A/C Compressor not engaging ?

jasohal

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Guys,

Just had the codes read from the ECU on my 320 coupe.

A/C Compressor clutch not engaging came up..

Funny thing is I haven't tried the A/C for about 2 months now so did not really notice anything.

Anyway, I tried pressing the EC button as per normal - light goes out but no cold air coming through vents even when dials are on min temp.

There are three wires going into the plug on the compressor and have checked for +12 / earth on these pins and am getting nothing.

Does any one have any ideas/ what would be a good starting point ??
bearing in mind to demist windows effectively A/C is most desirable in this weather.

I looked at the fusebox but can't find a specific fuse/relay for A/C ?
 

prprandall51

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Most usual cause of AC not firing up is a loss of pressure in the system. There is a pressure switch in the pipework. If the pressure drops, the switch trips out and the AC will not fire up.
You can pay someone to diagnose / confirm this and have them re-gas the system or (I read on this forum) you can buy DIY re-gassing kits. Do a search on AC problems for more info.
You have to run your AC at least once a week to keep the seals in the compressor lubricated (there is an oily mist mixed in with the gas that lubes the seals as it circulates). If the seals dry out through lack of lubrication, the system will leak.
Many people think it is cheaper and better just to leave the AC on all year round than to turn it on and off when needed - a re-gas is £60 - £100, which buys a lot of fuel.
Clearly MB think you should leave it on, too. They are the only manufacturer I know who fit switches that light up when you turn the AC off, rather than the other way round.
Philip
 

marcos

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I had a very similar problem on my C-Class. I found the relay for the compressor had a dry solder joint in it. I simply cleaned it up and resoldered and was away. Might be worth checking.
 
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jasohal

jasohal

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Thanks for the replies guys.

I had the system regassed only a few months ago and have not used it as much over the summer.

As for the relay - where was it located ?

I did call Mercedes to ask them if they stocked a relay for the A/C and where it was located but as usual could not help !!
 

bolide

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Aircon

Call the guys who regassed it and ask if you can drop by in the car for them to take a look see

If it had to be regassed it's losing gas. Normally they regas with a dye in the gas so they can see leaks with a UV light. Ask if it has dye & ask them to check for leaks

Normally you'll find you have a leak in the condesnor and it needs replacing. Standard thing that seems to happens to all a/c cars at some point


Nick Froome
www.w124.co.uk
 

Stratman

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W203 C200 CDI '04Estate
My W202 had a faulty high/low pressure switch which stopped the A/C in its tracks. It is located on top of the receiver/drier and has a three wire connector on it (is the connector loose?). £80 for an A/C specialist to diagnose and replace.
 
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jasohal

jasohal

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Had a look at this over the weekend....

Managed to download the full wiring diagram for the A/C system which was a great help.

Compressor is not faulty and gas is not low. Got the compressor to come on by connecting earth to pin 10 on KLIM relay connector behind battery and bridging pin 5 and 7 ( +12V ).

Started the car and the A/C came on real cold !!

The wire giving earth to pin 10 comes from the heating control unit inside the car by pressing the EC/Drier buttons and via the low pressure switch.

Tested the switch by bypassing it - no difference.

The problem now is definitely the control unit in the car - need to take this out and inspect/clean contacts to start off with ...

Does anyone know whether the late 124 series cars only have the nuts behind the speed/dir controls to remove or have two screws above the ash tray / stereo location ??
 

Stratman

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jasohal said:
Had a look at this over the weekend....

Managed to download the full wiring diagram for the A/C system which was a great help.
Don't keep us in suspense :eek: :eek: :eek:

What's the URL for the diagram source?
 
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jasohal

jasohal

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http://www.autolib.diakom.ru:8001/CAR/Mercedes-Benz

excellent site !! covers 1987 - 97 though ....

search the first drop down for year of manufacture.

second drop down select model ( not many but many components are shared abyway )

third dropdown select system wiring diagrams

just choose diagram from there !
 

KLee

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to No.1 brand in reliability
Do you have an update as to your 'a/c control unit'? What was the cause of the problem and its solution ... I am most likely in the same boat as you.
 

Denis Thomas

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Sep 20, 2013
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Mercedes W124 E220
Hi Jasohal, I've been trying to source for climate control wiring diagram for 124 022.

I'm on a project to transfer the engine, gearbox and climate control system from a donor car sourced from Japan.

The engine and it's control mechanics work perfectly fine. Just the climate control is acting up.

When we start the car (cold engine), the compressor only comes on after 2 min or so. Then for the next 30 seconds it comes on and almost immediately off. From there, it stays on as though it started to work.

The compressor will stay on for 2 min or so, then it cuts off and does not come back on again.

To get it to restart, the car needs to be off and on. When the car has warmed up, the compressor comes on immediately, but then cuts off after 2 min.

One way to keep it cool is to press the EC button. That kind of resets the system. But it need to be frequently done .

Was hoping if you have the wiring diagram as for me to check the cables.

Thanks, Denis.
 

Yasir

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Jun 13, 2018
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C180K
I had a very similar problem on my C-Class. I found the relay for the compressor had a dry solder joint in it. I simply cleaned it up and resoldered and was away. Might be worth checking.
Hello Marcos: I am having the same problem with my C180K 2006. The compressor is not kicking in. Can you or anyone else please suggest where can I find this compressor relay and the switch if any ?. Any other suggestion will be highly appreciated. Thanks
 

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