W211 E280 Air Conditioning Pressure Following Recharge

[stevenb]

Good Evening

My car is a 2006 E280 (pre-facelift)

The air conditioning was not cooling the car but there were no errors reported.

The B12/2 pressure was 3 bar with the engine off and rose to 5 bars with the engine running at idle.

I contacted the local Mercedes dealer who recharged the air conditioning.

When the car was returned the air conditioning was working well however the electric engine fan was running very fast and was very noisy. I have owned the car since nearly new and can never recall the fans running so fast.

I left the car overnight and tried it again the next morning when cold.

I measured the pressure before starting and it was 13.4 bar. When the engine was started and running at idle it was 18.9 bar. The electric engine fan immediately started to run very fast with a cold engine at idle. The fan is so loud that it is clearly audible over the road noise at 60 mph.

The Mercedes WIS states that the AC controller varies the engine fan between 0% and 100% for pressures between 12 and 20 bars. Therefore I assume that the fans are running fast due to the AC refrigerant pressure.

The dealer is currently testing the car and have stated that the normal pressure is between 0 and 30 bars so my figures with the engine off and running at idle are within spec.

Please can someone tell me if the pressure of the recharged system is correct and if so is it normal to have the electric fan running so fast with a cold engine?

Thanks
Steven

 

[LostKiwi]

Was your AC temperature set lower than ambient? If so that will cause fans to run in order to cool the condenser.

 

[stevenb]

Yes. Here are the readings for when the engine was running at idle:

B10/4(In-car temperature sensor) ----- 15.73°C
B10/6(Evaporator temperature sensor) ----- 1.42°C
N70b1(In-car temperature sensor)OCP ----- 11.50°C
Ambient temperature ----- 23.50°C
B12/2(Refrigerant pressure and temperature sensor)/Refrigerant pressure ----- 18.90bar
B12/2(Refrigerant pressure and temperature sensor)/Temperature value ----- -99°C
A9(Refrigrant compressor): Torque ----- 12
Coolant temperature ----- 41
Current consumption of component A9(Refrigerant compressor) ----- 280
Request to component A9(Refrigerant compressor) ----- 30

I think I had turned the AC temperature low on the controls in order to test the AC was working. I remember the fans slowed a bit when the AC control temperature was set to 20 degrees but still running very fast and noisy. I can test again when I get the car back.

Here are the readings before the engine was started and cold:

B10/4(In-car temperature sensor) ----- 17.58°C
B10/6(Evaporator temperature sensor) ----- 14.69°C
N70b1(In-car temperature sensor)OCP ----- 22°C
Ambient temperature ----- 19°C
B12/2(Refrigerant pressure and temperature sensor)/Refrigerant pressure ----- 13.40bar
B12/2(Refrigerant pressure and temperature sensor)/Temperature value ----- -99°C
A9(Refrigrant compressor): Torque ----- 0
Coolant temperature ----- 65
Current consumption of component A9(Refrigerant compressor) ----- 0
Request to component A9(Refrigerant compressor) ----- 0


Thanks

 

[alexanderfoti]

19bar is a bit high.

It could be overcharged. Normally when the rad fan spins up very fast, very quickly it's a good sign that the system is overcharged, especially if its not that hot inside the car.

Additionally, a blockage in the system will cause high, high side pressures.

 

[stevenb]

Thanks for the replies.

Are blockages in the system common and where are the likely points for a blockage?

Is the pressure of 13.4 bar (measured before the engine was started) also high and would excessive pressure caused by a blockage have equalised when the car was left overnight?

The engine fan is running very fast and is very very noisy.

I hope that the Mercedes dealer did not overcharge as they claim to have a machine that delivers the precise amount of refrigerant.

Thanks
Steven

 

[alexanderfoti]

Thanks for the replies.

Are blockages in the system common and where are the likely points for a blockage?

Is the pressure of 13.4 bar (measured before the engine was started) also high and would excessive pressure caused by a blockage have equalised when the car was left overnight?

The engine fan is running very fast and is very very noisy.

I hope that the Mercedes dealer did not overcharge as they claim to have a machine that delivers the precise amount of refrigerant.

Thanks
Steven

No, not common, could by anywhere, caused by faulty hoses, or failed dryer for example.

Yes 13.4 bar overnight seems high. I woukd think maybe your sensor is faulty as the pressure would definitely have equalised overnight to approx 5/6bar.

It need to be run with a set of gauges connected to see what the true pressures are.

 

[stevenb]

Thanks alexanderfoti.

A faulty pressure sensor would explain all the problems. If it had failed in such a way that it still had variable output but reading about twice the true value then it may not generate any error codes from the AC computer. However it would cause the computer to try and reduce the pressure by turning the fan up to max. It would also explain why the pressure reading from the sensor is so high after the workshop filled with the correct weight of refrigerant.

I will ask the dealer to check the pressure indicated by their refilling equipment and compare to the pressure reported by the AC controller as you suggest.

Steven

 

[alexanderfoti]

Thanks alexanderfoti.

A faulty pressure sensor would explain all the problems. If it had failed in such a way that it still had variable output but reading about twice the true value then it may not generate any error codes from the AC computer. However it would cause the computer to try and reduce the pressure by turning the fan up to max. It would also explain why the pressure reading from the sensor is so high after the workshop filled with the correct weight of refrigerant.

I will ask the dealer to check the pressure indicated by their refilling equipment and compare to the pressure reported by the AC controller as you suggest.

Steven

That sounds like a good course of action!

 

[stevenb]

Update:

The pressure sensor has now been changed and the pressure indicated before starting the engine is now lower and the electric engine fan does not run at a speed that is noticeable from inside the car. Here are my readings taken late yesterday afternoon when the car had been left in the sun for about 6 hours:

Before the engine was started (very hot inside car):
B10/4(In-car temperature sensor) ----- 62.58°C
B10/6(Evaporator temperature sensor) ----- 52.07°C
N70b1(In-car temperature sensor)OCP ----- 58°C
Ambient temperature ----- 37.33°C
B12/2(Refrigerant pressure and temperature sensor)/Refrigerant pressure ----- 10.50bar
B12/2(Refrigerant pressure and temperature sensor)/Temperature value ----- -99°C
A9(Refrigrant compressor): Torque ----- 0
Coolant temperature ----- 65
Current consumption of component A9(Refrigerant compressor) ----- 0
Request to component A9(Refrigerant compressor) ----- 0

Shortly after engine was started:
B10/4(In-car temperature sensor) ----- 52.41°C
B10/6(Evaporator temperature sensor) ----- 23.12°C
N70b1(In-car temperature sensor)OCP ----- 51°C
Ambient temperature ----- 40.63°C
B12/2(Refrigerant pressure and temperature sensor)/Refrigerant pressure ----- 18.20bar
B12/2(Refrigerant pressure and temperature sensor)/Temperature value ----- -99°C
A9(Refrigrant compressor): Torque ----- 24
Coolant temperature ----- 63
Current consumption of component A9(Refrigerant compressor) ----- 690
Request to component A9(Refrigerant compressor) ----- 70

After the engine had been running for about 15 minutes:
B10/4(In-car temperature sensor) ----- 26.07°C
B10/6(Evaporator temperature sensor) ----- 2.85°C
N70b1(In-car temperature sensor)OCP ----- 19°C
Ambient temperature ----- 40.63°C
B12/2(Refrigerant pressure and temperature sensor)/Refrigerant pressure ----- 16.60bar
B12/2(Refrigerant pressure and temperature sensor)/Temperature value ----- -99°C
A9(Refrigrant compressor): Torque ----- 24
Coolant temperature ----- 88
Current consumption of component A9(Refrigerant compressor) ----- 710
Request to component A9(Refrigerant compressor) ----- 70

Certainly extreme conditions for AC in the UK yesterday but it managed to cool the interior to a comfortable temperature.

So it looks like two problems have been corrected - faulty pressure sensor, that was reading high, and lack of refrigerant.

This combination seems to have resulted in no faults being reported, the AC controls and indicators working normally but no cooling.

The workshop reported that the equipment did not report leaks when adding the refrigerant but perhaps there is a small leak that will cause problems in the next few months or years.

Thank you very much for the help given by this forum. Thank you alexanderfoti for suggesting the faulty pressure sensor!

Steven

 

[alexanderfoti]

Excellent result, glad you got it sorted.