Date: Sat, 21 Feb 2009 20:04:22 -0600
Reply-To: Jim Felder <jim.felder@GMAIL.COM>
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Jim Felder <jim.felder@GMAIL.COM>
Subject: Re: Where does this relay go?
In-Reply-To: <4d1b79350902211802k315bdbebt2c2b9517ef055414@mail.gmail.com>
Content-Type: text/plain; charset=ISO-8859-1
And another thing about my instrument cluster that should be reported
to the Society for Short-Lived Phenomenon is that some months back I
had the turn signal indicator LED working for about a minute.
Jim
On Sat, Feb 21, 2009 at 8:02 PM, Jim Felder <jim.felder@gmail.com> wrote:
> David, it's a 1983 diesel.
>
> Jim
>
> On Sat, Feb 21, 2009 at 7:51 PM, David Beierl <dbeierl@attglobal.net> wrote:
>> At 08:13 PM 2/21/2009, Jim Felder wrote:
>>>
>>> the coolant light blinked slowly at first, but as the engine heated
>>> and the temp needle rose, the blinking became more and more of a
>>> constant red light until, at needle center, it was on full time. When
>>> I reached my destination, I turned it off and restarted and it was
>>> fine ever since.
>>
>> Fascinating. I've never heard of like behavior. What year is this beast?
>>
>>
>>> I don't know what's in the control module, but I doubt that it is
>>> really a relay...
>>
>> It's not. It's a rather fancy circuit that sends a very high-impedance
>> (weak, if you will) square wave out on the active level sender terminal. If
>> that square wave is tied to any constant level between ground and +12
>> through a resistance of about 180K or less it will be quenched, and the
>> gauge driver remains inactive and floats with the temp sender output.
>> However if the square wave continues for several seconds without being
>> quenched, the gauge driver goes active and pulls the sender line down to a
>> level corresponding to an overheat condition (not all the way to ground,
>> which would burn up the gauge). That triggers the flashing light in the
>> gauge, which flashes for several seconds whenever it's triggered (and it's
>> this behavior that gets out of hand inside the gauge and leads to constant
>> flashing for no cause).
>>
>> At this point the old (large) and new (small) controllers part company. The
>> old one applies a steady overheat signal until the square wave can
>> reestablish itself, which drives the needle into the hot zone. The new one
>> applies an intermittent signal which keeps triggering the blinker without
>> greatly affecting the gauge reading. The new one also latches on, so the
>> blinking will continue until key-off regardless of what the level sender
>> sees.
>>
>> I had a lot of enjoyment tracing out and analyzing the interior circuit of
>> the old-type controller. It was cleverly done. I haven't seen inside the
>> newer one, but I suspect they put things into a single no-doubt-proprietary
>> chip that were wired out on the old one, since the new one is half the size
>> and does more.
>>
>> --
>> David Beierl - Providence RI USA -- http://pws.prserv.net/synergy/Vanagon/
>> '89 Whitestar "Scamp"
>>
>
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