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Topic: heated front screen 24v (Read 2538 times) |
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python9
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1997 24v ghia saloon
 
Posts: 241
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heated front screen 24v
« on: Feb 17th, 2009, 6:42pm » |
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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
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gozz
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Re: heated front screen 24v
« Reply #1 on: Feb 17th, 2009, 7:40pm » |
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python9.
Could you have knocked a connector off the bottom of the screen in the maul 
GOZZ,
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gost
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I'm a YaBB newbie!
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Re: heated front screen 24v
« Reply #2 on: Feb 17th, 2009, 7:44pm » |
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When mine didnt work it was a relay
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2.3 ultima
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Snoopy
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Very old.BAD tempered and missing friends.
Posts: 6278
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Re: heated front screen 24v
« Reply #3 on: Feb 18th, 2009, 6:54pm » |
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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.
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python9
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1997 24v ghia saloon
Posts: 241
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Re: heated front screen 24v
« Reply #4 on: Feb 18th, 2009, 7:13pm » |
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on Feb 17th, 2009, 7:40pm, gozz wrote:python9.
Could you have knocked a connector off the bottom of the screen in the maul
GOZZ, |
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where are the connections gozz
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gozz
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Re: heated front screen 24v
« Reply #5 on: Feb 18th, 2009, 8:12pm » |
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Right in the corners of the screen,under the bonnet,just outside the edge of the plastic grille.
GOZZ.
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python9
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1997 24v ghia saloon
Posts: 241
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Re: heated front screen 24v
« Reply #6 on: Feb 19th, 2009, 2:12pm » |
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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
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python9
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1997 24v ghia saloon
Posts: 241
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Re: heated front screen 24v
« Reply #7 on: Feb 19th, 2009, 9:20pm » |
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tried another relay still not working
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Cosray
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8th Scorpio, 2nd Cosworth: currently '95
Posts: 569
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Re: heated front screen 24v
« Reply #8 on: Feb 28th, 2009, 8:20am » |
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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
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mikeb
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I love YaBB 1G - SP1!
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Re: heated front screen 24v
« Reply #9 on: Feb 28th, 2009, 12:15pm » |
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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?
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Cosray
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8th Scorpio, 2nd Cosworth: currently '95
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Re: heated front screen 24v
« Reply #10 on: Feb 28th, 2009, 3:07pm » |
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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 ½ Ohm contactresistance will cause a voltagedrop of 6 V and powerloss and very disturbing currentloops in the system.
HTH,
Ray
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adamn
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adam+n
Posts: 34
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Re: heated front screen 24v
« Reply #11 on: Feb 28th, 2009, 4:59pm » |
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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 !
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Cosray
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8th Scorpio, 2nd Cosworth: currently '95
Posts: 569
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Re: heated front screen 24v
« Reply #12 on: Feb 28th, 2009, 5:12pm » |
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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
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mikeb
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I love YaBB 1G - SP1!
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Re: heated front screen 24v
« Reply #13 on: Mar 4th, 2009, 7:00pm » |
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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?
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Cosray
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8th Scorpio, 2nd Cosworth: currently '95
Posts: 569
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Re: heated front screen 24v
« Reply #14 on: Mar 4th, 2009, 9:00pm » |
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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
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mikeb
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Re: heated front screen 24v
« Reply #15 on: Mar 4th, 2009, 9:38pm » |
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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?
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Cosray
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8th Scorpio, 2nd Cosworth: currently '95
Posts: 569
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Re: heated front screen 24v
« Reply #16 on: Mar 4th, 2009, 9:58pm » |
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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
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python9
Full Member
1997 24v ghia saloon
Posts: 241
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Re: heated front screen 24v
« Reply #17 on: Mar 6th, 2009, 7:42pm » |
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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
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Cosray
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8th Scorpio, 2nd Cosworth: currently '95
Posts: 569
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Re: heated front screen 24v
« Reply #18 on: Mar 6th, 2009, 10:46pm » |
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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
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python9
Full Member
1997 24v ghia saloon
Posts: 241
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Re: heated front screen 24v
« Reply #19 on: Mar 6th, 2009, 11:25pm » |
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ray the switch does'nt light up when pressed thats why i suspect the switch
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