90 heater head scratcher

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S

Should know better!!

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Chesterfield
Afternoon all, just wondering if anyone can give us a clue as to whats going on with my heater!
Its a 1985 90 recently purchased the previous owner had bodged the blower fan with a simple toggle switch bypassing the dash slider control (it worked well the fan wheezed its self around). The toggle switch had a jumper cable from one of the green wires (from the original switch) and another wire (earth maybe?) connected to it. Now after stripping the dash slider switch and cleaning all the gunge of the brass contacts I thought I maybe in with a chance of it working once I had connected all the original connectors back on- sadly no dice.
So my question is what else could be stopping the original switch working?
Electrics arent my strong point but I do have a rudimentary grasp.
Thanking you in advance, Sean
 
Sean, the electric slider is like a potentiometer :. increases/decreases resistance to the slider setting output therefore increasing/decreasing the voltage [and current] to the heater fan. This in turn supplies little -to- max' heated air into the cabin. They're very simple devices.

Do you have a DVM/volt meter to hand? If so, with ignition switched on measure voltage output across the slider switch - this should increase/decrease as resistance [ohms] increases/decreases. If you are getting permanent open circuit at 0volts the slider is open circuit [broken]. This normally happens at the start point of the winding, or if there's a ballast resistor across the circuit there's a good chance the resistor is faulty. Both faults can be repaired/a new resistor bought online.

Once done, it's time to check the wiring from your now working slider to the heater fan - with ignition on, measure the voltage at the heater fan terminals. When set to 'Hot' you should see 12v or near to 12v. If anything less or 0v the supply wire from slider to the heater needs replacing.

Of course, the other side to check are the earthing points - make sure you have good clean/zero resistance [a clean 0v] between slider -Ve to the earthing point. If unsure, install a new black earthing wire local to the slider.

PS have checked manual wiring diagram [Haynes Manual page 13.18, diag#2] the heater fan motor earth is your middle connector pin/terminal
 
v8250 said:
Sean, the electric slider is like a potentiometer :. increases/decreases resistance to the slider setting output therefore increasing/decreasing the voltage [and current] to the heater fan. This in turn supplies little -to- max' heated air into the cabin. They're very simple devices.

Do you have a DVM/volt meter to hand? If so, with ignition switched on measure voltage output across the slider switch - this should increase/decrease as resistance [ohms] increases/decreases. If you are getting permanent open circuit at 0volts the slider is open circuit [broken]. This normally happens at the start point of the winding, or if there's a ballast resistor across the circuit there's a good chance the resistor is faulty. Both faults can be repaired/a new resistor bought online.

Once done, it's time to check the wiring from your now working slider to the heater fan - with ignition on, measure the voltage at the heater fan terminals. When set to 'Hot' you should see 12v or near to 12v. If anything less or 0v the supply wire from slider to the heater needs replacing.

Of course, the other side to check are the earthing points - make sure you have good clean/zero resistance [a clean 0v] between slider -Ve to the earthing point. If unsure, install a new black earthing wire local to the slider.

PS have checked manual wiring diagram [Haynes Manual page 13.18, diag#2] the heater fan motor earth is your middle connector pin/terminal
Click to expand...
Great thank you
That sort of makes sense to my fuddled grey matter- where would the resister/ballast be?
 
If there is one, looking at the diag', it would be inside/or in parallel to the slider...but the diag' doesn't show any resistor, just start/end points of slider as a 3pole switch; which of course it is not. Ever helpful LR[!]
 
v8250 said:
If there is one, looking at the diag', it would be inside/or in parallel to the slider...but the diag' doesn't show any resistor, just start/end points of slider as a 3pole switch; which of course it is not. Ever helpful LR[!]
Click to expand...
I dont think there is one just a earth and the two green wires going to the slider. My wiring diagram doesnt appear to show anything else between the slider and fan motor. God I hate car electrics
 
Should be three wires to the switch. Solid green is 12v in, and you will have green/yellow and green/grey out to the motor. One is slow speed and powers the motor via a resistor (internal to the heater unit) and the other is for high speed and bypasses the resistor. The slider also closes a flap to shut off the air if you push it all the way up.

Use a multimeter to check the resistance across each of the switch terminals in every position: in positon 1, two of the terminals should be close to 0 ohms between them. In position 2 all terminals should be connected. This will rule out the switch itself.
 
v8250 said:
Sean, the electric slider is like a potentiometer :. increases/decreases resistance to the slider setting output therefore increasing/decreasing the voltage [and current] to the heater fan.
Click to expand...

No it isn't.

There is a feed into the switch then two switched outputs, either 1 or 2 - 1 goes via a resistor and 2 is direct. The OP's bodged switch probably just went to main motor feed.

The variable aspect of the defender heater slider controls the mechanical flap via a bowden cable - nothing electric about it.
 
stc4848n.jpg
MAY HELP JOHN RICHARDS SURPLUS IMAGES
DEFENDER 12J UP TO 1986.png
 
Last edited:
discomania said:
No it isn't.

There is a feed into the switch then two switched outputs, either 1 or 2 - 1 goes via a resistor and 2 is direct. The OP's bodged switch probably just went to main motor feed.

The variable aspect of the defender heater slider controls the mechanical flap via a bowden cable - nothing electric about it.
Click to expand...

I think he missed the 1985 and Land Rover parts of the original post,
 
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