Air Conditioning Transient Fault?

[e220estate]

Need some better brains than mine on this....
I have a 2006 E220 with climate control which works perfectly - until the weather gets hot! In all scenarios the two leds (Climate and A/C) stay on - no blinking or extinguishing. I start the day (in the cool) - all works perfectly - I drive 200 miles (say) and it continues to work perfectly. I park up and when I come to go (mid summer afternoon) it will only blow hot, fetid air. I move off and occasionally some cool air can be felt - not cold air. And then back to blowing hot. Leave overnight (in the cool) and it all works ok again until it gets hot. A/C rad had a hole in it a year ago (emptied the R134a; flashiing red leds), replaced by a good non MB indy and was regassed - problem started then. (aside: I wonder whether some error code needed clearing - but why does it work at all, then?)
Did some research and on another MB site saw the following:
"If outside temperature (according to the car) is under 27c (80.6*F) it blows cool air. 28c to 30c (80.6*f - 86*f) it starts to struggle and above that it just blow hot air."
Is this how the A/C system works - surely not? When you really need it it just can't cope?
TIA

 

[Rory]

A thought: I wonder if the a/c is working but the car is trying to put heat in? If you put it face level vents only, is it the same on both sides?

System in my car works differently, but right vents are tepid, when left ones are pretty cold (never freezing though), If I put it on auto it's hopeless.

 

[Wolfie1]

1. Has it been recharged recently? As that can give you a symptom like that if the gas is low, other thing could be poor air flow through the ac radiator ie blocked with crud

 

[e220estate]

Thanks for the thoughts. Have not been out in the car till just recently so response is;
- AC is fully charged following the AC rad replacement I mentioned and a recent pressure test performed by me.
- facia vents were both cold when AC is working in non-Auto - no difference.
Empirical results:
- drove for over an hour with AC on 'Auto' - perfect - the fan also kicked-in when I reduced the cabin temp
- left car in sun for 4 hours, started and worked perfectly on Auto on the return
- stopped to buy some fuel, started and back to unchilled, fetid air!
- next morning worked perfectly again out and return.
I still wonder if there are error codes in memory from the total loss of refrigerant which needed the replacement AC rad. Seems this check is the next thing to do?
Brian

 

[Landie1]

it could be the evaporator icing up over time. Eventually ice forms on the outside of the evaporator and stops working. Leave it for a while and the ice melts and it works again. Is there a patch of water under the car after you have stopped for a while? Assuming you don't have a coolant leak it could be the evaporator temp sensor. A session with Star might help you out as it would show this fault. The good thing is its working until then so you know at least it does work!!

 

[e220estate]

it could be the evaporator icing up over time. Eventually ice forms on the outside of the evaporator and stops working. Leave it for a while and the ice melts and it works again. Is there a patch of water under the car after you have stopped for a while? Assuming you don't have a coolant leak it could be the evaporator temp sensor. A session with Star might help you out as it would show this fault. The good thing is its working until then so you know at least it does work!!

Many thanks for your thoughts. I left replying until I did my latest long journey - 650 miles on French Autoroutes yesterday. AC performed faultlessly all day - even the two times when I stopped for diesel it re-started. My experience of things which don't work occasionally is that they are very difficult to track down unless they are actually happening at the time. But your thought re sensor and Star will probably be my next step.
Re your thoughts on icing up. When the AC stops working it doesn't restart while driving (wouldn't the ice melt if the AC was not working?). I wonder if the compressor clutch might figure in here, somehow? Star might well show that too in its' log?

 

[Gbrowncls55]

My bet would be the exterior temp sensor, or one of the other interior sensors. I had a similar problem with my 129 . Spent thousands to no avail but then changed one sensor and all was fine (£100 all in!). I think on the 211 E class there is a mode for checking the plausibility of the sensor readings, but I dont know how to access it. Others on here pobably do. Or better still get it to a dealer and put it on star. As above if one of the sensors is giving an incorrect reading that could easily lead to icing up. Not very helpful I'm afraid , but probably a sensor.

 

[e220estate]

My bet would be the exterior temp sensor, or one of the other interior sensors. I had a similar problem with my 129 . Spent thousands to no avail but then changed one sensor and all was fine (£100 all in!). I think on the 211 E class there is a mode for checking the plausibility of the sensor readings, but I dont know how to access it. Others on here pobably do. Or better still get it to a dealer and put it on star. As above if one of the sensors is giving an incorrect reading that could easily lead to icing up. Not very helpful I'm afraid , but probably a sensor.

Thanks for that - looks like it's most likely gravitating to an errant sensor. Really need to check the OBD log, I guess.