the way, never blows air straight at you etc etc)but yesterday was a bit warmer and I was melting in the car. The AC was blowing air at ambient!

No fault codes have come up to indicate low gas levels or compressor issues, anything like that. So, my question is this:

Can too much gas cause these symptoms? One or two people around the internet seem to suggest this is possible but I don't fully trust that.

I'm going to go back there and tell them to make it blow cold again and not put as much gas in but I like to know everything there is to know about what I am complaining about beforehand!
 
Too much gas would also throw up compressor errors, so I don't suspect that is the problem. They are also, as you say, machine filled and will only fill the right amount of lubricant/gas mix for the system they are charging (known charge weights on their systems should ensure this).

I'd imagine that there is either a slow leak, causing a loss in pressure, or you have having condenser problems.
 
Im more of a building AC guy but as the S class is nicer than most buildings I would guess it will have low/high pressure switches that will stop the compressor from running if its over/under charged.
 
paradigm said:
Too much gas would also throw up compressor errors, so I don't suspect that is the problem. They are also, as you say, machine filled and will only fill the right amount of lubricant/gas mix for the system they are charging (known charge weights on their systems should ensure this).

I'd imagine that there is either a slow leak, causing a loss in pressure, or you have having condenser problems.
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If it was leaking enough to be low pressure then it would have disabled the compressor and thrown an error like it did the first time?

I have read at least two forum posts saying that they have put in the wrong model or year or whatever for the car. Mine only has the front AC so needs 10% less gas than if it had "full" AC, which is why I was thinking they might have overfilled it.

I'd be more concerned about a condenser issue if it wasn't blowing fairly cold before the regas, but I suppose the increased pressure could have damaged something?
 
You could always fight cowboys with cowboys, take it to Halfords and ask for their free AC health check, they will tell you if its over/under charged, at least that way you will know for definite before storming into Kwikfit.
 
Whilst I imagine the AC is somewhat different on a BMW (perhaps) I had a similar issue after getting my e38 re-gasses. The AC stopped working almost immediately and a trip to Knights BMW diagnosed too much gas in the system.

10 minutes in the workshop (and no charge) and the AC was bloody freezing again! :)

I recall the chap @ BMW saying Halfords, Krap fit et al don't measure the quantity of AC gas correctly or something like that, I guess the shove the same volume in regardless to what car its going into?
 
R420LA6X2/4MNA said:
Whilst I imagine the AC is somewhat different on a BMW (perhaps) I had a similar issue after getting my e38 re-gasses. The AC stopped working almost immediately and a trip to Knights BMW diagnosed too much gas in the system.

10 minutes in the workshop (and no charge) and the AC was bloody freezing again! :)

I recall the chap @ BMW saying Halfords, Krap fit et al don't measure the quantity of AC gas correctly or something like that, I guess the shove the same volume in regardless to what car its going into?
Click to expand...

In comparison to Mercedes dealers, BMW dealers are absolutely incredible for stuff like that.

Here's hoping that Kwik-Fit will sort it out for me without any hassle. I'd vent it myself if it wasn't so bad for the atmosphere...
 
There should be a sticker somewhere on the car (usually in the engine bay) stating how much gas the AC system takes, usually it'll be a figure with a +/- tolerance.

10% over shouldn't be enough to cause an overpressure fault to the extent it's not cooling at all.

Kwik Fit should have given you a slip from the machine showing the mass of gas and volume of oil they put in, so you should be able to see if this is the problem.
 
blueboy2001 said:
There should be a sticker somewhere on the car (usually in the engine bay) stating how much gas the AC system takes, usually it'll be a figure with a +/- tolerance.

10% over shouldn't be enough to cause an overpressure fault to the extent it's not cooling at all.

Kwik Fit should have given you a slip from the machine showing the mass of gas and volume of oil they put in, so you should be able to see if this is the problem.
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I didn't get the slip, just a receipt.

FWIW the plate says 930g +/- 0.03 for the single loop cars and 1,005g +/- 0.03 for the dual-loop cars. My guess is they have massively massively overfilled?
 
Interesting that it warns you about out of spec pressure and it has also stopped working...

Is the pump running if yo can see it?
Do the fans come on with the engine cold?
 
On the same note, my fan-belt snapped on the Volvo two weeks ago, caused by the AC compressor pulley/pump seizing putting more stress on the belt. It's still not fixed yet. The irritating thing was that I knew the AC wasn't working well and it was booked in for a check-up, but it spat the belt off before my appointment :(

Compressor ~£500 new, but my garage has sorted one out cheaper, but hasn't given me a price yet.
 
They probably did overfill it in all liklihood, just after I bought the XJ6 I did the aircon myself on that, it's been quite capable of freezing me ever since. Just a thought though, it is using an R134a based system right? ...that S class is a '90s car after all, although I imagine Mercedes changed to R134a when they bought the W220 out if not on the W140 even. If I recall the older system used different nozzle sizes anyway so I doubt such a mistake could be made.
 
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Ahh, the regular "I let kwik-fit regas my aircon and now it's carped" thread appearing again...

Last time I did that I got metallic crunching noises and a £400 repair bill shortly afterwards.
 
SO I went back this afternoon, the machine was in use on another car...

... then smoke started coming out of it

... then it started to melt

...then they unplugged it and told me I'd have to take the car elsewhere.

They have tomorrow to sort this out else I will start complaining to Head Office etc.
 
Does not sound good!

Hopefully you get it sorted, usually a overcharged system would run for a short period then trip on HP, depending how over charged the system is would depend on how quick it would trip, and then would most probably auto reset.
As the cabin was perhaps cool and the ambient may of been cool this may masked the issue when they were doing the testing.
In theory the condenser and evaporator would be fine along with the compressor assuming it did not pump any liquid.

I looked at my neighbours Mondeo the weekend and this was running around 1.6 >2.0bar suction and around 10-12 bar discharge with a leaving air temp of 3c.
 
DRZ said:
SO I went back this afternoon, the machine was in use on another car...

... then smoke started coming out of it

... then it started to melt

...then they unplugged it and told me I'd have to take the car elsewhere.

They have tomorrow to sort this out else I will start complaining to Head Office etc.
Click to expand...

That's great news, that it was in use when you got there I mean :P
 
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