Two speed heater-getting it to work!

[JeffP]

Further electrical issues with the restoration of my '69 Elan Plus2! First, thanks to everyone who replied re my courtesy light issue. I ditched my aftermarket lamps went back to the originals and fitted a new panel switch - all is well.

I cannot get my two speed heater fan to work - I know it should be simple, but its not.

What I have:

The heater switch is the common 3 position toggle switch. 5 terminals, 1,3 and 5 test as being live all the time, 2 is live in position 1, 4 is live in position 2. Current wiring is a feed to the fan motor from the cigar lighter (always live).
Terminal 1 has a feed from the fuse box that also feeds to the indicator flasher. Terminal 5 has a feed to the handbrake warning light. A red wire goes from 3 to the three terminal resistor on the heater box and a red/white goes to the other terminal and a ground wire from the heater motor goes to the other terminal on the resistor on the heater box.

This does not work and appears to be the result of mods over time.

Question 1. Is the an example of ground side switching?. If so , where and how does this work with this switch set-up?

I now have the heater out of the car and have tried, what I believe should be a more correct set-up with power going to terminal 1 from the fuse box, then when switch goes to position 1, power goes from terminal 2 to the motor, I was hoping that connecting terminal 4 to the terminal on the heater box would give me a change of speed.

However, nothing works unless I ground the heater box resistor directly and then I can only get one speed.

Question 2 is does the heater box need to be grounded separately?

Question 3 Does the resistor vary current from the motor to ground or how does it work? Should it have a good ground to the heater box. It is fixed via a simple self -tapper?

Any other remedial steps welcomed!

Many thanks for your help

[stugilmour]

Will try to help, but getting a bit lost without a wiring sketch. No matter, here is how it works in general terms….

Whether the heater box is grounded is immaterial. The resistor should be electrically isolated from the heater box. I vaguely recall having issues with this when removing and remounting the resistor, might have been a crumbled fibre washer or some such? For testing definitely don’t ground the heater box as you may cause an intermittent short to ground until you get the resistor correctly mounted and isolated.

If the mounting screws are somehow grounding the resistor to the heater box at both ends it can cause a direct connection thru the heater box rather than the resistor and the fan might only run on high speed. I can’t recall what the exact issue I was having, but I recall it taking a bit of fiddling to get right before putting the heater box back in the car.

From my notes the +12v fan motor lead is Slate coloured (conductor colour 42 on Federal diagram), the fan motor ground is white coloured (conductor colour 33 on the Federal diagram). Your setup may be different, and obviously reversal will change the direction of rotation for the motor. Should be able to straighten this out easily with the whole heater box on the bench.

The White fan motor ground changes to the more standard Black ground wire colour at a bullet connector, and ultimately is directly grounded at the main ground bobbin on the right side dash mounting chassis bolt.

The high speed +12v supply wire from the switch goes directly to the “downstream” resistor terminal, the same terminal where the Slate motor lead is connected. This electrically “bypasses” the resistor and puts the fan on high when the switch is in position 3.

The low speed +12v supply wire from the switch is connected to the other “upstream” resistor terminal. This electrically puts the resistor in series with the Slate coloured motor lead, putting the fan motor on low speed when the switch is in position 2.

Check your switch carefully to ensure only one output terminal you are using is live at one time, and both are off in position 1.

Note my car is a ‘69 Federal with flat dash switches, so the individual terminals and stuff are probably slightly different, assuming you have the rat tail style toggles.

My loom is aftermarket, so wire colours may be different. Anyway, for reference the high speed wire from the switch is Green/Slate and the low speed wire from the switch is Green/Yellow. These are the standard British wire colours, although Lotus didn’t necessarily use them. Looking at a few Plus 2 diagrams Red/Brown and Brown/White look popular, but sure this varies by model.

The dash switch is supplied with +12v Green, Hot in Run and Start, Fused from one of the fuse outputs (or daisy chained from another dash component). Heck, there only was one Green fuse in the car originally anyway, the second fuse being Purple, Hot at All Times, fused. I see some later Plus 2 models with multiple fuse boxes use different wire colours. At any rate, you probably want the heater fan to be off when the ignition key is either off or accessory position, so there you go, that would be Green supply by definition. At least, that is how I set it up; works great to listen to tunes while parked.

I would post my wiring sketch but it is probably a bit confusing because I used two relays to reduce the load on the dash switch, so don’t think it would be helpful.

HTH. Let us know how you get on.

Some other top tips….

While the dash is out, make sure there is clearance between the lower edge of the heater box to the electrical connectors on the lowest row of switches. 90 degree “Flag Connectors” make this easier, but they must be covered with the correct boots.

While you have the heater box on the bench, definitely put new foam on the control flaps. The Plus 2 heater relies on the flap seals to turn off the heat, and the original foam is usually turned to dust so you may not see anything now. There are lots of excellent threads with great pictures on this important item.

Many owners have also modified the top front of the heater box to provide additional depth for mounting a more modern radio or head unit, although this is probably less of an issue with shallow depth purely digital head units widely available now.

Many folks have also added a coolant shutoff valve to be able to seasonally turn off the heater core, so something to consider.

Access to the heater core nipples is very difficult with the engine and transmission in place (you may have already faced this issue?), so best you can get the hose clamps secure and positioned for later access/tightening.

Cheers from Cowtown on the first day of the Calgary Stampede, the Greatest Outdoor Show on Earth, or so we are reminded this time of year! As the Canadian home improvement legend Shell Busey always signed of with, “It’s just that easy!”

[v6b5n4m3]

It sounds like you've done a lot of troubleshooting already. For your two-speed heater fan, ensure the heater box and resistor are properly grounded as this can affect functionality. The resistor should control the current to the motor, so a good ground connection is essential. Check all connections and grounds thoroughly, as poor grounding often causes issues in such setups. If grounding the resistor directly results in one speed, there might be an issue with the switch or the wiring setup. It could be helpful to use a multimeter to trace where the current is or isn't flowing correctly. Hope this helps.

[Bud English]

It sounds like you've done a lot of troubleshooting already. For your two-speed heater fan, ensure the heater box and resistor are properly grounded as this can affect functionality. The resistor should control the current to the motor, so a good ground connection is essential. Check all connections and grounds thoroughly, as poor grounding often causes issues in such setups. If grounding the resistor directly results in one speed, there might be an issue with the switch or the wiring setup. It could be helpful to use a multimeter to trace where the current is or isn't flowing correctly. Hope this helps.

The resister is just a resister that, in the low switch position, is placed between the hot contact of the switch and the fan motor. It need not be grounded and, in fact the resister element itself is isolated from it's mounting bracket that is attached to the heater box. The only ground need is the fan motor's white ground wire.

Stu's description above is entirely correct.

[gus]

Been a while, and both early and late wiring diagrams appear to be incorrect in not showing the resistor.
It should be easy to get the fan to run on high in the high position. Fan motor grounded, power to switch power, common leaving switch on the appropriate terminal. We will call that 'H'
Low, power should come out of the appropriate terminal on the switch and go first to the resistor and then to the hot side of the motor. Call that switch terminal 'L'
It occurs to me that the simplest way to accomplish this as there are not extra terminals on the motor, is to have the wire 'out' of the resistor to return to the switch terminal 'H' Sounds a bit odd, but should work electrically.
I cannot recall if the fan has two wires[power ground] as it has been a while, but if not then it needs the box to be grounded for its ground,

wiring the wrong switch terminal as common also has the result of only having one speed