Talk Morgan Forums Morgan Sports Cars Maintenance & Servicing Fan Speed Knob

Wow, what a super neat solution that would be

Great idea Rog, I'll investigate

Much more analogue solution, but I fitted one of these https://www.carbuilder.com/uk/fan-speed-conversion-switch-three-position

I already had a three speed fan on the aftermarket heater, but the fan was so powerful that even on the lowest setting it was cooling the heater matrix. I fitted it into the lowest fan setting, and now get a consistent warmth from the heater. It does mean I have a 5 speed fan setting!

Just took the switch of the car and after some continuity testing can confirm.

Fitted to my GDI is a 3 position 4 pole switch.

I tried connecting Poles A & B together and confirmed that positions 1-6 then had a single pole.

I didn't understand the discussion around combining poles to provide more Amps, and I don't know at this stage how many Amps I need, I will need better (Waterproof) Fans and probably will go for 2, I just had 1 for testing, so will continue along the Relay route to be safe.

So next thing to do is get a wire through to the fuse box and re-solder the leads to the right positions, then the Switch and Dash can go back together.

Mark see below, specifically the 4 pole 3 way variant you have proven you have.



If you were to connect poles A, B, C, D together. Then connect positions 1, 4, 7, 10, then 2, 5, 8, 11 and so on for position 3, you would end up with a single pole 3 way switch. Because the current was split four ways though the switch would handle 4 amps.

You require 4 positions though so the 2 pole 6 way switch variant with the mechanical stop set at position 3 would be a good choice. You could still double up the two poles and four positions as above to achieve 2 amp current handling.

Hope this makes sense.

This was demonstrated to me by the mechanic at Borghi's after I had burnt out the circuit board and was part of the incentive to change my dash. When the fan is running at high speed and you turn the engine off you see the various dash warning lights fade slowly because the spinning fan motor becomes a generator and feeds power back into the system.

It almost makes one wonder if the heater fan system goes back to when cars had a positive earth system

Part of Borghi's dash fix was to reverse the wiring to the fan to the more conventional system so that power goes to the fan from the switch/relay rather than the fan constantly having power and being earthed via the switch/relay. I don't know the technical details of how this was done.

Hi,

Any ideas why positions 2 & 8 have been connected?

2 is Fan position 1 (low), nothing connected to 8.



I want to move 2 to 3 so should I also move this connection?

No idea Mark. All the connections I've seen just use the A pole ground (black), position 2 fan slow (blue) and position 3 fan fast (yellow or slate).

Ditto - Is that a secondhand switch I see, that might have been used before?

PS – Mark, be super cautious modifying your car…

The fan motor itself cannot have a permanent live connection Peter since there are two speeds each requiring a switched positive feed. It's only the relays that have permanent live feeds to their coils allowing ground/return triggers, one each for fast and slow fan selection.

Ground triggered relays tend to be the norm now.

I wonder if that was the reason they poked these two diodes (on later cars) into the high/low motor feeds, in an ‘attempt’ to suppress some of the motor’s back EMF and protect the PCB?