Heating issues - W202, OM605

[spock500]

Hi all,

I think something is stuck within the heating system, symptoms as follows;

Hot air always through the side and middle dash vents no matter what setting the hot/cold controls are set to.

Takes ages to switch from cold to hot through the screen and floor vents even when hot, sometimes I don't think it switches at all as I ma at the end of my journey before it does.

Any ideas?

Non a/c model

 

[spock500]

Looks like I may have started this thread in the wrong section.

Had a hunch about 'duo valve' which produced these results

http://www.mbclub.co.uk/forums/howto/26888-howto-clean-duovalve-w210.html

http://www.mbclub.co.uk/forums/interior/91688-w202-duo-valve.html

 

[Dec]

My limited knowledge, for what its worth is as follows;
You have dual heating so 2 valves, one valve for the passenger side, one valve for the driver side, each sides temperature is controlled by a thumb wheel.
At the duo valves, one tube with hot coolant goes into the duo valves and 2 tubes come out the other side, one for each side of the cabin.

If one or both thumb wheels are turned to Blue then power is supplied to the duo valve/s, this closes the valve/s preventing hot coolant reaching the heater and so you have cold air in the cabin.
If one or both thumb wheels are turned to Red then power is not supplied to the duo valve/s, this opens the valve/s allowing hot coolant to reach the heater and so you have hot air in the cabin.

If a fuse fails or there is an electrical fault and no power reaches the duo valves then the duo valves remain open so you have hot air, all the time.

The centre vent, when it is opened via its thumb wheel supplies cold fresh air only if you don’t have air con.

So, if you turn both thumb wheels to Blue and after you get the car up to normal temperature, the 2 tubes going to the heater should be cold, if thease 2 tubes are hot then the duo valves have failed, either stuck open or aren’t getting any power.

Turning a thumb wheel from hot to cold will not give instant cold air in the cabin, it will take several minutes for the hot coolant in the heater to cool down, depending how fast you are moveing or if the blower fan is on full blast or not.


Dec

 

[spock500]

Many thanks for the detailed and helpful reply Dec,

So as a basic test the two window side vents should if working right blow hot or cold according to the tempo controls with the centre one only blowing cold.

Will post back how I get on over the weekend.

 

[martin_a]

I had the same thoughts about mine at first, does seem to take a few minutes to go cool from hot and the wheel doesn't seem too accurate on temperature.

More concerning is the fact that the heater is like baby's breath on the windscreen, even at high.... does anyone know if there is a filter in ther somewhere which might be blocked?

cheers,

m.

 

[Dec]

Never heard of a filter for that and doubt that there is one. A poorly maintained heating system can clog up and reduce the flow of coolant in the heater matrix or perhaps the duo valves might be sticking and not fully opening, resulting in your symptoms.


Dec

 

[Alps]

defo sounds like duo valve stuck, theres a thread somewhere on here on how to fix it.

 

[martin_a]

Cheers guys, the heater works and the fan does make more noise, just don't seem to be a high airflow (hot or cold). i suspect it needs a good clear out somewhere but will check out the valve action.

m.

 

[Nasco12]

Never heard of a filter for that and doubt that there is one. A poorly maintained heating system can clog up and reduce the flow of coolant in the heater matrix or perhaps the duo valves might be sticking and not fully opening, resulting in your symptoms.

Pollen filter, no? Made a big difference when I changed mine.

 

[Dec]

I was thinking coolant filter, that’s worth investigating if the volume of air being shifted seems low, good thinking batman... index

Dec

 

[spock500]

Do you know if there are pollen filters on all W202's or just the later ones?

Btw, did't get around to the due valve this weekend due to relatives visiting who are not very car maintenance minded

 

[Stratman]

defo sounds like duo valve stuck, theres a thread somewhere on here on how to fix it.

Percussive maintenance has been successful for some

 

[martin_a]

I was thinking coolant filter, that’s worth investigating if the volume of air being shifted seems low, good thinking batman... index

Dec

That's exactly it! Just back after the bank holiday (900 miles in 3 days no issues whatsoever) so will have a go at that later.

thanks all.

m.

 

[Riablo]

Blower Regulator or Valve

Just noticed, that my w202 (1997 C240) A/C blows air on all settings, no matter, if it is on or off.

If blows, even when the car keys are out and the car is parked.

Any suggestions? Should I check for blower regulator? Can it be fixed or buying a new one is the only option?

No I only disconnected battery for the night, being afraid that it would discharge it fully.

Thanks

 

[boredoutofmynut]

I know bit late but think might help some one
if blower is on constantly, the lead has been put on wrong way round....on blower motor!!!!!!!

 

[zoob98]

if it runs all the time its the regulator because no resistance on the bottom of blower fan passengers side red and blue wires and 3 pin plug if its not spinning its the fan motor