SP250 Heater Blower Switch

[Patrick]

The electric blower switch mounted on the hot/cold selector has disintegrated and is not repairable. The switch is mounted on the selector arm by 2 screws. I realize that I can mount an after market flip switch to the dash to perform in its place. However, I am wondering if the original switch is available. The hot/cold selector works perfectly. Also I know the entire control with switch can be obtained from Manners.
Any help would be appreciated.
Patrick

[Vortex O'Plinth]

Laurence Jones used to be able to get these rebuilt - he may still be able to do so. Contact him on the SP250 Owners Club site. Even if rebuilt it would be a wise precaution to fit a relay in the circuit; the switch passes quite a high current through flimsy contacts and arcing will probably cause failure again in time.

I preferred to replace the switch with a modern microswitch and relay with some simple modifications - see here. If this post is of interest and you are unable to see the pictures, let me know and I'll email them to you.

Another option is to use a big Healey switch - see here - although this reverses the hot and cold slider positions.

[rogerharrop]

Please email me the micro switch replacement photos roger@rogerharrop.com

Many thanks

Roger

[Vortex O'Plinth]

Please email me the micro switch replacement photos roger@rogerharrop.com

Many thanks

Roger

Link to the piccies sent.

Regards

Nick

[rogerharrop]

Great thanks Nick

[Patrick]

Nick, I think the micro switch with relay route is the way to go. Please email photos and any relay wiring diagrams to gretch1209@yahoo.com.
Thanks.
Patrick

[Vortex O'Plinth]

Since there seems to be some interest in the posting on the old forum, I thought it might be easier to replicate it here - with the photos visible!

I suspect many SP owners will have more familiarity than they’d really like with this particular bit of not very reliable good old British engineering.



The Smiths heater fan switch is a simple but not a very robust piece of design, and having spent some hours fiddling around with mine to little functional effect, I decided to see if I could devise a more reliable replacement. The core problem is the points assembly and its plastic mounting block, so from a bit of old Tufnol I fabricated a new block to mount a modern microswitch . The block retains the dimensional envelope of the original and still provides guidance and detent for the operating lever, but carries the microswitch on two aluminium mounting arms. In fact, the only part discarded is the original switch block.

These are the new and old side by side.





Maplin provided the microswitch and I shortened the actuating arm to retain operation by the original cam on the operating lever.



Switch is shown in the ‘ON’ position. After a lot of push-pull on the switch knob it’s till working fine so hopefully will continue to do so reliably back in the car.

I’m not sure of the current draw of the fan motor, so it will be prudent to wire it in via a relay, but otherwise to all external appearances it will look standard.



I didn't include the wiring diagram for the relay as it's pretty straightforward. This general diagram for a typical 4-post automotive relay (cost about £2) illustrates the wiring....

....for 'dash mounted light switch' read the new microswitch and for 'light' read fan motor. The relay can be mounted in any convenient position under the dash to maintain originality of appearance.

The switch has been in operation on my car for 7 years now and still operates consistently.

[JohnM]

Neat job as always, Nick - that's a great addition to the technical archive.
regards,
John

[Patrick]

Thanks Nick, exactly what I was looking for.
Patrick