Air Con blowing hot & cold W203

[Barticus_UK]

Hi all, after a week of making strange noises ( hissing from behind the dash ) my climate has finally died! It now blows freezing cold on the passenger side and ambient / warm air on the drivers side. Has anybody any experience of this? My car is fitted with the upgrade climate control ( from the factory ) if this makes a difference. I assume the compressor / gas / heat exchanger are ok as the passenger side responds to the temperature called for by the relevant control, and the distribution and fan speed selectors all work ok both in manual and auto on both sides. It seems to just be the drivers side temperature regulation that has packed up.

Any ideas - please?

Regards,

Martin.

 

[recycled]

Duo valve fault?

 

[television]

Do a re set

203

To reset heater flaps and actuators

Switch on ignition.

Press recirculated air and defrost buttons on control panel together for longer than 5 seconds.

The LED's in the defrost and recirculated air buttons flash alternately.

Wait until the LED's stop flashing (approx 30 sec) system set to defrost LED on.

Switch off ignition.

After 40 sec re start engine

 

[Barticus_UK]

Thanks for replying. I have heard the term duo valve several times whilst searching this forum but am not sure if it applies to the 203? Any one know where it / they are? Or what to do if you find them?

Many thanks,

Martin.

 

[Dieselman]

I think television is correct. If it was the duo valve you would be rather hot by now.
It sounds like the air flaps are confused.

Having said that there is only one air con evaporator for both sides. Try turning the temperature on the drivers side both right up and right down to see if this shuts off the warm air.

 

[Barticus_UK]

Hi, thanks to all for replying. I shall try a reset a soon as I get chance! Will post my results, good or bad.

Again, many thanks for the sugestions.

Martin.

 

[television]

I have known the re set to work well on 5 cars now

 

[DansSlk]

Ditto on the reset.

Good place to start

 

[Barticus_UK]

Thanks all for the advice. No joy with the reset though - it worked as described but it's still blowing warm on the drivers side. Blows hotter when you call for heat (i.e. set at 22+ °c ) so the temperature regulation seems to work ( apart from cooling ) if thats a further clue?

Regards,

Martin.

 

[DansSlk]

Leaning towards the duovalve then mate.

 

[television]

http://www.detali.ru/cat/oem_mb2.as...648716.649&CT=F&cat=69J&SID=83&SGR=180&SGN=05

I think its item 38

 

[Dieselman]

Leaning towards the duovalve then mate.

Not sure about that. The valve is operating allowing more and less water to flow. The air tmperature felt is just he ambient temperature, which due to being warm feels hot compared to the air conditioned side.

Try turning off the aircon and see if the temp is the same both sides, I suspect it will be.

This then points to either a sensor problem or an air flap motor stuck.

Does the W203 even use a Duovalve, it only has one heater radiator, doesn't it?

Look at item 200

 

[Diesel Benz]

On another forum experts claimed that low freon (what ever it is today) could cause cold on one side. I never understood how could that be but they were serious. The heater core is common anyway, I don't see either that causing hot/cold on one side. Any thoughts here, and how old is the W203, could it have leaked some "freon".

 

[Dieselman]

Possible and maybe the hissing noise is either escaping refigerant or the expansion valve.

 

[DansSlk]

Yeah it only has the one exchanger but you still get the control valve.

I would expect the noise of a jammed flap to be obvious especially during the reset, the hissing noise does lean toward gas but that would be a major leak and the system would probably have shutdown by now.

 

[Diesel Benz]

Yeah it only has the one exchanger but you still get the control valve.

I would expect the noise of a jammed flap to be obvious especially during the reset, the hissing noise does lean toward gas but that would be a major leak and the system would probably have shutdown by now.

If you are referring to my comment about a single exchanger, I meant how could a problem in the mono valve make one side hot? Perhaps after all the same as the claim on the refrigerant, which I did not understand either.

The flap issues as referred previously would sound absolutely logical but the reset at least did not seem to help on this car.

The evaporator always makes some "hissing noise" as its job is to evaporate the liquid from the compressor but I assume this time the noise is significantly stronger than normal. Could low refrigerant also increase the noise?

I would assume a hissing noise from a leak being quite short in time, if it was leaking so much that one could hear it, it should not have 134a for too long time then, would it?

 

[1998K]

I'm not an expert but I'd like only to provide my litte help, I'm quite sure that duovalves are not installed on W203. I've read this on a Mercedes document somewhere.

 

[BlackC55]

The cause is probably one of two things.

1. Low on gas
2. Blend flap stuck.

A test on a star will pick it up easily. The stuck flaps always bring up a code.

 

[miro]

Possible and maybe the hissing noise is either escaping refigerant or the expansion valve.

Yes, if the gas pressure is too low the coolant evaporator in the heater box will only have enough gas pressure to partially cool. Then the temp sensor on the right side will be getting the wrong readings. So its mixer values will be set to cool because the right side of the evaporator is warm and the left is cool.

So if the reset does work be careful with running the AC at all until such time as the pressure level is checked.

The level can only be checked if the gas is removed. Weighed in grams and then installed to the correct MASS. As far as I know it takes 750grams as liquid under pressure.

The hissing is the low pressure of the coolant (gas) hitting the pipes as it streams into the evaporator past the TX valve (Duo valve).

The TX valve only ever dies if the gas pressure (mass) is so low that the compressor shreds itself and the metal flies into the valve.

To replace the TX valve you need to remove the wipers, windscreen water catcher, the wiper motors, centre console, dashboard, crossbar and the heater box. But it isnt that anyhow.

 

[miro]

The cause is probably one of two things.

1. Low on gas
2. Blend flap stuck.

A test on a star will pick it up easily. The stuck flaps always bring up a code.

I recently did a mad thing and converted 580 into 581 on my car. I notice the blend flap is in fact 3 flaps driven by one motor. There is an extensive set of cogs and wheels held together in place with several screws. It sits vertically on both sides of the heater box.

I also saw that it has liberal amounts of long-life grease on the friction surfaces of the more complex cogs.

So my questions is ..... what do people usually when faced with a stuck motor. How do you service this area in a workshop environment ?

I learned a lot about this assembly by tinkering with my own heater box on a table. But I imagine that most workshops work on the problem in-situ.