Heres a problem for you?

[TheGrocer]

Visited the MB dealership today with the following problem:

A/C not as cold as it used to be and the W211 is blowing hot air out of the rear passenger vents even when its set to LO. (My MB has the electronic A/C with seperate controls in the back)
Now I tell the MB guys this and they assume the system needs a re-gas as the pressure is low. No other problems they tell me and they re-gas the system and send me on my way.:)

3 miles down the road I turn around and head back to the MB dealership to explain the same symptoms exist!:confused:

Have you checked the thermostat in the back I ask?... 1 hour later and they tell me all is ok with the thermostat and that the pressure has dropped again and their must be a leak.

We need the car for a couple of days to check the system for leaks using Ultraviolet Testing:eek:

The car is going back in on the 7th July for a few days to test for leaks however why would hot air be comming out the back passenger vents when the system is set to LO on all settings?:confused:

Im guessing the air temp is about 28C when the front is cool. Whats going?

[Diesel Benz]

If there is a leak in your AC system, that is an independent issue. The problem with heat for the rear is the heat exchanger shutoff valve.

Tell your workshop guys to read AF8340P3001A.

[Dieselman]

Turn off the A/c it will probably blow cold then.

The heat is applied to after heat the air once it is chilled by the A/c because the A/c makes it too cold.

Hmm, use energy to cool the air then use energy to re-heat it to a correct temp.

[Diesel Benz]

Turn off the A/c it will probably blow cold then.

The heat is applied to after heat the air once it is chilled by the A/c because the A/c makes it too cold.

Hmm, use energy to cool the air then use energy to re-heat it to a correct temp.

Heating is using the energy that would otherwise be lost via the radiator. One cannot get cool air without energy, old AC-systems did cool down the air to a fixed low temperature which means excessive energy consumption. Modern AC-systems cool down the air only sufficiently, a bit of heating is still applied to reduce the humidity to a safe level (to avoid condensation at the windscreen and other places.

[Dieselman]

Heating is using the energy that would otherwise be lost via the radiator.

There is no such thing as free energy though. That heat has been lost by the engine and has used fuel to make it and reduced the efficiency of the engine as a result.

[Bobby Dazzler]

There is no such thing as free energy though.

Oh, I dunno. Since tapped into the neighbour electricity our bills have come right down. :D


On a serious note, where do the warm and cold feeds combine - could the connector have worked loose?

[BlackC55]

Oh, I dunno. Since tapped into the neighbour electricity our bills have come right down. :D


On a serious note, where do the warm and cold feeds combine - could the connector have worked loose?

Its a motor controlled flap.

[jaymanek]

didnt I read somewhere that the rear has almost a completely independent A/C system, so there could be a leak in the pipework for that... if they are saying pressure is low then the gas must have gone somewhere...

[Bobby Dazzler]

Its a motor controlled flap.

Sorry I meant electrical connector that controls it. :o

[Diesel Benz]

There is no such thing as free energy though. That heat has been lost by the engine and has used fuel to make it and reduced the efficiency of the engine as a result.

This is totally off topic but: of course the heat dissipated by the radiator is not free energy as such, it has been produced from fuel as you say. But the point is that, at typical (even mostly at extreme conditions) the radiator would dissipate heat even when the interior heating is taking part of it. The result being: the engine spends the same amount of fuel independently if part of the produced heat energy is used for the AC or not. If it is not used by the AC, it is lost by dissipating it from the radiator.

The AC compressor is another thing, I was just claiming that you don't lose the energy twice when first cooling the air and warming it up afterwards. But you can save energy if you don't cool the air more than sufficiently.

[Diesel Benz]

The 4-zone AC does not have a completely separate AC unit for the rear (the W221 would have). The problem with hot air at the rear typically comes from the fact that the AC system opens one flap to increase air flow when high cooling power is needed. Now if he heat exchanger shutoff motor does not completely close the hot water circulation in this case, it allows hot air entering mainly the rear nozzles. I would at least check that the shutoff valve is working properly.