lower temperature activator - Rolls-Royce and Bentley Forums
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post #1 of 18 (permalink) Old 09-17-2019, 05:46 PM Thread Starter
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lower temperature activator

Does anyone know the purpose of the microswitch on the lower temperature flap actuator. It is on all the time except when pin 4 is activated. This is the position where the "hammer head" on the lever, that I've arrowed, pushes up against the microswitch. The microswitch is shown in the wiring diagrams but doesn't give much info to it's purpose. The workshop manual does not mention it.
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1974 Silver Shadow
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post #2 of 18 (permalink) Old 09-18-2019, 01:53 AM
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Hi,


The schematics can be very difficult to follow where variable rotary switches are shown as it is hard to understand the circuits they are making/breaking at each step position.



Can you just confirm which terminals the wires were connected to as that works as a normally open, or normally closed switch and the part drawing schematic you show, the position in circuit is as NO(normally open) so looks like it should only make contact to close a circuit in the other positions.


Traditionally UK car schematics are always drawn in the totally unenergised condition with every item on the car drawn as switched OFF.



As the stepper motors only turn continually in the one direction I would assume this allows supply to the stepper motor itself when main switch is turned to OFF to allow the stepper motor to continue running till it reaches the OFF position. Just a first thought at the moment.



Which is your year and the schematic you are looking at as the one I just looked at for a quick looksee does not even show this contact in circuit.


All the best


Steve
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post #3 of 18 (permalink) Old 09-18-2019, 11:56 AM Thread Starter
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Hi Steve


Thanks for your interest. I can see from other posts you have considerable expertise on these cars.


Apologies for not including this essential information on my first post - the car is a 1974 SY1, SRX18501


The wiring diagram is Sheet 9 of the wiring diagrams section of the SY1 workshop manual. It is entitled "LEFT-HAND DRIVE SALOON AND LONG WHEELBASE NON-DIVISION CARS FOR COUNTRIES OTHER THAN USA AND
CANADA FROM CAR SERIAL NUMBER 16214" The car was originally exported to Germany, then exported to California, hence the "countries other than the USA" in the wiring diagram title.


From the first photo, terminal A is common. In the off position the meter shows continuity through terminal C, with terminal B showing no continuity. When the switch in pressed in, i.e. on position, terminal B shows continuity with terminal C no continuity.


From pic 2 you can clearly see there are wires connected to terminal A and C, so there is continuity at all times except for when the stepper is in pin 4 position and the "hammer head" on the rotating lever is pushing against the micro switch.



On the bench the stepper works fine. When I energise each terminal (1 to 5) the stepper moves to it's respective position. I can only think the microswitch is sending a signal to some other component when the pin 4 position is on.



Regards


Geoff
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post #4 of 18 (permalink) Old 09-18-2019, 01:13 PM
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Geoff,


Thanks for the update. My experience is 'limited' to certain things so not considerable. It is late now here in UK but will study schematics.


I am still of the opinion the micro switch possible acts like the internal switch on a windshield wiper motor. That is when you put your main switch to 'off' the power to the stepper motor would be interupted so it needs a supply to allow it to continue to turn the stepper motor internal motor till it reaches the closed flap position. Just like when you turn off the wipers half way through a wipe cycle the windscreen wiper motor still needs power until they reach the park/stowed position.



When you then turn your main switch to any position that supplies power to the stepper motor accordingly to the position selected but an immediate switch back to OFF would give no supply to stepper motor so flap would stay in the position it was in.


It is virtually impossible to follow the schematics line diagram through the rotary switch and indeed through the stepper motor.


I would do a simple test and from hammer UP position turn your ignition ON then main switch to open the flap so stepper motor rotates to open flap. Then disconnect the wire from the C terminal of the microswitch. Then turn the main switch to OFF and see if stepper motor returns to hammer UP position. If not then just put the wire back on and see if that gives a supply to stepper motor to rotate it to hammer UP position.


That should prove if it is like a self park supply. If this does not show up to have any effect then it is back to the schematics and anyone else with ideas or experience. Jake hopefully will read the post as he has lots of experience too on the electrics.



I have worked on RR Shadows for many years but still finding relays and switches I never knew of. I actually had this exact microswitch on the LHS on a 1978RHD SS11 where someone had been behind the fuseboard to fit a CB radio in the glovebox. They had moved the wiring just enough under the dash/facia the wire to the microswitch got wrapped around the stepper motor arm and pulled off the microswitch Lucar connection. I never thought what its function was but it was obvious which terminal it had come off so I just put it back on.



If you can do the test it would help. However you do need to look at what is happening on both sides as it may also have some interaction with driver/passenger side whichever RHD/LHD



All the best


Steve



Steve

Last edited by Steve E; 09-18-2019 at 01:19 PM.
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post #5 of 18 (permalink) Old 09-18-2019, 01:48 PM Thread Starter
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Hi Steve


Many thanks for your ideas on this. I will run the test you have specified, which is a very plausible reason for the presence of the microswitch. Should the test fail I will see if there are any obvious changes in the car when the micro switch is connected/disconnected.


Geoff

1974 Silver Shadow

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post #6 of 18 (permalink) Old 09-18-2019, 01:53 PM
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Geoff,


One other idea is it is in the fan motor circuit so with the wire disconnected from the microswitch you can see if your fan motor still works.


Can you also just confirm the actual colours/tracer colour of the two wires as it is hard to tell from the pictures.


Regards


Steve
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post #7 of 18 (permalink) Old 09-18-2019, 03:00 PM Thread Starter
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Hi Steve

I've just fitted the actuator with the microswitch disconnected. It ran for 1 revolution and stopped working. I connected the microswitch but it is still not working. I will fault find tomorrow.

The two wires to the microswitch are colour coded the same - brown with a red stripe - plastic.

I'll let you know how I get on tomorrow.

Geoff
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post #8 of 18 (permalink) Old 09-18-2019, 04:10 PM
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Geoff.

Did you have a problem with the lower temp flap actuator, or was it just curiosity that made you post here?
As the actuator is now not working, have you tried connecting the brown/red together to see if the actuator starts working again?
If it does, connect the wires back onto the micro switch when the actuator is still running and before the hammer hits the switch.

The switch is there for a purpose but looking at the wiring diagrams, I have no idea why.

Jake.
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post #9 of 18 (permalink) Old 09-18-2019, 06:18 PM Thread Starter
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Hi Jake

I've been rebuilding the entire heater system on the car for a few months now, at a very leisurely pace (house move also got in the way). I blanked off all the apertures in the bulkhead so I could still use the car, albeit without aircon or heating.

I removed the heater box and heater control box to find most of the foam lining had disintegrated and all of the rubber bushes had perished - not surprising after 45 years.

I'm currently doing a trial run refitting the heater control box, which, as you will know, contains the lower temperature flap. I want to make sure it all works in situ before fitting the control box permanently, i.e. using sealant around the rubber gasket to make sure no engine gases enter the passenger compartment. I don't fancy digging it out again.

I intend to spend tomorrow morning fault finding so I will include your suggestion.

I will report back.

Geoff
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post #10 of 18 (permalink) Old 09-19-2019, 04:01 AM
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Geoff,


Studying the schematics I think the microswitch is part of the water tap relays and water tap actuator circuit so unless the stepper motor that controls the flap iteself opens and allows the microswitch to make a circuit you will not energise these circuits to allow the water tap to open. Brown/red 'in' white/red 'out' is a key typical indication of what is seen on wiring through switches the main heater switch being the actual switch in this case. Also the dotted line around the microswitch indicates it IS linked to another system that is dotted lined......however again it is a common way shown on RR schematics and then us left wondering which one it is supposed to be linked to.



In this case the microswitch really has no function to do with the main heater control switch over the flap stepper motor function.


One other thing is when you changed your foam you may need to make sure it was not too dense so the stepper motor struggles to continue its revolutions. As I said the stepper motors just continually turn in the same rotation so the flap adjustment is quite critical so the flap just bottoms out to seal but not excessive requirement otherwise it provides too much resistance for the stepper motor to overcome.


Worse thing is those water tap relays are on a circuit board under the blower motor and not easy at all to get to to just do a quick continuity check and not much easier to get behind the main switch either on the lower facia to pick up a continuity test to the white/red from the brown/red on the microswitch when the main heater switch is turned to a functional position.



So I feel maybe you don't have a fault and will be doing something that would be very useful for future knowledge in actually establishing but a lot of work to help understand the shortcomings of understanding the links in the schematics.


Maybe if I can get to mine easily I could just disconnect the brown/red wire from the microswitch and see if the water tap under the bonnet/hood does still function. Or if anyone currently has their footwell trim out and lower dash they could do the test.


Its probably not that easy to prove on your car with everything disconnected as it looks like circuits are fed through the stepper motor as well as the main switch..


Hope some of this helps a little.


Steve
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