Rear defroster woes

LeedomtoFreedom · 11-06-2021, 06:54 PM

Getting ends tied before winter hits.

The rear defroster does not seem to work.

Tested with a laser temp gauge and it doesn't show any change. The switch receives and sends power to the relay, the relay clicks and sends out the 12v but the filament doesn't seem to heat up. I can't directly check the filament in the window due to tint.

Need some advice before I can't see.
Thanks

283SD · 11-06-2021, 11:29 PM

What model?, if it's a wagon, check the wires at the hinges.

LeedomtoFreedom · 11-06-2021, 11:33 PM

90 240 wagon. I'll check

B3rnard · 11-07-2021, 11:05 AM

Hi LeedomtoFreedom,

Doing EXACTLY that right now, before winter. Mine's 1991 245, switch is OK, but which relay did you get to? I have 3 behind the console, of which 1 is for the turn signals.
Do you have a part# or pic from the relay in question? Cheers! B.

Hinges checked, did those this summer. Tint film also in the way.

LeedomtoFreedom · 11-07-2021, 08:03 PM

Quote:

Originally Posted by B3rnard

Hi LeedomtoFreedom,

Doing EXACTLY that right now, before winter. Mine's 1991 245, switch is OK, but which relay did you get to? I have 3 behind the console, of which 1 is for the turn signals.
Do you have a part# or pic from the relay in question? Cheers! B.

Hinges checked, did those this summer. Tint film also in the way.

It's in the drivers footwell. Mine's probably in a different location than yours since I did a manual swap and didn't remember where they went. It's not the silver headlight relay. It's a tall white box relay with 4 pins missing a central pin. When you turn the defroster on you can hear it click on.

was looking for some wiring location info since there really isn't anything I've seen.

2 old for this · 11-07-2021, 08:34 PM

Use a test light to check voltage at the grid and ohm meter for ground at the other side.

dl242gt · 11-08-2021, 01:29 PM

The Bentley manual has relay locations as does the greenbooks. Try to find a print version of the wiring diagram greenbook for 1990. They are very helpful with this kind of stuff.

LeedomtoFreedom · 11-08-2021, 06:38 PM

Okay popped off the inside bevel of the hatch window where the cable ends meet the heating element. Getting 12v to the hotside and ~.18 v on the ground side. This seems normal as the heating element is a big resistor. What gives. How long does this thing take to heat up?

283SD · 11-08-2021, 08:58 PM

From a cold start on my '90 wagon, about a 5 mile drive, by then I was at the shop that I did contract work for.

Lazarus · 11-18-2021, 12:47 PM

OK, you have determined that battery voltage is getting to the rear connector. Separate the connector (engine off) and check resistance of the heating grid. I'm guessing it should be 1 ohm or less. Typical failure points are where the wires connect to either end of the grid.
-Lazarus

11-07-2021, 11:05 AM	#4
B3rnard Newbie Join Date: Feb 2020 Location: The Netherlands	Defrost relay Hi LeedomtoFreedom, Doing EXACTLY that right now, before winter. Mine's 1991 245, switch is OK, but which relay did you get to? I have 3 behind the console, of which 1 is for the turn signals. Do you have a part# or pic from the relay in question? Cheers! B. Hinges checked, did those this summer. Tint film also in the way.

11-08-2021, 01:29 PM	#7
dl242gt Old and boxy but good. Join Date: Jun 2002 Location: S NJ, a suburb of Phila.	The Bentley manual has relay locations as does the greenbooks. Try to find a print version of the wiring diagram greenbook for 1990. They are very helpful with this kind of stuff. __________________ Dave, 1982 242 turbo. 338k miles. MVP coilovers and 3" exhaust. Flowed 405 with a V15. Cossie turbine housing with upgraded compressor housing. 90+, IPD remote oil filter. Some other goodness, too. Been lots of fun over 25 years. Restored in 2k. Now ready for a 2nd restoration. 1993 245 Classic, 440k miles, enem V15. IPD bars and chassis braces. Simons sport exhaust from Scandix. sbabbs ezk chip. Been a good road warrior. Genuine Volvo rebuilt leaky M47.

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11-06-2021, 11:29 PM	#2
283SD Board Member Join Date: Mar 2008	What model?, if it's a wagon, check the wires at the hinges.

11-06-2021, 11:33 PM	#3
LeedomtoFreedom Board Member Join Date: Oct 2017 Location: Ingleside	90 240 wagon. I'll check

11-07-2021, 08:34 PM	#6
2 old for this Board Member Join Date: Mar 2018	Use a test light to check voltage at the grid and ohm meter for ground at the other side.

11-08-2021, 06:38 PM	#8
LeedomtoFreedom Board Member Join Date: Oct 2017 Location: Ingleside	Okay popped off the inside bevel of the hatch window where the cable ends meet the heating element. Getting 12v to the hotside and ~.18 v on the ground side. This seems normal as the heating element is a big resistor. What gives. How long does this thing take to heat up?

11-08-2021, 08:58 PM	#9
283SD Board Member Join Date: Mar 2008	From a cold start on my '90 wagon, about a 5 mile drive, by then I was at the shop that I did contract work for.

11-18-2021, 12:47 PM	#10
Lazarus Board Member Join Date: Jan 2005 Location: Seattle, WA	OK, you have determined that battery voltage is getting to the rear connector. Separate the connector (engine off) and check resistance of the heating grid. I'm guessing it should be 1 ohm or less. Typical failure points are where the wires connect to either end of the grid. -Lazarus