Cabin heater temperature control lever stuck

[Peter Bristow]

What the title says really - the temperature control slider or lever that sits just above the air distribution control buttons in the dashboard seems to have seized up. There is a tiny bit of movement, but essentially it is stuck and I certainly don't want to risk breaking something by trying to force it to move.

I've taken a look at the exploded diagram in the parts book in the hope that that might show what the visible slider knob is connected to 'behind the scenes', but sadly it was of zero use in that regard.

Could anyone explain the mechanism by which the slider lever works to control the temperature of the incoming air? Presumably it acts on a means of controlling the amount of hot engine coolant passing through the heater matrix, but it would be helpful to know just how it does this.

And has anyone experienced a similar stuck slider before and successfully fixed it? If so, how? (And how much of the dashboard was it necessary to take apart?!)

I don't think it matters much for this issue, but the car is a Gamma 2500 berlina, built in 1978.

All helpful comments gratefully appreciated. Thanks in advance!

[Theo]

Make sure the push buttons are not in the off position as that locks the slider. Try pressing the RISC button and see if the lever unlocks.

Temperature is controlled by a flap which varies the amount of fresh air mixed with heated air through the matrix. There's also and on/off water valve in the engine compartment near the bulkhead controlled by vacuum.

 

[neromoto]

Sorry I only have the manual in German.
The lever is connected to the wire to B. It is controlled by a vacuum. Are there any air leaks?

[neromoto]

add

[Peter Bristow]

Firstly, thank you both for your responses and especially ‘neromoto’ for the attachments to his replies.

Secondly – and to my considerable embarrassment – I have to admit that I mis-described the problem in my original posting, due to writing from memory. I had thought it was just the temperature control slider that was the issue, but, having had the car out for a run to check what Theo suggested, it now appears that the problem goes beyond that.

So, while the slider is definitely stuck solid towards the ‘cold’ end of its range of movement (see attached photo), I can now report that the air distribution controls are not working either. While it is possible to depress any of the ‘A/E’ ‘RISC’ and ‘SBR’ buttons this makes no difference to the actual air distribution – air is coming out of the screen demister vents only. On the upside, depressing ‘Stop’ has the proper effect of shutting off all airflow, albeit that the slider control stays stuck when it should move to the extreme left of its range.

The German language information covering the Heating and Ventilation System provided by ‘neromoto’ sent me to the English language version of the Concise Workshop Manual (CWM) at pp. 59-63 and so I now have a much better grasp of how the whole system works. In particular, I understand that the temperature control slider does not act to control the amount of hot engine coolant passing through the heater core, but rather to control the mixing of ambient temperature air and warm air, heated by passing over/through the heater core. So it is more accurately described as an air blender control.

I actually spent some considerable time looking at this section of the CWM, working out how the different system modes set out in the table on p. 60 mapped onto the diagram on p. 59. It was also very helpful to have ‘neromoto’s coloured versions of the individual system statuses. I’ll come back to those later.

The fact that I can only get air via the front windscreen demister vents regardless of which of the three air distribution option buttons is depressed indicates that Shutter C is stuck in position 2, where it blocks air from exiting via the cabin vents, forcing it up onto the windscreen instead. According to the CWM, that is the correct position for Shutter C when button ‘SBR’ is depressed. Shutter A should then be open in position 1, admitting outside air, while Shutter B should be in position 1, forcing all of that air to pass over/through the heater core before being direct onto the front windscreen by Shutter C in position 2.  All of these shutter positions should be controlled by the vacuum system. However, the air I am getting out of the windscreen vents appears not to be heated, but rather seems to be at ambient temperature. That is currently relatively warm, due to it being summer. This implies that Shutter B is actually in position 2 (or a position very near that), allowing the air admitted via Shutter A to bypass the heater core on its way to the demister vents.

Selecting ‘RISC’ should produce a different set-up. According to the CWM, Shutter A moves to position 1 so as to admit outside air, while shutter Shutter C also moves to its position 1, blocking the path to the demister vents and forcing the airflow towards the cabin vents. Both these actions are controlled by the vacuum system, but vacuum control of Shutter B ceases in favour of manual control via the temperature control slider, which is is connected to Shutter B by a sheathed cable. This allows Shutter B to be set in a variable position between its (vacuum controlled) positions 1 and 2. This is the air blender function in action, since this manual control allows the operator to control how much air passes over/through the heater core and how much is allowed to bypass it. The resulting blended air then passes into the cabin as directed by Shutter C.

However, ‘neromoto’ has added some handwritten annotations in his native German language to his coloured diagrams of the heating and ventilation system and I think these are saying that the system as shown in the diagrams is only valid for early cars, up to chassis no. 2785 (‘bis 2785 Chassis’). More specifically, on the diagram for the system in ‘SBR’ mode, I think he is saying that on subsequent cars there was a modification allowing manual control of the temperature of the air sent to the windscreen demisting vents. Here I refer particularly to his annotation ‘Altes System warm, neues System regulierbar’, which Google Translate renders into English as ‘Old system warm, new system adjustable’. This makes the modified system’s ‘SBR’ mode identical to ‘RSC’ mode in operation, save for the final direction of the air (to the windscreen rather than into the cabin). My Gamma berlina was built in 1978 with the chassis no. 5798, so, if I have interpreted the handwritten German annotations correctly, it would benefit from this modification.

In turn, this would explain why the air exiting the windscreen demister vents of my car (with the air distribution vacuum system seemingly stuck in ‘SBR’ mode) is not warmed air, as the CWM indicates it should be, but rather seems to be at summer-warm ambient temperature. With the temperature control slider ‘in play’ per the modification referenced above but seized in place towards the ‘cold’ end of its range of movement, the fresh air admitted via Shutter A is largely, (if not quite entirely), bypassing the heater core and therefore emerging from the windscreen vents still at ambient temperature, (or something very close to it).

Of course, all this speculation on my part doesn’t really get me any closer to a diagnosis of what has actually gone wrong. On the face of it, a seized temperature control slider cable shouldn’t affect the operation of the vacuum system other than the operation of that system on Shutter B, so why doesn’t depressing button ‘RISC’ sent air to the cabin vents (by causing Shutter C to move to its position 1)? To my mind this points towards issues with both the cable and the vacuum system.

On reflection, I think I shall be handing this problem over to my lucky mechanic! The car is already booked into the workshop for 17 July, for other matters needing attention. Meanwhile, I should be grateful;

1)   if ‘neromoto’ would please let me know whether or not I have understood his annotations correctly – and does the chassis number referenced refer to Gamma berlina models, not coupés?
2)   for any further suggestions as to what has gone wrong, now that I have given the correct full description of the fault; and
3)   for any information as to the physical location of the likely faulty parts and how to access them Presumably the dashboard cowl will need to come off?

I’ll feed this information to my mechanic, who I am sure will be very appreciative of it.

Thank you, PB.

[neromoto]

Hi Peter, how are you?
I use translation software, so I apologise if my English is inappropriate.
Unfortunately there is no Japanese manual, so I am using English, German and Italian documents.
Now, I checked my car just to be sure.
My Berliner had not been run for several weeks. First of all, I moved the temperature control lever before starting the engine, and it moves smoothly from side to side.
The vacuum tank is not under negative vacuum pressure because the engine has not been running for a long period of time.
Starting the engine I check the temperature control lever again and it does not move (STOP positionn).
'The lever moves smoothly when I put it in the RISC position.
Assuming that the cable is not the cause.
1. pull out the hose from the vacuum tank, release the negative pressure and check if the lever moves.
2. if the lever does not move, the actuator, check valve or hose may be blocked. Alternatively, the switching device in the controller may be broken.
3. remove the control unit, unplug the vacuum connector (No. 54) on the back side and check if the lever moves. If it moves, the actuator is normal. The controller may not be switched. If the lever does not move, the actuator or valve may be faulty.
4. It is unlikely that the cable itself is sticking. To check the cable, you have to disconnect the actuator side of the cable, which is a hassle.

I am not sure if my idea is correct. Can anyone give me some advice on this?

[Theo]

Firstly, thank you both for your responses and especially ‘neromoto’ for the attachments to his replies.

......

Hello Peter,

Since the buttons other than the stop button don't work and the lever is locked in cold (as it should be once the stop button is pressed) I suspect you have a vacuum problem.

Press all buttons several times WITH THE ENGINE OFF so it's not producing vacuum or disconnect the vacuum pipe from the accumulator. Once you've emptied any accumulated vacuum, try moving the temperature lever. If it moves then your problkem is certainly with the vacuum system and not a mechanical one. Assuming it is a vacuum problem, first think to check is the multi-pipe connector on the back of the control unit. This has a metal clip holding it in place on my car which is not shown in the photo below. If the multi-pipe connector is tightly in place, you must have a vacuum leak from one of the pipes, a split diaphragn in one of the control valves or a faulty heater control unit.

[neromoto]

Parts list

[Peter Bristow]

Thank you both for your further postings to this thread and especially to 'neromoto' for all the images he kindly provided. And my apologies to him for not appreciating that he is our Japanese correspondent!

I tried Theo's suggestion of multiple depressions of the air distribution control buttons so as to fully dissipate any residual stored vacuum, but to no avail. The temperature control slider remained firmly stuck in place at a position towards the 'cold' end of its travel (albeit not at the extreme left position depressing the 'STOP' button would ordinarily send it to).

I will be passing this over to my mechanic to look at, but I'm sure he will find all the input on this thread very helpful, so thank you both again.