heater fan switch

[malc4d]

I have seen that the switch was also used for a headlight switch on some cars. Anyone know if there is a difference in this switch when used in the A/C setup ?

[trunt]

I have seen that the switch was also used for a headlight switch on some cars. Anyone know if there is a difference in this switch when used in the A/C setup ?

Thats what I just came to search for! The A/C switch MUST be different as the Fuse would blow (pin 1 is shorted to pin7 on the standard one which is also used on the MG/TR) and the whole circuit would not work. The problem is finding a part number as it is not shown in the parts list. I remember some reference to a microfiche. I'll keep looking. If not I am sure I can do it with a relay and a diode!!

[malc4d]

I would contact

Michael M. Coffey
401 Brighton Drive
Clarks Green, PA 18411
Phone: (570) 586-1810

In fact ..go visit. he will be able to help loads.

[trunt]

OK on Michael .... on Both Forums...

But to answer your question there are some posts that seem to indicate that they are different,e.g. search for one that says "Hold the egg nog!"

Referring the the drawing below. The red lines indicate +12v, the black lines Ground. There is an inset of the MG/TR/ non ac Stag switch showing the connections at the three positions. Note that pin 6 has +12v and it is shorted to pin 7 ground in the off position (and low position. This blows the fuse, also if you turned the a/c on that would also blow the fuse (if it was not already blown)

For this to work,
initially both motors are supplied with 12v at each end and are wired in series, they are not running.

In the off position pin 1 should be shorted to pin4 (blue) this allows the a/c switch to run the fans at low speed by energizing relay 104 which grounds the end of the motor 106 and they run at 1/2 speed as they are in series.

In the low position pin 6 should be shorted to pin 4 (green) the +12v on pin 4 does the same, energises relay 104 and they run at 1/2 speed.

In the high position pin 6 and 4 are open again relay 104 now supplies 12v to motor 106 and pin 7 is connecting ground to pin 8 (black) this grounds the other end of both motors and they run at high speed.



So the switch I would love to find has this wiring

Off pin 1-4
low pin 4-6
Hi pin 7-8


*EDIT* since finding this switch I realise that it has a pin 2 INSTEAD of pin4 see below--

[trunt]

So here is my idea to make it work with an MG/TR/Stag non a/c switch




Wires to pins 4 and 6 are swapped pin 4 now has power and pin 6 feeds the speed change relay now the a/c being switched on will actuate the relay and give low speed.
A diode is added on pin1 to stop the power on pin4 from feeding back to power up the A/c system
The ground on pin 7 is removed and connected to a new relay.
Pin 8 now powers the new relay which grounds the center point of the two motors and gives High speed.

Since posting this I realise that a relay could be used instead of a diode, simpler!

[malc4d]

Cant you get the proper switch from Mike ?

[trunt]

He is not answering me..

Plus nowhere have I seen a part number for the A/C switch, just the common one..

Anyways, This was a good mind exercise.. and maybe a relay and diode is cheaper-- I have the common switch from my Mk1 ...plus a diode and a 12v relay for that matter!

[trunt]

I did find this eventually,

The AC blower switch is Lucas 39257A, Stanpart 151243.

http://www.triumphstag.net/start/technical/partslist/diagrams.php?diag=03-17

[trunt]

OK so a year on I finally got hold of this elusive heater blower switch for A/C cars. It seems that an easy way to spot it is it having a pin-2 rather than a pin-4. It does indeed work differently to the standard switch from Heater cars (and TR4, MGB etc.etc.)


OFF =1-2 shorted
LOW =2-6 shorted
HIGH =7-8 shorted

here's a picture:-

[mole42]

Excellent work Sherlock!

Not that I need an A/C switch in England (a dehumidifier would be more appropriate) but now that the correct part number is on the forum it’s a searchable item.