Astonishing what you learn! (Heater controls)

[zcacogp]

I've had my S2 just over 4 years. And done quite a lot of miles in it in that time.

And today, while sitting in a traffic jam (gotta love the North Circular) I learned something new about it!

I always believed the heating system to be rubbish. And sorting it out was one of those jobs I was saving for a weekend at the in-laws (gives me an excuse not to talk to them, y'know.) However, while playing around with the knobs (no sniggering at the back), wondering whether there was a very large leaf (or similar) stuck in it which I could blow out if I turned the blower up to full pelt, I discovered that in order to get air out of the top vents I have to move the top heater slider all the way to the left. Yes, all the way to the 'closed' position. And then lots and lots of lovely fresh air comes out of the top vents! []

This clearly bring a lot of questions to mind.

1. Is this normal? By 'top vents' I mean the ones at the top, in the middle of the dashboard (with a slider in them to direct air to the windscreen vents), and the ones at the ends of the dashboard, with the individual 'close' sliders on them.

2. If this isn't normal (which I don't expect it is), how can I correct it? I know the system is operated by servo motors, and I am guessing that swapping a couple of wires on the servo motor 'round would solve it. Off the top of your head, does anyone happen to know which wires need to be swapped? And how to get to the servo motor that controls the top vents? (The servo motor on the footwell vents was seized when I bought the car, and I rebuilt it last summer, so am fairly familiar with how they work.) Are there any easier ways to get to the wires to the servo in question - by the heater control box under the bonnet, for instance?

3. Does anyone have any good ideas for things to do while staying with in-laws?

Thanks for any assistance.


Oli.

 

[Diver944]

That's normal Oli.

The top slider with the arrow pointing up, opens and closes the dashboard vents. The lower slider with the arrow pointing down, opens and closes the foot vents. The central vent above the controls has its own slider in the centre of itself. If you have them all open you need the fan on speed 4 to feel anything significant

 

[MRGT]

ORIGINAL: Diver944

That's normal Oli.

B****r me, I never knew that. I always assumed the top slider was for the dash vents. No wonder my wind screen always takes an age to defrost in the winter [&o]

Howard

 

[robwright]

When you press the defrost button that is exactly what it does opens top flap and closesabottom flap and turns air con on. The centre vent of course can only be controlled manually. Interseting that you say you push it all the way to the left though mate to get anything out of the top vents. Surely open is all the way to the right. Think you may be on to something there Oli. Does the same happen with the footwell flap? Just wondering if the servo motor is wired in reverse or something???

 

[zcacogp]

ORIGINAL: Diver944
That's normal Oli.

The top slider with the arrow pointing up, opens and closes the dashboard vents. The lower slider with the arrow pointing down, opens and closes the foot vents. The central vent above the controls has its own slider in the centre of itself. If you have them all open you need the fan on speed 4 to feel anything significant

Paul,

That certainly confirms my understanding of the various vents, but are you sure that the behaviour I described (top slider all the way to the left for the top vents to be open) is normal? It sounds wrong to me. And, as both Howard and Rob have pointed out (but I hadn't thought of), it probably has a bearing on the way that the defrost button works. If the defrost button causes the top flap to close instead of open then the windscreen won't clear. (I haven't tested this - I'll have a go later on today.)

ORIGINAL: robwright
When you press the defrost button that is exactly what it does opens top flap and closesabottom flap and turns air con on. The centre vent of course can only be controlled manually. Interseting that you say you push it all the way to the left though mate to get anything out of the top vents. Surely open is all the way to the right. Think you may be on to something there Oli. Does the same happen with the footwell flap? Just wondering if the servo motor is wired in reverse or something???

'Zactly my thoughts. No, the footwell flap works as it should - right makes it open, left makes it close. (And you can feel more air become available out of the other vents as you close the footwell vents). Servo motor wired in reverse is exactly what I am wondering. For the first time ever, I enjoyed driving my car into work this morning with a good flow of cool air on my face - with the controls set such that it looks like the top vents should be closed.

Can anyone else (with an oval-dash model) spend a minute or to poking around with their heater controls and let me know whether my car is working the same as theirs - thanks. (Should it be relevant, mine is a pretty basic-spec S2 without air con.)


Oli.

 

[david924s]

I have a 1991 S2 without A/C if I move the top slider to the left (off) the air comes more from the vents and less from the windscreen, I always assumed the top slider is to control the air flow to the windscreen vents.

If I close off (slide to left) both sliders the air comes out more forcefully from the dash vents particularly if you put the central vent control to the bottom i.e. away from the windscreen symbol.

You can also improve your air flow if you close the passenger vent (near the door if you have no passenger obviously) as the door side vents seem to get more air flow than the central vents so closing the door side one improves the flow through the main ones.

One other thing I found with my car when I had the heater motor out to replace the wiper mechanism was that the main intake flaps (the ones that are supposed to close when you press the re-circulate button) were seized, one open, one closed so I was only getting fresh air on one side, I could not get the mechanism to work properly but I released the shut flap so at least I get fresh air on both sides. Well worth checking this mechanism if you are doing any work in this area at least a lube on the linkages before they seize like mine.

 

[zcacogp]

Clarks Garage has this page on the heating system:

http://www.clarks-garage.com/shop-manual/hvac-01.htm

It's not terribly helpful with this particular problem. (And I don't quite understand what the 'Baffle Flap' does either, although if you assume it moves with the temperature-mixing flap then it makes sense.)

David924s, it sounds as if your S2 could be working in the same way as mine. Can you confirm that you get more air out of the top vents if the top slider is slid all the way to the left?


Oli.

 

[MRGT]

Right, I've just been out for a play and found the following

With centre dash vent close (ie slider up)
Top slider full left, nothing from top vents
Top slider full right full air to top vents
with centre dash vent open (ie slider down)
Top slider full left, nothing from top vents
Top slider full right reduced air to top vents and reasonable flow through dash vents

In both the above using the bottom slider reduces the volume of air out of the top and dash vents (makes sense)

Interestingly pushing the defrost (as I call it) button, with top slider full right and centre dash vent closed, actually reduces the flow of air to the top vents. (when fan on position 4).

Howard

 

[zcacogp]

Howard,

Interesting, thanks. Sounds as if yours is working as I would expect it to. Moving the top slider to the right produces more air from either the top vents or the dashboard vents. (By 'dashboard vents' I assume you mean the long thin ones at the base of the windscreen, to clear it in the winter?)


Oli.

 

[MRGT]

Oli

Top vents= ones in top of dash
Dash vents= Ones in middle of dash
Botton vents= footwell

[]

Howard

 

[david924s]

ORIGINAL: zcacogp


David924s, it sounds as if your S2 could be working in the same way as mine. Can you confirm that you get more air out of the top vents if the top slider is slid all the way to the left?
Oli.

Yes I can confirm if the top slider is all the way to the left I get more air from the central and side vents

 

[Pastry]

i push the two horizontal sliders full left for more air into the cabin, to demist i push them full right and move the vertical slider between the center vents upwards. it does seem the opposite to what it should be, but trial and error won the day. i dont use the defrost button as it puts the heater on max and im paranoid about getting cracks in the dash from the temperature differential, although there may be no factual content in that idea. with the cabin vents open you get best airflow if you open the sunroof, and not too noisy at legal speeds.

 

[robwright]

OK this is how it works guys the windscreen vents (on top of dash) and footwell vents are both controlled by sevo motors attached to flaps. The vents in the centre of th dash are in effect connected directly to the mixing chamber.. Therefore by closing the centre vent by sliding the slider up to the windscreen sign you manually shut off that vent from the mixing chamber. By default you will get more air to both footwell and windscreen vents as ther is less coming out the massive hole in the dash. By closing the footwell flap you will again increase the air flow to the windscreen vents or vice versa. to get full demist you must either do all thsi manually or press the defrost button, whci will do it all manually. In eithercase though you must manually close the centre vent. That is why there is a little demist sign at the top of indicating this what you must do. Hope that's all clear enough. If you think that's complicated ty working on a 964 HVAC system [&:]

 

[poprock]

ORIGINAL: zcacogp

By 'top vents' I mean the ones at the top, in the middle of the dashboard (with a slider in them to direct air to the windscreen vents), and the ones at the ends of the dashboard, with the individual 'close' sliders on them.

I think we need to be 100% clear about which vents are which.

Top vents, or windscreen vents: the ones on top of the dash. Opened/closed by the vertical slider.

Face vents: the main ones, across the front of the dash (middle and both ends). Opened/closed by the upper horizontal slider (and individually by the sliders on each vent).

Footwell vents: self expanatory. Opened/closed by the lower horizontal slider.

There is a set flow of air for each numerical setting (0""4) that is divvied up between whatever vents you have open at the time.

So "¦ when the top vents are closed, more air comes through the face vents. Unless they are closed as well.

The horizontal sliders are closed when to the left and open when to the right.

So "¦ if you have the top vents open and you close the face vents, the airflow through the top vents increases. Could that be where the counterintuitive results are coming from?

I think that's right anyway. Maybe. I'm confusing myself more the longer I think about it though.

I reckon that the answer to Oli's question is that he does indeed appear to have a servo going the wrong way. Sliding the top horizontal slider to the left should close the face vents, not open them. There's a chance that what he's actually feeling is more air coming through because something else is closed off "¦ but I don't think that's the case.

 

[robwright]

The 'Face Vents' as you call them are only controlled by the vertical slider in the centre of those vents, with the little windscreen demist sign at the top of it. The windscreen vents are controlled by the top horizontal slider to operate the servo motor and flap. The side 'Face Vents' are operated by their individual on/off sliders.

 

[TTM]

The top slider controls a flap that sits above the exit in the dash from the air feed to the cabin, behind and above the center dash vents.
Slider to the left = flap oriented to feed air through the center vents and lateral dash vents.
Slider to the right = flap oriented to feed air to the windscreen.

As Paul says, this is fully normal and I may add it is even logic.

 

[zcacogp]

Peanut, Good clarification of terms. Thanks.

I'm not sure whether there is a problem or not. I suspect the key is whether the top slider controls the flow of air to the windscreen vents alone, or whether it controls the flow of air to the face vents and the windscreen vents, which is then further divided by the vertical mechanical slider in the middle of the face vent.

If it just controls air to the windscreen vent then closing it would mean there is more air available to come through the face vents. In which case the behaviour I have observed is to be expected and there is no problem.

If, on the other hand, it controls the flow of air to the windscreen vent and the face vent, which is then controlled by the mechanical slider then you would expect more air to come through the face vents when it is opened. In which case I do have an incorrectly connected servo.

Rob's post suggests that the air flow through the face vents comes straight from the main central chamber. This would suggest that the first scenario described above is correct, and I have no problem. (However, if this is the case then why is there a windscreen demist symbol on the vertical slider in the face vent? This slider should do no more than open or close the face vent and having nothing to do with the windscreen vents - apart from the fact that closing it would make more air available for both the windscreen and footwell vents.)

BUT Rob's post is backed up by this diagram from Clarks Garage:

If this diagram is to be believed, flap 5 is controlled by the top slider and the horizontal arrow below flap 5 (which isn't controlled by any flap) is the face vent exit. This is backed up further by this piccie:

... which labels the top slider as being a "defrost slide switch".

I guess the test would be to see how the positioning of the vertical slider in the face vent affects the output from the windscreen vents. And to see how the 'defrost' button (which, as has been stated, should turn the air flow as hot as possible, and only onto the windscreen) behaves - whether it opens the windscreen vent (as you'd expect if there is nothing wrong) or whether it closes the windscreen vent (as I would expect to find if I do have a servo wired up wrongly.)

More experimentation needed. Maybe I'll have a play at lunchtime; if not then this evening.


Oli.

P.S. Sorry, the diagrams have come out a bit big on here.

ETA: Rob and TTM both posted their posts while I was writing mine. Thanks for the input, chaps.

 

[robwright]

And that's it mate you have it. Now I understand fully about your post sayong moving to the left made more available at dash vents. These in fact are the 'Face Vents' as we have now defined them. Again by default closing any flap will make more air available at the other flaps unless they are also closed of course. I think??????? just think your heater is all working properly then mate given that:

FACE VENTS - THE ONES IN THE CENTRE OF THE DASH EACH WITH THEIR OWN MANULA FLAPS
WINDSCREEN VENTS - THE ONES ON TOP OF THE DASH POINTING AT THE WINDSCREEN
FOOTWELL VENTS - SELF EXPALNATORY - FOOT WARMERS OR COOLERS IF YOU ARE LUCKY.

 

[poprock]

While I wrote this up, other people posted before me and solved the whole thing. I'm posting anyway for the hell of it.

------------------

I'll use a picture to try and clarify:

The bottom horizontal slider controls only the footwell vents (indicated in green). Left for closed, right for open.

The top horizontal slider controls all the other vents: red windscreen vents plus blue face vents. Left for closed, right for open.

You then have finer control over which of those are open or closed, by using the individual sliders on the blue face vents and by using the vertical slider.

The vertical slider directs your air either up to the red windscreen vents or straight out through the blue face vents.

Basically, the top horizontal slider sends air to the blue and red vents and then the vertical slider controls the splitting of that airflow between the red and/or blue ones.

That's definitely how mine works, anyway. I've had the dash off and seen all the workings behind it.

---------------------------

So aye. Oli summarised it better.

ORIGINAL: zcacogp

I'm not sure whether there is a problem or not. I suspect the key is whether the top slider controls the flow of air to the windscreen vents alone, or whether it controls the flow of air to the face vents and the windscreen vents, which is then further divided by the vertical mechanical slider in the middle of the face vent.

The latter, on my car.

 

[zcacogp]

Oh no - now I am even more confused!

I *think* that Rob and Poprock are saying different things. Rob is saying that the top slider only controls air flow to the windscreen vents (red, in Poprocks very helpful diagram), and Poprock is saying that the top slider controls air flow to the windscreen vents AND the face vents, and the slider in the front of the face vents further divides the air flow.

Rob, Poprock - talk to each other!


Oli.