Ford Scorpio Forum
        (https://www.fordscorpio.co.uk/cgi-bin/yabb/YaBB.pl)
      

        General >> Problems >> heated front screen 24v
        
(Message started by: python9 on Feb 17th, 2009, 6:42pm)
Title: heated front screen 24v
Post by python9 on Feb 17th, 2009, 6:42pm
i changed the fuse box on the battery side everything works except the heated windscreen is not working  what could be the the problem none of the fuses are blown
Title: Re: heated front screen 24v
Post by gozz on Feb 17th, 2009, 7:40pm
python9.
Could you have knocked a connector off the bottom of the screen in the maul  :)
                                           GOZZ,
Title: Re: heated front screen 24v
Post by gost on Feb 17th, 2009, 7:44pm
When mine didnt work it was a relay
Title: Re: heated front screen 24v
Post by Snoopy on Feb 18th, 2009, 6:54pm
The actual windscreen itself could have broken . The very thin wires embedded in the screen do break but not usually ALL of them . but the first thing to checlk is the earth connections situated at the bottom of the screen on BOTH sides as its divide into two parts.
Title: Re: heated front screen 24v
Post by python9 on Feb 18th, 2009, 7:13pm

on 02/17/09 at 19:40:40, gozz wrote:
python9.
Could you have knocked a connector off the bottom of the screen in the maul  :)
                                           GOZZ,

where are the connections gozz
Title: Re: heated front screen 24v
Post by gozz on Feb 18th, 2009, 8:12pm
Right in the corners of the screen,under the bonnet,just outside the edge of the plastic grille.
                GOZZ.
Title: Re: heated front screen 24v
Post by python9 on Feb 19th, 2009, 2:12pm
there connected okay gozz it must be the switch on the dash surround or the relay it was working okay before i changed the fusebox and there is no wires broken i checked my windscreen with a magnifier
Title: Re: heated front screen 24v
Post by python9 on Feb 19th, 2009, 9:20pm
tried another relay still not working
Title: Re: heated front screen 24v
Post by Cosray - The Hague - Holland on Feb 28th, 2009, 8:20am
The windscreen heater is rather special as it's driven and governed by the Central Timer module to switch off after 8 mins.
So in fact the switch only sends a ground signal to the CTM which then grounds the R18 (K164) relay for 8 mins to heat up the screen.

The indicator light in the switch is powered from F41; the illumination lamp though gets its power direct from the ignition switch (always on when driving).

The relay powers the windscreen from the Batteryplus in the Battery Junction Box over two fuses for each half, F38 and F41. It has a common ground, (splice) S123, LH A-pillar, right-hand-drive (RHD)

If the relay functions the indicatorlamp in the button should work from F41.

The 12V presence on the screen's halves can be measured from the L-R sides below the screen agianst GND.

In addition one must measure resistance from each side against GND, in the order of 5 Ohms each, to diagnose conductivity. Pull relay/fuses first!

HTH,
Ray
Title: Re: heated front screen 24v
Post by mikeb on Feb 28th, 2009, 12:15pm
Hi all,

I started a similar thread at the end of  December and thank all the members for their inputs.
I find Cosray's response of today excellent in his total description.  I gave up trying to find a simple solution as I concluded that the effectiveness of the elements had diminished to a state that a screen replacement is the only option.  The resistance reading I obtained using my very cheap analogue meter was 2 ohms.  I have been under the impression that for the heater to work the resistance should be around 0.5 ohm. Can anyone confirm this is correct?
Title: Re: heated front screen 24v
Post by Cosray - The Hague - Holland on Feb 28th, 2009, 3:07pm
Hi Mikeb,

12 V divided by 0.5 Ohms returns 24 Amps; that's a bit much for half a section, since its fuse limits to 30 A. In Watts that would return P =  V2 / R = 288 W (or 12 x24) for both halves.

12 V divided by 6 Ohms returns 2 Amps and that's probably low. P = U x I = 24 W; bit low.

But - since it is a low resistance affair anyway your reading should be around 1 - 10 Ohms; NOT anything over 100 Ohms: that would immediately indicate a broken section or bad connection.

Check for the orange LED in the centre of the pushbutton: ONLY that shows whether the CTM returned the GND signal for the relay to close, thereby feeding the 2 fuses, the windscreen and the indicator LED.

The confusing thing here is that the switch does NOT connect to the relay coil as we expect, but to the CTM electronics instead.

Mind - the illumination of the pushbutton housing is switched directly from the ignition switch. Same goes for the rear window heater, but for the timer function.

Testing

1) I remember testing the CTM:  depress & hold the windscreen heater button and switch on ignition. It's somewhere on this website; I will have a look.

2) Stick 12 V on each windscreen half while measuring current AND/OR apply Freezer Spray and watch it thaw.

Check for a proper ground contact; each ˝ Ohm contactresistance will cause a voltagedrop of 6 V and powerloss and very disturbing currentloops in the system.

HTH,
Ray
Title: Re: heated front screen 24v
Post by adamn on Feb 28th, 2009, 4:59pm
It might also be worth checking the enhanced data monitor using VE OBD2 scanner.
The EECV knows, when the driver wants the heated windscreen turned on.

It is number 63 HW (Heated Windshield is On/Off)

I guess it uses this information to expect heavier engine load (same as with AC on).
I'm also not sure, if the heating works when engine is not running.

If it will keep showing OFF (with the switch on), there might be a problem in CCM or with the wiring looms.
The sumbited CCM testing procedure is also a good idea !
Title: Re: heated front screen 24v
Post by Cosray - The Hague - Holland on Feb 28th, 2009, 5:12pm
The heated Windshield relay (K84) is powered by the Engine Run Relay (K164), so no juice/cut at standstill, as a precaution.

Pin 14 at the PCM gets the ON signal.

Ray
Title: Re: heated front screen 24v
Post by mikeb on Mar 4th, 2009, 7:00pm
I have just used a decent meter to monitor resistance through my screen. Reading with all off = 1.4 ohms.
Switched on engine and front screen heater got 14V reading to screen but no heat generated.  Switched off resistance reading now 5000 ohms.  I'm pretty sure this proves the element in my screen has gone.
The earth continuity is ok but I couldn't find the common ground behind the trim on LH A-pillar as described in Cosrays recent entry.  
Has python9 sorted anything out?
Title: Re: heated front screen 24v
Post by Cosray - The Hague - Holland on Mar 4th, 2009, 9:00pm
Your reading of 1.4 Ohms means about 10 Amps of current at 14V and that's for one half segment.

That would generate 120 Watts of heat each.
Between what points are you measuring?

The resistance reading qualifies for proper functioning so either your ground or your PLUS is missing.

Just grab 2 leads from the battery + and - clip them on and test the thing from each side, using Freeze Spray to watch it thaw.

HTH,
Ray
Title: Re: heated front screen 24v
Post by mikeb on Mar 4th, 2009, 9:38pm
Hi Ray,

Thanks for your help.  I am measuring one section between the two wires at the bottom corner of the screen.
Is the 5000 ohm reading I get after switching the system on then off proof that the attempt of heating up the screen indicates that the element can no longer cope under load?  
Title: Re: heated front screen 24v
Post by Cosray - The Hague - Holland on Mar 4th, 2009, 9:58pm
I am afraid... when you measure resistance make sure all windscreenleads are hooked off any other contacts, so floating as it were; otherwise you will get false readings.

A heater when operating from 12-14V is a very low-ohmic thing, comparable to your stereo loudspeakers...

Either you measure between say 5 and 10 Ohms or nothing -- meaning there is either sufficient conductivity to produce heat at 12-14 V OR you measure an open circuit - anything upwards from 200 kOhms to 1 MOhms, which is the same resistance that you would measure between your thumbs: leakage really.

There is no in-between at these basic circuits. This is why Grounds and proper relay and fuse contacts are so important: 0.5 Ohms contactresistance means 3-6V voltage drop equalling c. 50-100 Watts powerdrop.

If measuring is not indicative or iffy just wire up the screenhalf using a couple of wires between battery, ground and screencontacts and some Freezer spray and you will see whether it heats up.

Doing that you might include a solid Amps meter of min. 30A to measure currentflow.

HTH,
Ray
Title: Re: heated front screen 24v
Post by python9 on Mar 6th, 2009, 7:42pm
everything off inside the car unplugged the windscreen switch and the voltage when the igintion switched on and car running  i get 12v coming through the plug so there is power to the switch  so i have a dud switch
Title: Re: heated front screen 24v
Post by Cosray on Mar 6th, 2009, 10:46pm
That's good however the switch only takes that 12V (as a signal, no current/power whatsoever))  to the CCM which in turn activates the windscreen heater relay which supplies 12V power to the windscreen halves.

When the switch is properly wired and pushed does the orange LED inside the button come on?

That's proof that the CCM is correctly sending 12V to the LED and the  relay. You can see the LED and hear the relay clicking.

The relay supplies the 12V to the two halves of the heated screen via its each two 30A fuses.  

So if the switch is pressed AND the LED lights up AND the relay comes on you should be measuring 12V on both halves of the screen.

Make sure the Ground wires are well grounded.

Ray
Title: Re: heated front screen 24v
Post by python9 on Mar 6th, 2009, 11:25pm
ray the switch does'nt light up when pressed thats why i suspect the switch
Title: Re: heated front screen 24v
Post by Cosray on Mar 6th, 2009, 11:30pm
You could make sure by using an Ohmmeter between the contacts or even a simple battery and an lightbulb to check proper closing of the contacts, AND check the LED as well!

ALSO you could just exchange it for the other rear windscreen switch which is identical and test if your observation holds water.

If true, buy 2 new switches, they're equally old!

Good luuck,

Ray
Title: Re: heated front screen 24v
Post by gozz on Mar 6th, 2009, 11:31pm
python9.
The switches wont light up if the tiny bulb is bust,you need to test it on the bench with a meter or battery bulb and wire.
                                          GOZZ.
Title: Re: heated front screen 24v
Post by Highlander on Mar 6th, 2009, 11:39pm
Will test the switch theory tomorrow, John's coming for a visit, theres a couple of spare switches kicking about here ;)
Title: Re: heated front screen 24v
Post by python9 on Mar 7th, 2009, 12:15am

on 03/06/09 at 22:46:11, Cosray wrote:
That's good however the switch only takes that 12V (as a signal, no current/power whatsoever))  to the CCM which in turn activates the windscreen heater relay which supplies 12V power to the windscreen halves.

When the switch is properly wired and pushed does the orange LED inside the button come on?

That's proof that the CCM is correctly sending 12V to the LED and the  relay. You can see the LED and hear the relay clicking.

The relay supplies the 12V to the two halves of the heated screen via its each two 30A fuses.  

So if the switch is pressed AND the LED lights up AND the relay comes on you should be measuring 12V on both halves of the screen.

Make sure the Ground wires are well grounded.

Ray

no the orange led does not light up when i press the switch but it did before
Title: Re: heated front screen 24v
Post by mindofitsown on Mar 11th, 2009, 4:22pm
Has this problem been resolved since the last post (before this one)? I was following the thread with interest since only one half of my front screen heater works. Its been this way for a year or so (thus has nothing to do with a more recent thread I started regarding interior lights and BOTH screen heaters, now resolved). I've checked fuses 38 and 41 and these are fine. I presume that since only one relay is listed, it serves to provide power to two fuses which in turn serves each half of the windscreen. If I'm right, then the relay must be working otherwise both sides would be inoperative.
I'm confused about how the winscreen is connected. I can only see two connections and these are at the bottom corners (spade terminals). For the screen to operate in two halves, there must be a further connection for a common ground/common +ve supply (at least i.e. 3 wires in tota) so where is this other wire?
Title: Re: heated front screen 24v
Post by Simmo on Mar 11th, 2009, 5:00pm
At the top. Have a look atThis page (http://www.fordscorpio.co.uk/manual/windows/windscreen.pdf)  ;)
Title: Re: heated front screen 24v
Post by mindofitsown on Mar 11th, 2009, 5:44pm
Aha! Many thanks.
Title: Re: heated front screen 24v
Post by Highlander on Mar 11th, 2009, 5:53pm
new switch didnt make any difference, still doesnt light up, back to the drawing board :)
Title: Re: heated front screen 24v
Post by python9 on Mar 11th, 2009, 6:45pm
i am going to check the aux fuse box tomorrow to see to see if i have  missed  puttting a plug in the bottom of the fuse box


Ford Scorpio Forum » Powered by YaBB 1 Gold - SP 1.3.1!
YaBB © 2000-2003. All Rights Reserved.