Heated rear screen not working

keithyboy · 08-12-12, 03:08 PM

My HRW hasn't worked since I bought the car and now that winter's here, it's becoming a PITA. I did a bit of digging today and found:

1. It's not the fuse.
2. I'm getting zero voltage at the element (tried a separate earth too).
3. The switch lights up as it should.
4. I can't hear a relay clicking when the switch is pressed.

I'm thinking of trying another relay but I can't fund the bloody thing. None of the labels under the dash or the bonnet mention the HRW.

Help!

Tonks4x4 · 08-12-12, 03:16 PM

Take a look inside the rubber concertina between the boot lid and your car.

The wire will have gone brittle and cracked.

msh · 08-12-12, 04:37 PM

Relay for rear screen heater?

What's the car we're talking about?

keithyboy · 08-12-12, 04:50 PM

Quote:

Originally Posted by msh

Relay for rear screen heater?

What's the car we're talking about?

Sorry, it's a '93 C4 100 Avant.

msh · 09-12-12, 01:13 PM

So, did you tried as Tonks mentioned?

As for relay - I presume C4 A100 should have nothing that could be called relay in rear screen heater circuit and that it was only C4 A6 with which was introduced heater switch with built in relay and auto off function. You can check that for your car simply - just remove front of heater switch and take a look - if there's just two bulbs, it's a simple switch, if there's SMD LED's - then it's switch with one or two relays and some electronic inside.

Sabre75 · 09-12-12, 01:34 PM

Quote:

Originally Posted by keithyboy

My HRW hasn't worked since I bought the car and now that winter's here, it's becoming a PITA.

I know the feeling; it's even worse when your main heater doesn't work either!

Quote:

Originally Posted by keithyboy

1. It's not the fuse.
2. I'm getting zero voltage at the element (tried a separate earth too).
3. The switch lights up as it should.
4. I can't hear a relay clicking when the switch is pressed.

Sounds like you've been throught the same checks I did. If the '93 C4 is anything like my '90 C3 then (as msh said) your HRW system doesn't have a relay; the circuit runs directly through the switch.
Does your switch have 2 small bulbs inside it? One to illuminate it when you turn the lights on and a second that lights-up an orange triangle when you press it? If so it sounds like the C3 switch. It works by having brass contacts that deflect when you press the switch. In the on positions the tabs rest against the contacts to complete the circuit, and in the off position they are deflected up to break it.
If you remove the switch and open it up you can check whether (a) the tabs make contact in the on position, and (b) the tabs and contacts are 'tarnished' and so make a bad/no connection.
In my car it was a combination of the 2; I got a piece of emery paper in to clean the contacts (very fiddley) and then managed to re-bend them so they contacted properly (also fiddley!). At any rate it's probably worth pulling the switch and testing the continuity in both positions.
I hope this helps and good luck

keithyboy · 09-12-12, 04:34 PM

The lack of a relay explains why I cant find one then! If the switcg is lighting up it shouldn't be too hard to trouble shoot. I'll start with the switch and work from there. Cheers.

Tonks4x4 · 09-12-12, 04:42 PM

Why don't you save some time and start at the back like I suggested?

keithyboy · 09-12-12, 05:00 PM

Quote:

Originally Posted by Tonks4x4

Why don't you save some time and start at the back like I suggested?

Sorry, should have said, I can't find any breaks in the wire.

Tonks4x4 · 09-12-12, 06:00 PM

The wire you are looking for from the back of the switch down the length of the car should be white/yellow

08-12-12, 03:16 PM	#2
Tonks4x4 4 ring whore! Classic Audi Club Member Join Date: Oct 2008 Location: Huthwaite, Nottinghamshire Posts: 2,607	Take a look inside the rubber concertina between the boot lid and your car. The wire will have gone brittle and cracked. __________________ http://www.tonks4x4.com

09-12-12, 04:42 PM	#8
Tonks4x4 4 ring whore! Classic Audi Club Member Join Date: Oct 2008 Location: Huthwaite, Nottinghamshire Posts: 2,607	Why don't you save some time and start at the back like I suggested? __________________ http://www.tonks4x4.com

09-12-12, 06:00 PM	#10
Tonks4x4 4 ring whore! Classic Audi Club Member Join Date: Oct 2008 Location: Huthwaite, Nottinghamshire Posts: 2,607	The wire you are looking for from the back of the switch down the length of the car should be white/yellow __________________ http://www.tonks4x4.com

08-12-12, 04:37 PM	#3
msh 4 ring whore! Join Date: Jun 2008 Location: Rucava, Latvija Posts: 3,816	Relay for rear screen heater? What's the car we're talking about?

09-12-12, 01:13 PM	#5
msh 4 ring whore! Join Date: Jun 2008 Location: Rucava, Latvija Posts: 3,816	So, did you tried as Tonks mentioned? As for relay - I presume C4 A100 should have nothing that could be called relay in rear screen heater circuit and that it was only C4 A6 with which was introduced heater switch with built in relay and auto off function. You can check that for your car simply - just remove front of heater switch and take a look - if there's just two bulbs, it's a simple switch, if there's SMD LED's - then it's switch with one or two relays and some electronic inside.

09-12-12, 04:34 PM	#7
keithyboy Grown up member Join Date: Jul 2012 Posts: 66	The lack of a relay explains why I cant find one then! If the switcg is lighting up it shouldn't be too hard to trouble shoot. I'll start with the switch and work from there. Cheers.