Heater - Hot or Warm Only ???

[Aletank]

I normally leave my heater dials in the middle on the white bits - The last couple of weeks I've noticed it blowing alot hotter than normal, even when they are turned right down it still blows luke warm, thats with the air con on.
I had the air con serviced/re-gassed about 12 months back and since then I've always left it on - so the above problem is with the air con on.
I also had the coolant changed about 12 months back too - Not sure if that would matter though.
I've just booked my car in for it's MOT next week and i mentioned it to the guy - He said it sounds like a valve is sticking but doesn't know where they are on Mercedes .
As i say its only the last couple of weeks its started like this

Any Ideas peeps
Thanks For any replies

 

[Will]

I think my old W202 did this once or twice? No air con fitted, but I remember once whilst the dial was set to the blue area it was blowing out hot air. Don't remember it happening again, but IIRC it only affected one side of the car?

Does your problem affect both side?

Cheers,

Will

 

[Aletank]

Yeah both sides are blowing warm air.

I've read from another post that there is 2 valves fitted in front of the brake master cylinder, one for each side and to try giving these a "tap". I just tapped them with a screwdriver handle but it's still the same. If I feel these or just put a finger on them, you can feel like a pumping - like a heart beat really, Not sure if that is normal or not ?? Maybe someone can check their's for me
Thanks Again

 

[Will]

Hmm - I would be inclined to think that it's pretty unlikely for two valves to fail at the same time. Obviously possible, but unlikely I would imagine.

The fact that both sides are getting hot air is the clue - if one valve was sticking, then I reckon it would be only one side hot - not both?

Perhaps whatever is controlling the valves somewhere down the line is the source of your problem?

I will see if I can find them on mine and do a quick check if I get a chance, but it doesn't sound unusual to me (at a guess!)

HTH,

Will

 

[Aletank]

I've just had my car running for 15 mins and its blowing warm even on the coldest setting. I switched the engine off then back on again - For about 5 seconds it blows cold !! then goes to the luke warm

 

[PJH]

Probably NOT this but worth checking......
Somewhere in the hand-book it says not to have the centre vents pointing up
(towards the RVM) as this will cause the system to give incorrect signals to the a/c & heater etc. The internal temp sensor is behind that little grill in the internal light unit.
Is there any change in heater output if you put the a/c off/on again ?

 

[Will]

That's not a bad idea!

You could try a bit of 'experimenting' with the cabin temp. sensor mounted in the interior light?

Will

 

[Aletank]

After reading PJH's post I've just been out and tried switching the air con off and on a few times and its definatly blowing ice cold now !! I've tried all the vent settings etc and it all cold!! and warm when i want it.
Do you think its had something to do with leaving the air con on all the time on the same setting ?? even though not on cold ? and something has stuck ?
Up untill a week or so ago I could leave the dials on the white and it was about right - but recently it has seemed hot!! and as I've said it wouldn't go cold even on the lowest setting.
I'll have to see how it goes i suppose now and maybe switch the air con off and on a few times regular.

Thanks Will and PJH for your replies/ideas - fingers crossed now !!

Anyone else had this happen or any more thoughts - please reply

 

[PJH]

Thanks Will and PJH for your replies/ideas - fingers crossed now !!

That's Ok, glad to help...

 

[Will]

Glad you got it sorted Aletank - prize to PJH for the excellent detective work!

Cheers,

Will

 

[guydewdney]

you should be able to leave the air con on all the time - when its on, and its blowing warm / ambiant air, it actually cools the air, then heats it back up (in order to dry the air). with air con off, it just warms it / lets it through.

as mentioned above - id check the temp sensor in the roof console - an easy check is to get a hair dryer / warm air gun etc and blow warm air at it - the vents shoudl change from warm to cold. even your hand temp should be enough.

guy