Sensor in sunroof switch surround (w126 / w124)

[Classic_car]

Does anyone know, if the heater will still blow hot if the sensor in the sunroof is disconnected? Is the sensor vital for cars without air-conditioning, what exactly does it do?

The pipe going down the A-pillar, is missing on my car and I have no heat from the heater. I am trying to flush the matrix (think i've moved some crud, elsewhere in the system now ) and have, at last, got the in and out pipes from the matrix to get hot, but still not a jot of heat from any vents. The duo-valve looks ok and I thought the default setting if the duo vale breaks, is hot air rather than cold (i.e. it is open if disconnected and letting coolant into the matrix)?

Car is 1988 300se, without aircon. This is starting to stress me as it's getting pretty cold and the windscreen keeps misting up now . Anyone able to offer some advise?

 

[jaymanek]

That is only used if the car has climate control... What that does is suck air in from the cabin into a chamber where its temperature is measured, then the climate control adjusts its temperature according to the desired temp you have set.

If both the pipes are hot I cant think why you are not getting warm air...

 

[Biglips]

I'm no expert but when my duovalve went I got nothing but cold air. I remember it well because I was on dartmoor and it was snowing. We were freezing!!!

 

[Classic_car]

Thanks for the reply. My car has a re-circ button, but no air-con, so I assume it does not need the roof sensor at all then? I've removed the motor as it was just doing nothing as there was no pipe in the a-pillar.

The matrix in and out pipes were always cold, i've now flushed it several times and cleaned out the duo-valve. Now the the matrix in and out pipes are very hot indeed when the car is warmed up, but, it's made no difference at all, there is still only stone cold air coming from vents. It makes no sense to me!

 

[jaymanek]

I cant understand why you would have the motor and no climate! I know they put the pipe there on all cars but the motor is usually only there on cars with the push button climate.

 

[312 Sprinter]

Does anyone know, if the heater will still blow hot if the sensor in the sunroof is disconnected? Is the sensor vital for cars without air-conditioning, what exactly does it do?

The pipe going down the A-pillar, is missing on my car and I have no heat from the heater. I am trying to flush the matrix (think i've moved some crud, elsewhere in the system now ) and have, at last, got the in and out pipes from the matrix to get hot, but still not a jot of heat from any vents. The duo-valve looks ok and I thought the default setting if the duo vale breaks, is hot air rather than cold (i.e. it is open if disconnected and letting coolant into the matrix)?

Car is 1988 300se, without aircon. This is starting to stress me as it's getting pretty cold and the windscreen keeps misting up now . Anyone able to offer some advise?

Have you checked all the fuses are nice and clean. If there is a bad contact the duo valve will just sit at the point it was last powered up at.

 

[Classic_car]

Have you checked all the fuses are nice and clean. If there is a bad contact the duo valve will just sit at the point it was last powered up at.

I will check the fuses. However, i've removed the duo-valve several times and unless I am mis-understanding, it looks like it is always open, unless the magnets are activated? The hot pipes to and from the matrix seem to confirm that it is open also.

 

[Classic_car]

I cant understand why you would have the motor and no climate! I know they put the pipe there on all cars but the motor is usually only there on cars with the push button climate.

It is strange, I agree. I am totally at a loss with this problem. I thought, in desperation it must be something to do with the roof sensor, as the matrix pipes are both hot. I've looked on the Russian VIN de-coder site and my car never came with Climate or Air-con, but the motor was sitting there behind the glove box, weird!

 

[Classic_car]

Just replaced all the fuses in the box by the duo-Valve, problem still there. Car warms up to 89ish, heater hoses all very hot to the touch, no warm air at all from vents. Cannot fathom what could be going on. No coolant leaks anywhere, heater hoses seem a bit pressured, but not solid, assume that's ok? Help someone pls, can't really use the car like this in the winter months!

 

[312 Sprinter]

Just replaced all the fuses in the box by the duo-Valve, problem still there. Car warms up to 89ish, heater hoses all very hot to the touch, no warm air at all from vents. Cannot fathom what could be going on. No coolant leaks anywhere, heater hoses seem a bit pressured, but not solid, assume that's ok? Help someone pls, can't really use the car like this in the winter months!

Is the vent control actually working? I recently had a problem with the E220 I did where when I turned the air control I cold hear the air changing direction but it wasn't blowing.

If you turn the fan on full and switch it to demist you should be able to feel the airflow strongly with your hand.

In my case the collets on the cables behind the control had come loose.

 

[Classic_car]

At the moment I have the vent control directing air to the windscreen. I can feel plenty of air blowing, but it is totally cold :-(

Tried the temp controls on cold, to see if it is working in reverse, but no change.

I don't know what to do next :-(

 

[Classic_car]

At the moment I have the vent control directing air to the windscreen. I can feel plenty of air blowing, but it is totally cold

Tried the temp controls on cold, to see if it is working in reverse, but no change.

I don't know what to do next

 

[jaymanek]

Id still suspect the duo valves...

If the valve is closed the warm water is directed to by pass the heat exchanger and if its open the warm water is sent to heat exchanger.

 

[312 Sprinter]

At the moment I have the vent control directing air to the windscreen. I can feel plenty of air blowing, but it is totally cold

Tried the temp controls on cold, to see if it is working in reverse, but no change.

I don't know what to do next

It could be something as silly as an airlock or an internally collapsed hose. If it were me and I'd tried the obvious stuff, and it sounds like you have, you need to ascertain if water is actually capable of flowing through the heater core.

I once spent ages trying to figure out why a Volvo I serviced wouldn't produce any heat. Turned out someone had the engine out and swapped over the flow and return hoses when they put it back together.

 

[Classic_car]

Id still suspect the duo valves...

If the valve is closed the warm water is directed to by pass the heat exchanger and if its open the warm water is sent to heat exchanger.

Is it a case of one plunger down, one up to direct the heat through the matrix? I assume not, I was guessing that there are 2 plungers as there are 2 temp control wheels (driver side and passenger side)

When I took it apart, there were 2 plungers inside 2 magnets. As far as I can see, the plungers are sprung, so that they are always up (open), inside the magnets, by default.
I think they are only closed, if the magnets are powered, then the plungers would be repelled by the magnets and forced down, closing the off pipes. If that is the case, then water must be going through the matrix, mustn't it?

Have I got this wrong? Looking at it, it seems the only way it can work to me, but I would be delighted to be wrong as that would solve my problems!

 

[Classic_car]

It could be something as silly as an airlock or an internally collapsed hose. If it were me and I'd tried the obvious stuff, and it sounds like you have, you need to ascertain if water is actually capable of flowing through the heater core.

I once spent ages trying to figure out why a Volvo I serviced wouldn't produce any heat. Turned out someone had the engine out and swapped over the flow and return hoses when they put it back together.

I am right in thinking that the flow hose is the one on the header tank side (driver) of engine bay and the return is the one that is on the ABS pump side (passenger)?

I'm starting to think it must be an air-lock (is there a special trick to remove these on the m103?) or the majority of the matrix is blocked, but then both hoses get really hot, so there must be some flow of water, yet the air from the vents is stone stone cold

I remember having a similar nightmare with a TVR S a few years back and it was an air-lock, the system was very hard to bleed on that car and took me 3 attempts to get it right

 

[Classic_car]

UPDATE:

It appears that very little water is getting through the matrix, probably there is air in there and it is also mostly blocked. There is enough air or water to make the in and out pipes hot, but clearly the flow is a dribble and not enough to produce heat at the vents.

So, i've tried holts radflush twice now and it still seems mostly blocked, anything else I could try?

Also, is the matrix flow hose the one on the header tank side (driver) of engine bay and the matrix return the one that is on the ABS pump side (passenger)?

 

[ianrandom]

I can confirm all the climate versions have the temp sensor and little motor behind the glovebox. Both my 420's are non-pushbutton climate and they have them. Its very odd that pipe isnt there? Your twin temp wheel version still needs to sense the temperature doesnt it? One 420 has aircon and has the little motor, the other 420 doesnt have aircon and still has the little motor.

On the subject of duovalves, on another site i was reading how this person tried everything, but in the end discovered it was the actual magnet parts of the duovalve that had got weak, which were preventing them from working properly. Just a thought. His had looked fine and he had good diaphrams but it wasnt them.

 

[Classic_car]

I can confirm all the climate versions have the temp sensor and little motor behind the glovebox. Both my 420's are non-pushbutton climate and they have them. Its very odd that pipe isnt there? Your twin temp wheel version still needs to sense the temperature doesnt it? One 420 has aircon and has the little motor, the other 420 doesnt have aircon and still has the little motor.

On the subject of duovalves, on another site i was reading how this person tried everything, but in the end discovered it was the actual magnet parts of the duovalve that had got weak, which were preventing them from working properly. Just a thought. His had looked fine and he had good diaphrams but it wasnt them.

Hi Ian, thanks for posting. I probably should have explained better, my car did have the pipe in the a-pillar originally, but it had degraded to such an extent that it had been removed by previous owner. So, there was a pipe, sensor and motor. But, the Russian Vin site does not mention Climate and my car just has 2 dials, a recirc button, but no other buttons, so I am assuming the car does not have climate (it certainly does not have aircon), so the pipe, sensor and motor are not needed - correct?? If they are needed then, it could be problem solved , but I cannot see why they are needed, in a car without climate or aircon

The magnets may well be broken or weak, but looking at the duo-valve, it seems to me that if it was dis-connected electrically or magnets were weak, it would fail 'open', therefore water would be directed through the matrix? As I understand it, the duo-valve works by a current activating the magnet to repel the plungers, that then seal off the pipe work to the matrix, therefore, when there is no power to the magnets, or they are weak, they do not repel (force downwards) the plungers and so the pipes to the matrix are fully open?
Does that make sense? This is ruining the car for me, as in cold weather I will not be able to use it

 

[kth286]

But, the Russian Vin site does not mention Climate and my car just has 2 dials, a recirc button, but no other buttons, so I am assuming the car does not have climate (it certainly does not have aircon), so the pipe, sensor and motor are not needed - correct?? If they are needed then, it could be problem solved , but I cannot see why they are needed, in a car without climate or aircon

that generation of Merc had very good and precise cabin temperature control - whether it had aircon or not.

You can set the temperature (between a lower limit and an upper limit) at a particular setting, and it would be very precisely controlled inside cabin irrespective of what was happening outside the cabin.

I have the sensor in the overhead lamp (and pipe and motor) in my 124 model, but have no aircon.

You can occassionally hear the temp controllers adjusting themselves in the background.