Lotus Elan

Fan control questions

PostPost by: The Veg » Fri Sep 28, 2018 11:56 pm

It appears that my fan-motor is kaput despite working before I reassembled the heater and screwed it back I to the car...DAMN! Thank goodness the dashboard is still loose and the cooling system still dry. Will be pulling the heater back out to assess it, but in the meantime I'd like to be sure that all is well with the wiring.

I have a Lucas 4BR fan speed resistor, which of course is not shown in any of the three wiring diagrams I have, and is not mentioned in the WSM. Perhaps somebody with proper knowledge of the circuit can advise me here.

The resistor measures approximately 2.5 ohms. Is this correct? In either case, does the burnt spot on it's backside (see picture) seem suspicious?

There are two wires from the switch that connect to the resistor. One is green/yellow and delivers 12V only when the switch is in the bottom position. The other is red with what appears to be a brown stripe, and delivers 12V when the switch is is either the middle or bottom positions. This seems odd to me; does anybody think that like the sidelight switch, I may have mis-assembled the contacts in this one? My guess is that each 'on' position should only be delivering power to one wire.

And remember t this last detail the smoking gun that shows that the motor's demise is my own fault? :lol:
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PostPost by: The Veg » Sat Sep 29, 2018 12:24 am

Update: the motor turns out not to be totally kaput but I'm not convinced that it is healthy either. With power directly connected it didn't spin until I manually got it started, it didn't seem to love as much air as would be ideal, and if I manually stopped it (which was fairly painless), it stayed stopped. Will be seeking a new motor now just to be sure that I don't have to go back in after it again. I've seen some commonly available motors for MGA/MGB online. Anybody know if those would fit?

In the meantime, the questions in my previous post still stand.
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PostPost by: Bigbaldybloke » Sat Sep 29, 2018 10:37 pm

See attached picture, sorry no wire colours but easy to sort.
The top terminal on the resistor has a wire going to the motor plus the connection for high speed fan, the lower connection is through the resistor and hence gives low speed. Both wires supply 12v from the switch. The dangling white wire in the picture is actually the heater fan motor earth and needs a good connection to earth which should be via the body retaining bolt to the chassis at the front left of the heater.
Easy way to test is to disconnect both wires from the switch and apply a direct power supply to the top connection that is connected to the fan. The fan should run at the higher speed and should self start easily. If this works, disconnect the temporary power wire from the top connection and connect it to the lower one, if the resistor is ok the fan should run at the lower speed, again it should self start. I suspect you have a poor earth if you previously tested the motor and it was ok.
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PostPost by: wotsisname » Sun Sep 30, 2018 7:19 am

If the resistor is burnt out there is a modern alternative.. Spyder were selling them a year or so back. I used some heatsink paste when fitting the new one.
I took my motor apart, watch out for the springs that keep the brush plate floating in the correct position ( hope this makes sense). Also don't separate the case until you've cleaned the shaft up. You need the bronze bush to remain in the case and not stay on the shaft.

[edit to correct spellcheck on phone]
Last edited by wotsisname on Mon Oct 01, 2018 2:45 pm, edited 1 time in total.
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PostPost by: Bigbaldybloke » Sun Sep 30, 2018 8:58 am

Just checked my manual, the resistor is show as part of the heater fan symbol. The red brown is slow speed and the green yellow bypasses the resistor to give high speed. Wouldn?t surprise me if the red brown has power at both low and high speed, it can?t do any harm as having 12v at both ends of a resistor just means no current will be flowing through it. If it helps I could check mine this evening when I?m home.
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PostPost by: The Veg » Sun Sep 30, 2018 1:14 pm

Thanks guys. Earth doesn't seem to be an issue as all the dashboard stuff is presently earthed to a jumper cable going straight to the battery, and the test in which the motor wasn't self-starting was also direct to battery, in that case the jumper cables direct to the fan leads.

Triple-B, yes please, and thanks in advance.
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PostPost by: Bigbaldybloke » Sun Sep 30, 2018 5:43 pm

Just checked, the low speed wire has power on it for both low and high speed fan operation. I must say that the low speed gives a pretty feeble air flow but it?s good on high speed.
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PostPost by: The Veg » Mon Oct 01, 2018 1:05 am

Thanks. Of course I'll be away all week on another biz-trip so won't be able to do any more with it until next weekend.
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PostPost by: The Veg » Fri Oct 05, 2018 10:11 am

Triple-B, if it is still accessible, may I ask you what the resistance of your resistor is?

Or anybody who can acces one?
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PostPost by: Bigbaldybloke » Sat Oct 06, 2018 1:06 pm

Just checked, 2.5 ohm. Took a few attempts as I struggled to get a good connection to measure it with my Fluke meter, but after giving the terminals a clean it gave a consistent reading of 2.5 ohms with the wires all disconnected from it.
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PostPost by: The Veg » Sat Oct 06, 2018 3:27 pm

Thanks, much appreciated! I owe you a pint should we ever be in the same place.
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PostPost by: john.p.clegg » Sat Oct 06, 2018 3:59 pm

All you need now is the current flow to work out what wattage you require...

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PostPost by: bob_rich » Sun Oct 07, 2018 11:49 am

Hi

When I refitted my heater on my +2 I found that if i did not get the assembly back just right the fan would not run very well. The resistor on my heater for slow speed is 1.5 ohms and the switching seem to work by selecting either the resistor (slow) or the motor (fast) to ground.

I rewired my car and I made up my own diagram and have copied the heater motor circuit out for you if they help and attached it below. Ignore the Connector C6 and FS7 reference as I modified the fusing and connectors that linked to the dash. The circuit is as it was on my car

Hope this helps Best of luck

Bob
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PostPost by: pharriso » Sun Oct 07, 2018 12:21 pm

Mr. Veg, this is the wiring from the Plus2S wiring diagram:

plus2heater_wiring.jpg and

All as expected.

It sounds as if your motor brushes are worn out. The Motor should be easy to strip down & the brushes easy to replace?

I have several spare motors for the heater in the 2 seater, but they may be different to the Plus 2. Maybe you could post pictures?
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PostPost by: The Veg » Sun Oct 07, 2018 9:36 pm

This is the motor. It had a Smith's label on it originally but that has got lost. GGLC's cross-references list two different Smith's part number mbers for it, so I assume that they are interchangeable. I was unable to find anything on teh interwebz using either number. Ken at Dave Bean tells me that the Cortina MkII used the same motor. I'm also going to take some measurements and see if I can't find a more readily-available motor that would fit.
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