2011 W218 CLS A/C not blowing cold

[Jonjon]

Hi,

Noticed that the A/C is not blowing cold in my CLS W218 with the analog A/C panel. The red A/C light comes on and off when pushing the button as normal and no warning messages are displayed.

Simply said, all seems well, except the air does not get colder than the outside air. When regulating the temperature for higher temperatures hot air comes through as normal.

I'd like to trigger any diagnostics and A/C reset (read anywhere that the Climatic A/C has got a diagnostics and reset mode that can be triggered by the user) but don't find any information on how to do it in the conventional A/C system that equips the CLS/W218 as a standard.

Additionally I could check the fuses for any fault related with A/C. Regrettably I don't see anywhere in the vehycle a Fuse Designation List in the boot of the car in the spare tire cavity as the owners manual indicates.

I also read that this A/C system is completely sealed and that the probability of a coolant loss is remote. Am not sure if this is really the case, but given the low mileage of the car and only having 4 years of light use it might well be an electronics/sensor issue?

Could anyone in the forum please help indicating how to perform a diagnostics/reset of the W218 standard A/C or what fuses to check for?

Cheers

 

[ras8963]

Thinking of the fuse, if you have ignition on, don't start engine, but call for cold air using AC can you hear the compressor.....I'm no expert which may be obvious from this statement, but its my initial thought>?

ATB

 

[Jonjon]

Thinking of the fuse, if you have ignition on, don't start engine, but call for cold air using AC can you hear the compressor.....I'm no expert which may be obvious from this statement, but its my initial thought>?

ATB

With ignition on, engine off when the A/C button is pressed only the red light comes on, no sound comes from the bonnet.

Anyway, aren't the A/C compressors dependent of engine rotation through a dedicated belt? In my mind the compressor should be engaged through the A/C button just when the engine is running...

 

[Jonjon]

...even with the engine running, if the A/C button is pressed I don't hear the compressor. Should this mean the compressor is currently somehow disabled? If that is the case what can I do to further diagnose with a limited set of resources?

 

[Dave Barlow]

The a/c clutch will not engage the a/c compressor if there is insufficient gas in the system.
If everything else is OK but you don't hear the clutch engage, then suspect low gas pressure.
You can buy a gas top up canister from Halfords etc. which comes with a pressure gauge. When the canister is empty, the top can be removed and the hose with gauge can be used for future pressure checks.

 

[MancMike]

I just had the same issue. The AC light would flash 3 times then go off, and alas no A/C.

The gas pressure was absolutely fine, it was the pressure sensor/switch that was faulty. I had that replaced and the system regassed and it's perfect again.

 

[DSM10000]

The a/c clutch will not engage the a/c compressor if there is insufficient gas in the system.
If everything else is OK but you don't hear the clutch engage, then suspect low gas pressure.
You can buy a gas top up canister from Halfords etc. which comes with a pressure gauge. When the canister is empty, the top can be removed and the hose with gauge can be used for future pressure checks.

Whilst no doubt well intended this is not good advice and aslmost certainly a waste of money

If there is a leak this will do nothing to detect it or allow it to be fixed.

Also, when re-filling you need to hold the system under vacuum to detect any leaks and you need to ensure that the refrigerant that you are using to re-charge is compatible.

Generally the remaing gas is removed and the amount calculated so a correct amount may be re-filled, systems also use a special oil to lubricate seals etc and this is also replaced on a proper re-charge.

 

[Jonjon]

Thanks for the replies!

So, there are no fuses that control the A/C on the W218 that I can check prior to get a gas pressure check?

 

[Dave Barlow]

Whilst no doubt well intended this is not good advice and aslmost certainly a waste of money

If there is a leak this will do nothing to detect it or allow it to be fixed.

Also, when re-filling you need to hold the system under vacuum to detect any leaks and you need to ensure that the refrigerant that you are using to re-charge is compatible.

Generally the remaing gas is removed and the amount calculated so a correct amount may be re-filled, systems also use a special oil to lubricate seals etc and this is also replaced on a proper re-charge.

The post was not intended to detect or fix a leak, but a means to eliminate all other possible causes of the fault. With the engine running, the air con on and a recharge canister connected, on raising the gas pressure, the compressor clutch will engage and the air con will work, if only for a limited time. A proper repair will involve removing anything remaining in the system with a vacuum pump, filling the system to the correct pressure with nitrogen, and checking for leaks, usually a flange joint if you are lucky. After repair, the system will need to be emptied with a vacuum pump, and refilled with the correct amount of gas, usually R134A.

 

[lexman8]

I also read that this A/C system is completely sealed and that the probability of a coolant loss is remote.

Coolant loss is quite common and can be around 10% per year.

The a/c clutch will not engage the a/c compressor if there is insufficient gas in the system.

True but the compressor might not have a conventional clutch. Many Mercs use a variable displacement compressor which is always running but can vary its output depending upon the amount of cooling required.

There is a fail-safe clutch on displacement compressors that will disengage the compressor should it seize to prevent the auxiliary belt from shredding. However, the fail-safe clutch will sometimes destroy itself in the process.

 

[DSM10000]

The post was not intended to detect or fix a leak, but a means to eliminate all other possible causes of the fault. With the engine running, the air con on and a recharge canister connected, on raising the gas pressure, the compressor clutch will engage and the air con will work, if only for a limited time. A proper repair will involve removing anything remaining in the system with a vacuum pump, filling the system to the correct pressure with nitrogen, and checking for leaks, usually a flange joint if you are lucky. After repair, the system will need to be emptied with a vacuum pump, and refilled with the correct amount of gas, usually R134A.

Your method will not elminiate all other causes though, a faulty pressure sensor etc would not be ruled out by this method. In this scenario the A/C would not work.

My point is that it is far more cost effective to take it to a specialist and, hoppefully, get a one stop diagnosis and repair options.

 

[Jonjon]

Interesting discussion with details worth knowing about, but please pardon me for asking again: what about Fuses?

Which fuses in the W218 should be checked prior to entering into deeper troubleshooting? I haven't got the list of fuses across the manual neither in the fuse box inside the boot...

 

[Jonjon]

Fuse Assignment

Glad to say, I just found the separate Fuse information together with the spare tire tools, so well wrapped there I didn't see it before.

For the benefit of whoever needs, the A/C fuses are numbers 12 and 66 (in my W218 location 66 does not get a fuse).

I also enclose scans of the Fuse list.

Unfortunately in my W218 fuse 12 is fine, there must be some other reason why the A/C is malfunctioning...

 

[lexman8]

I'm not familiar with the W218 but if you can find a fuse chart there's no harm in checking any fuses relating to the climate system. There could 2 or 3 of them.

Is the analogue aircon on a W218 a climate control system, i.e. can you set the cabin temperature you want in degrees Celsius or is it a simple cold-to-hot dial?

 

[Jonjon]

I'm not familiar with the W218 but if you can find a fuse chart there's no harm in checking any fuses relating to the climate system. There could 2 or 3 of them.

Is the analogue aircon on a W218 a climate control system, i.e. can you set the cabin temperature you want in degrees Celsius or is it a simple cold-to-hot dial?

in the W218 the normal A/C system lets you decide the right or left side temperatures (in sync or independently), at the front seats. Rear seats get the temperature of the front settings.

 

[lexman8]

in the W218 the normal A/C system lets you decide the right or left side temperatures (in sync or independently), at the front seats. Rear seats get the temperature of the front settings.

In which case I'm fairly certain you'll have a displacement compressor with just an electrical control signal going into it. This will not be fused.

Possible causes of the problem (in order) are:

1. low refrigerant pressure (and possible leak)
2. faulty pressure sensor
3. compressor failure
4. ECU fault
5. wiring fault
6. other

Once the system has detected a fault (and even after the fault is corrected) it will not turn the aircon back on until it has been reset. This is normally done using STAR.

I don't know if a reset can be done via the climate system on a W218 but on my W215 it's done as follows:

• Turn ignition on (position 2) or have engine running
• set Auto Mode on controls on both sides
• press the REST and Activated Charcoal buttons simultaneously for >5 secs
• set Auto off on left-hand side
• set Auto off on right-hand side
• set Auto on on left-hand side
• set Auto on on right-hand side
• wait a few seconds
• press REST button to exit
• turn ignition off and back on

It might be something similar on your car but BE CAREFUL. If you force a reset and the uncorrected fault is still present you can do more damage.

There is a very limited amount you can do yourself to diagnose the problem and you could end up chasing your tail and/or making things worse.

I think it would be best to get a proper diagnostic done, ideally with STAR to pinpoint the problem.

 

[alexanderfoti]

I think it would be best to get a proper diagnostic done, ideally with STAR to pinpoint the problem.

Agreed, a good indy with knowledge of AC systems and STAR will be able to resolve quickly. Otherwise you will be just guessing and throwing parts at it.