Heater Mists up entire car

[d215yq]

Hi all. Sorry if this is a silly question but I haven't experienced such dampness and drizzle for a while. Left the car for a week in heavy rain/damp and started it and put fan on to windscreen on cold (i don't liek to use heaters til engine warm)...all good and no mist at all. Then after a few miles put heaters on and suddenly windows filled with mist, so bad I had to stop. It then cleared it after a couple of mins and all good.

Left it another cold drizzly few days and got in car, no mist upon entering but this time started car with heaters on and within 10 seconds mist everywhere, again clearing with blowers.

Is this just normal as heaters evaporate damp water or does it suggest a problem. Am I right in thinking no mist upon entering the car means cabin doesn't leak but maybe water is collecting in a cabin filter, if this even has a filter (it's got factory fitted A/C). What do you guys think.

 

[MIW615]

Sounds like the front scuttle water drain holes are blocked and you have water in the heating / fan area.

Do a search on water drains - loads of advise there

 

[SL63 Mark]

^ +1

 

[d215yq]

Centre drain clears perfectly and straight out onto the floor above the transmission. Shame the two side drains at the side of the windscreeen are pretty much blocked solidly.

Nevertheless, is it not the centre one that affects the heater? Or is there another centre drain in addition to the main centre one?

Thanks again, Ben

 

[turbopete]

it could also be the heater matrix having a slight leak.

personally id not worry about using the heater straight away as thats what its designed for. its a DEMISTER after all, and it wouldnt be as effective in thie damp weather we are having if it was blowing cold. also if you have aircon, USE it.

 

[MIW615]

Centre drain clears perfectly and straight out onto the floor above the transmission. Shame the two side drains at the side of the windscreeen are pretty much blocked solidly.

Nevertheless, is it not the centre one that affects the heater? Or is there another centre drain in addition to the main centre one?

Thanks again, Ben

I would make sure all drains are clear before going any further

Had this problem on three of my previous Mercs and every time it was down to blocked drain tubes

 

[star]

Or your a/c isn't working correctly or its turned off.

 

[onefortheroad]

Use air con. Make sure recirc air isn't on. The thermostat will be jammed shut anyways until engine is hot enough so using the blowers wont make a jot . if you have a demist button use it .set temp to 24 and engage auto climate control.

 

[EmilysDad]

I've no idea on this specific car, but on my previous car (Vx Omega) there were exhaust vents in the boot area that could easily get blocked with the kind of gubbins we all tend to carry in our car ie the air needs an exit from the cabin to give an airflow through it.

 

[d215yq]

Thanks for the inputs...car is 1987 W124 with A/C which has never worked in my ownership (well the light on the panel lights up but never gets cold air into the cabin).

I'll endeavour to unblock the side drains anyway, any tricks for that?? They're still blocked after much poking/soda crystals today.

It certainly blows hot air as soon as car is started and this immediately has an effect on the windows. Does this car have some cabin filter to change I could try. Could well be heater matrix leaking as car sometimes looses a little coolant but this is intermittent and doesnt seem to be heater use related

 

[LostKiwi]

If it's the same as the r129 the cabin filter is in front of the windscreen under a plastic cover.

 

[hotrodder]

Is the A/C button marked with A/C or a snowflake or is it marked EC? Can't remember when MB changed things but EC stands for economy i.e. it works backwards and default is aircon switched on, red light denotes that it's switched off. Obviously the aircon won't do anything if all the refrigerant has escaped but when it is working it's independant of temperature... will cool the air if necessary/interior is hotter than heater setting or dehumidfy heated air if the demist/dehumudify button is pressed

The heater always water in it, granted if it's weeping ever so slightly it'll be more prone to do so when in use but in either case the 'sweet' smell of antifreeze should give the game away... when i've owned something that had a weaping heater (i.e. not leaking enough to soak the carpets) you'd often get a whiff of coolant through the vents briefly after starting the engine when the cars been parked up for a day or two

Am I right in thinking no mist upon entering the car means cabin doesn't leak but maybe water is collecting in a cabin filter, if this even has a filter (it's got factory fitted A/C). What do you guys think.

I'm 99% sure only the very last 124s got a cabin filter, my '93 with factory Behr aircon definately has no provision for them and as said when fitted they live in just front of the screen under the heater intake grilles. Googling w124 poolen filter will get you pics and vids and show what an afterthought they were

No misted windows entering the car doesn't mean it's not damp inside for whatever reason. Just that the air inside isn't warm enough for moisture to condense on the cold glass. As the interior warms up this changes whether it's damp clothes from being out in the rain prior to getting in the car or a damp interior with the car parked up on a sunny day. Even a cold but sunny day. Big giveaway that a car is leaking/wet inside is windows that'll properly mist up an hour or so after parking up

As said clean the drains first, compressed air is often great for this, without a compressor you want something reasonably flexible but not too stiff or sharp to poke through them... small dia plastic tube for windscreen washers, old curtain wire etc

 

[Essel]

Without airconditioning, the only way to dry the car out is to heat up the air to push water into the vapour phase...

When the car starts up, is the air actually hot? The air in my car takes about 15 minutes to get hot (when the engine reaches 80C).

 

[d215yq]

Thanks, the car has two buttons: EC and snowflake. I always have the red light on EC as on snowflake it never made the air cooler when hot so assume its broken. I haven't looked into this further as its my first car with A/C and even in Spain I really don't like A/C, and given the state of the car in general I'm assuming a simple regas won't solve it.

The car has zero mist/water inside, so much so that in cold/rain the fan can be on 1 or 2 and directed at screen on cold and it keeps it clear perfectly. Upon switching the heater on (for my benefit rather than to clear the screen) within 5 seconds the windscreen/side windows/wherever the fan is directed suddenly become very misty. So much so it's dangerous.

If I start the car with the heater on within under 30 seconds the windows have gone from clear to misty, thus having to wait a few minutes to clear it. The heater has lukewarm air coming out after about 30 seconds and gets warm quite quickly. I can't smell any coolant although one thing I noticed on my long drive a week ago was that when the heaters were on a long time a burning dusty smell seemed to enter the cabin (though no coolant smell).

Its the sudden filling of vapour when heater is switched on that makes me think there is definitely some water where it shouldn't be. Off out for another drain unblocking session to see if that improves it but as before it's only the side windscreen drains and fuel filler that are blocked.

 

[onefortheroad]

check that the recirculating air button isn't pressed , is the only advice I can offer up . either that or the flaps/cables/motors that control airflow are jammed .

 

[d215yq]

Finally, side scuttle drain unblocked... about 8 inches of solid mud finally dislodged! Using car daily now and even in frosts no more condensation from the heaters and little need to use the fan even

 

[DREAMER NO2]

Most cars i have driven with A/C the windows condensate , you will have to use the Aircon to shift it

 

[LostKiwi]

Warm air can carry far more moisture than cold air. If you have condensation you need to do three things.
1. Get the incoming air as dry as possible. Aircon does this very well as it dehumidifies. Blocked scuttle drains hinder this.
2. Warm the air up. This enables any dampness in the cabin to transfer to the warmed air.
3. Get rid of the warm moist air as quickly as possible. This is normally accomplished through vents at the rear of the car. It can help to open windows slightly for this reason if you have a lot of condensation to remove. Blocked rear vents can hinder getting rid of warm moist air.

 

[Parisien]

Had a quick search, didn't quite find what I was looking for, car some one tell me the locations of front water drains, is there a diagram....having same misting up issue as d125yq on my 300ce 1990.


P

 

[hotrodder]

There's one at each side of the lower corners of the windscreen and two in the middle- directly below the wiper there's a small grille in the heater airbox intake which pulls out (on later models at least) revealing the drains

http://www.w124performance.com/service/Index/Groups/60Paint.htm has location of water drains for most models from the era and there's pics instead of bad drawings in many of the wiper servicing write ups for example http://www.marekv.ee/MB/MonoWiper_removal.pdf is for the earlier/pre facelift wiper, the drain is shown in pic #4

If the trim at the base of the screen, the wiper and the heater airbox haven't been disturbed for eons there's likely a sizeable compost heap hiding under there