Date:         Sat, 7 May 2016 19:56:21 +0000
Reply-To:     gary hradek <hradek@YAHOO.COM>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         gary hradek <hradek@YAHOO.COM>
Subject:      domestic fridge light always on flame indicator light always on
Content-Type: text/plain; charset=UTF-8

 At 03:02 PM 5/4/2016, gary hradek wrote:
>David,
> Would you have any idea why the flame indicator light on
> the fridge of my 87 westy is always on even when the fridge is not
> being cooled?
> thanks gary

Hi Gary,

Unplug the separate black wire coming from the LED panel plug -- it's
the connection to the thermocouple on the fridge and plugs into the
fridge harness, the other end of the connection plugs into the back
of the gas valve where the thermocouple is. If the light goes out
then the panel is probably ok and I'd start by investigating fridge
ground and other wiring. (If it's only lighting when the engine
runs, no doubt you have DC cooling turned on, this often lights the
flame light.)

If it still lights with the wire unplugged chances are the righthand
LM324 chip is bad (each chip has four amplifiers, the left one does
the water lights and a spare amplifier, the right one does power and
flame LED). Those chips have not been robust in this circuit and
other than solder fatigue at the little switch almost all the board
problems are failed chips. Radio Shack plus any real electronics
outfit like DigiKey have LM324 chips.

Yrs,
d

>David,
> There was very litle information about
> this problem in the vanagon data base when I did a search.
>If it is ok with you may I enter your
>explanation into the vanagon list so that it is available to others?
>As always the information you provided was most
>useful. When I tried to remove the LED Panel
>the light went off so I pushed it back in and
>tested it and it is working like it should.
>Light goes out when the fridge is not cooling
>but comes on when it is cooling. I am sure
>there is some problem I have yet to fix but will
>wait until the problem becomes permanent.
>Lately my way of testing if the fridge was on
>was to sniff the exhaust vent. One last
>question, Is the black wire coming from the
>thermocouple putting out enough current that it
>could me read with some sort of volt
>meter? can I forward this information on to
>the vanagon list if you do not? Gary
--
David Beierl -- dbeierl@attglobal.net

Yes, you can read the thermocouple with a
voltmeter on the 200 millivolt scale. It's the
only voltage in the van (possible exception of
the ignition high voltage) that's deliberately
negative to chassis ground. It's only a fraction
of a volt but has very low impedance, so it can
drive enough current through a dozen or so turns
of heavy wire to make a magnet that with
carefully machined pole pieces can hold the gas
valve open while the flame is lit. The op amp
for the LED has a programmed gain of around -350
IIRC (the gain is set by the ratio of the
feedback resistor to the input resistor).