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Can anyone tell me what the supply requirement is for what I think is standard rear heated window? I am guessing around 10 amps given the in line fuse rating but would prefer to only have to wire it once :rolleyes:

I am assuming the relay is a standard one and that I can use one of the spare Carling switches on my Mud console.

Also there seems to be a voltage sensitive switch and a diode wired into the circuit from looking at the diagram - are these LR main dealer supply items or am I likely to be able to source elsewhere (if so what sort of values am I looking for)?

Finally, there are two terminal on the heater element, neither marked. Is there any convention as to which you connect to +ve and which to -ve?

Once I know about the diode and voltage sensitive switch I will start ordering up the coloured wires!

Thanks for any help.

Malcy

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Can anyone tell me what the supply requirement is for what I think is standard rear heated window? I am guessing around 10 amps given the in line fuse rating but would prefer to only have to wire it once :rolleyes:

I am assuming the relay is a standard one and that I can use one of the spare Carling switches on my Mud console.

Also there seems to be a voltage sensitive switch and a diode wired into the circuit from looking at the diagram - are these LR main dealer supply items or am I likely to be able to source elsewhere (if so what sort of values am I looking for)?

Finally, there are two terminal on the heater element, neither marked. Is there any convention as to which you connect to +ve and which to -ve?

Once I know about the diode and voltage sensitive switch I will start ordering up the coloured wires!

Thanks for any help.

Malcy

If the fuse is 10A, then 10A it is (use 18A cable to keep the voltage up at the far end). The factory arrangment means that the heated rear window won't come on unless there is a decent battery voltage (e.g. the voltage sensitive switch says so). These items are also called Voltage Sensitive Relays (VSR). The diode is to stop the HRW relay being back-fed by anything you might connect to the spare pick-up (little crescent shape top middle) such as a split charge relay.

All the above is available as seperate LR bits but don't bother as you'll pay a premium. You could also skip the VSR, but then there is a chance of leaving the window on with the engine off (it's fed by the ignition (white) line) - I'd fit it.

The white / black wire might already be present in the chassis harness, but possibly not.

It doesn't matter which way round you connect the heater element, whatever suits you door, but you should run an 18A black wire between the door frame and the earth stud at the back of the rear tub, as the hinges aren't brilliant conductors.

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  • 3 years later...

Rather than replace my rear window with one that has a heating element, I was considering fitting a Maplin Auxillary heater (A75FL) to the rear door. It pulls 150W and has a 15A fuse. Presumably I'd have to run a complete new set of wires out to it due to the high current draw and swap out the fuse in the fusebox?

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Rather than replace my rear window with one that has a heating element, I was considering fitting a Maplin Auxillary heater (A75FL) to the rear door. It pulls 150W and has a 15A fuse. Presumably I'd have to run a complete new set of wires out to it due to the high current draw and swap out the fuse in the fusebox?

Sorry to hi-jack.

Have you actually used one of these that you're on about. I was thinking of one for the passenger door window. Would it get hot enough ?

As for my rear window. Well I can't see out of it. I have heated mirror glasses instead.

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If you're talking about the mini heaters with a fan and electric elements, like a squashed hair dryer, don't waste your money. Their fan output is pathetically asthmatic but the heating elements are so weak that even with the slow airflow, they have virtually no influence over temperature.

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I don't have this problem as I used the HRW switch to switch a Disco fan fitted at the front to push air through the aircon element. My Defender didn't come with an aircon fan as standard. As I had never ever used the HRW this wasn't a problem. :i-m_so_happy:

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If you're talking about the mini heaters with a fan and electric elements, like a squashed hair dryer, don't waste your money. Their fan output is pathetically asthmatic but the heating elements are so weak that even with the slow airflow, they have virtually no influence over temperature.

Yes that's what I'm hearing. Now if I could get an old fashioned electric fire element, just the wire, I'd make a window heater.

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  • 4 weeks later...

I bought the Maplin heater A75FL a year or so ago for use as a rear window demister in my Ibex 250 hardtop. Never got round to fitting it because of fear of a malfunction causing a fire at the rear of the vehicle. Recently, with two dogs in the back, putting the standard Defender heater on full blast it has taken about 45 minutes to clear rear window. I thought that the trouble is that the air is not ciculating much at the back so decided to fit the Maplin unit and use on cold fan only just in case it would help. Easy to fit level with the top of the window and aim diagonally down, and existing circuit for heated rear window can be used (heated rear window is not available for this Ibex and I did not want to use a stick-on type).

When window has misted up enough to block view, then to my surprise it has worked very well and clears window in about 5 minutes, but not yet had extremely heavy misting to test it on.

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  • 2 weeks later...

I'll give it a go then without the heating element. I've got a spare one and the connector for the rear window is working. It also helps that my rear door card is plywood that will need swapping out after the winter so I can screw it onto that. If it works, It hasn't cost me very much. I'll probably pull out the heater element if it stays there so there is no risk of the fuses blowing due to somebody fiddling with it.

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For your infos, I have measured 12 amps to the HRW in an old style door. Mine seems to rely on contact through the hinges for earth return, and I found a bit of improvement could be had by putting a wire between door frame and body. Rather than use a VSR, you could just feed the switch from an ignition only supply (as per standard), assuming the switch just works a relay (again as standard).

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Yes you could fit it on the door, but mine is on the main body aimed diagonally down. Because it blows and clears a fan-shaped area it is effective over the whole window. Also, being near the roof it is out of harms way and also does not suffer from vibration when door is slammed shut. I think it is a good idea to disconnect the heater circuit.

As you say, you might as well try it. Would be interested to hear how well it works for you.

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