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MG Midget and Sprite Technical - Heater Fan Switch.

Car: midget 1500 / 1979
My heater fan is not working. I removed the fan motor and bench tested it and it works fine.
I removed the pull type switch from the dashboard and tested the switch and found it to be open circuit in both positions.
My question is this..
Has anybody had any success in physically repairing one of these switches?
Thanks.
G M Bailyes

GM, Have you tried twisting the switch?

On my 1967 Sprite pulling the knob should open the air inlet vent (which is missing on mine!) via a bowden cable. Turning the knob switches the fan on and off.

Colin
C Mee

Yes, I have but for a mk1 Sprite. However, looking at parts diagrams, all the heater switches look similar. In my case one of the terminals had completely detached from inside the switch due to crumbling plastic/ bakelite and the flying lead pulling on it. It was a fiddly repair but I managed it, after several attempts, using JB Weld.

Assuming your contacts are still intact, it's probably the case that a terminal contact is not touching the switch "slider" (the metal rotating part). It might be possible to poke a thin screwdriver or dental type pick into the switch to maneuver it and tighten up the contact surface. If it's not working, you've nothing to lose. I didn't dismantle mine but that may be a further option. I wanted to preserve my original switches, whilst renovating the car, and every one of them needed attention but they do dismantle and are generally repairable.

Just seen Colin's post - you can only operate the rotary heater switch with the knob pushed fully in.
Bill Bretherton

Having just fitting mine I can also confirm that you have to turn the knob to the right whilst pushed fully in to start the fan.

It will not turn on whilst pulled out.

Before I fitted mine I sprayed electrical contact cleaning fluid all around and turned the switch on and off several times.

Need a good earthing point.

Guess I was lucky as also successfully bench tested mine but it also worked once I'd fitted and connected it all up.

Sorry I know I haven't really answered your question, but good luck.

https://www.mgmidgetrestoration.com/2022/08/heater-matrix-and-fan-rebuild.html


James Paul

GM,
Hi,

I had to repair my switch too, thankfully only an exterior problem. One of the two terminal posts was broken off so I had to solder the wiring onto the remaining bit of post.

My switch works both in and out, just a slight twist clockwise for on, and at all points in between.

I think my vent flap is 90º out because it closes when I pull the switch out.

If it is the internals of the switch that need fixed that may be possible but I think dismantling without breaking the bakelite end, where the terminals/posts are, and then recrimping the body onto that bakelite would be the critical points. That's just my guess, thankfully I didn't have to. And I don't think they are available any more.

One of my previous owners had replaced the horn push with a button on the dashboard, right next to the existing heater/fan switch, not practical but passed the MOT. Maybe you could do similar with a separate fan switch. Not concourse but at the least the fan will work.

Cheers
Nigel
N Broomfield

It's as Colin has put and yes Nigel your cable/flap/pull knob is the wrong/other way round, a quick squint at the Driver's Handbook will put you right.

Also the fresh air flap (valve) unlike how some think, doesn't really control heating temperature as that's the job of the heater tap on the cylinder head, again the Driver's Handbook gives instruction.

The fresh air flap (valve) regulates the fresh air (and fumes) going passed the heater matrix I always found keeping it fully open through winter and summer gave the most heat and fresh air, only closing it to prevent exhaust fumes (which is a waste of time with the hood dropped). I always kept the fresh air flap (valve) fully open through 18 winters and that way I got the most heat from the matrix (when I'd turned the heater tap on).
Nigel Atkins

Are you sure Nigel A?
The fan (should) only works when the knob is fully pushed in, and the flap must be open to allow the air to flow through the fan unit. So 'out' is Closed and Off; 'In and twisted' is Open and On. So Nigel B's flap valve operation sounds correct except the fan should only work in the one position.
David Smith

David,
thank you very much I totally misread Colin's post, thank you for putting things right.

Apologies to G M Bailyes.



I might be wrong (the Archives hold all) but I thought we'd sorted this out with Colin previously, he and another have/had the flap cable ar*e-about-face because they hadn't consulted the Driver's Handbook on its operation.

I think I suggested that the thought process behind having the knob fully pulled out into the cabin most all of the time was to provide somewhere to hang a handbag from but was corrected to it was as take-away bag hanger.

Nigel Atkins

Mine works as David Smith describes. I cant see how it could work in any other way.
Chris Madge

Chris,
if you connect the single wire inner cable to the fresh air flap (valve) with it 90 degrees out you've reverse the knob in-out positioning. If the electric side of the combined switch is working then it will turn the fan motor on with the fresh air flap in the closed position.

The heater box won't explode with the fresh air flap closed and motor fan running as the heater box has openings. Many will know this as for a long time the combined switch/cable wasn't available so an entirely separate switch fan motor switch would be fitted so you could have the fan running with the fresh air flap open or closed or anywhere between.

Nigel Atkins

I think Colin got it right in his very first response! Mr Bailyes makes no mention of attempting to turn the knob and only refers to it's "two positions". It has three, in, out and turned about (when in).
GuyW

Just to clarify: My Sprite's flap valve is non-existent and the bowden cable almost seized. The valve was missing from the car when I bought it so I've never had cause to pull the knob in an out 'in anger' and I didn't realise that the switch doesn't work when pulled out.

I can, however, confirm that my switch works by rotating it when fully pushed in, it won't turn when pulled out even the slightest amount.

New replacements for the flap valve are either unavailable or extortionate and replacing it hasn't been a priority as I hardly ever use the fan except to clear the misty screen on a wet day - partly because, with no duct present, it's drawing air from the engine compartment. I'll get round to sorting it one day.

Colin
C Mee

Guy,
the bit David spotted and I misread was "pulling the knob should open the air inlet vent", pulling would have the fresh air flap closing.

Below, by coincidence, is from 'the good book' for a Austin Sprite Mk4 (HAN 10)(1970).



Nigel Atkins

Colin,
I'll have to have a word with the scrutineers as that sounds like you are cheating to me, you have taken the car from standard by reducing the weight of the car with hidden missing parts, weights will have to be added to the heater box.

I don't know how you sleep at nights, look out for the chap in the shed as he will walk across to you one day.

P.S. I don't know why but I always type your name as Coilin so if you could reregister you name as that with at least the track then it would speed things up when I inform them. Thank you.


Nigel Atkins

Nigel, I wasnt replying to your comment about the movement of the flap when pulling/ pushing the control knob. That is pretty logical and obvious. My comment was that maybe Mr Bailyes hadn't appreciated that the switch is operated by rotating the knob (when pushed in) and not by pulling it. Unlike the wiper control knob!

Although the "heater box won't explode", there would be little point in having the fan operating if the duct carrying air to it is shut off. And if you do have the duct in place there are times when you do want to close off the ram effected air supply perhaps to shut off fumes from other cars when in slow heavy traffic. Or maybe you want to moderate the amount of hot air coming in and its not convenient to stop to open the bonnet to close off the heater tap.
GuyW

Sorry Guy, but as you've 'pushed the button' logic can be a funny thing, logic to me is the knob is fully pressed in to the dash to have the fresh air flap fully open and not always be taking up cabin space, unless you want somewhere to hang your handbag or take-away bag.

Also you could say the combined knob/switch has four positions, in, out, left, right or five for the variable hokey-cokey.

IIRC the 1500 windscreen wiper is on a rocker switch.

I totally agree with there's no point having the blower motor running with the fresh air flap shut it was just that previously comments were made about dire consequences if you did and I felt it'd be more of a slow fuse effect than a quicker more violent action.

Good point about closing the flap reduces the effect of the heat getting in the cabin as some thought the opposite would happen. As I've put before having used Spridgets through a good few winters I always kept the fresh air flap fully open to get the best effect if I had the heater tap open.

GM's probably repaired it by now. 😆

Nigel Atkins

Also, Mr Bailyes's question was asking if anyone had been successful in repairing the "switch". The switch, to my mind, is the electrical part of the control which is why I described my experience with this. However, I realised after Colins comment that the OP may not understand how the control works. It would be useful to have some OP feedback.
Bill Bretherton

Nigel: "logic to me is the knob is fully pressed in to the dash to have the fresh air flap fully open". Exactly! 😁
GuyW

Well unless you were pulling my leg previously you said you had the knob fully pulled out for open - but I have fell for your tricks before with you taking advantage of my trusting nature - and my gullibility, that's taking advantage of the unfortunate, shame on you, how do you sleep.
Nigel Atkins

mine stopped working on my previous 1500 and i tried to fix it but it was past fixing so i fit a mgb fan switch in place of the panel lights switch which i connected the wires together, so panel lights are on when lights on.
mark heyworth

Nigel Atkins, you're off my Christmas card list (even though you weren't actually on it in the first place 'cos I don't have an address!).

You really did talk to the Scrutes didn't you?

For the first time in 10 years of hill climbing, the scrutineer told me off for having an open heater intake in the engine compartment! He admitted to having been a Spridget racer in the past so knows what to look for in them. He was happy when he saw it again gaffer taped over and recommended flexible aluminium ventilation duct for the main hose and the blower/ heater matrix link.

Apart from that I had a great weekend at Harewood and finally cracked the 80 second barrier. There were three Spridgets in my class, two 1398s with twin-choke Webers and soft 1B tyres and one 1310 with twin SUs on ordinary 1A tyres so it won't be a surprise to you that I came last in my class - but I wasn't quite the slowest car of the day overall!



C Mee

Colin,
you'll never doubt my influence again!

You know you should of course always follow the book (is it still blue) and I think I did mention I'd been to Harewood.

I'm sure it won't come as too much of a surprise at all that I don't celebrate or enjoy Xmas so you'll have to think of something else.

You should be thanking the scrutineer and I for finking about yer 'elf & safety.

And - without being poisoned you clocked your best so if you get any winnings in the future I will expect a proportion.

You never know who reads what on a public forum, especially if they've been tipped the wink.

Who knows if you'd used your Spridget on the roads a bit more maybe you'd have not got a former Spridget racer inspect your car. 😉
Nigel Atkins

Thanks all for your very useful and informative comments. To start with, I confess, it's true that I misunderstood how the system operated, I didn't realise that twisting the knob whilst in the 'in' position operated the fan. I did remove the switch assembly to find out how the mechanics of the system worked and to check the condition of the electrical contacts. Also, I removed the fan motor and gave it a good clean and repainted the housing before refitting.
So, being a newby Midget owner, the exercise now means I understand how this system works if I get any future problems I'll be in a better place to sort it out.
Thanks again, this is a great forum to find out from the more experienced owners. I've no doubt I'll be back asking more questions. Bye for now. :-)
G M Bailyes

This thread was discussed between 14/09/2022 and 22/09/2022

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