Date:         Sat, 23 Oct 1999 15:40:32 -0400
Reply-To:     David Beierl <dbeierl@IBM.NET>
Sender:       Vanagon Mailing List <vanagon@gerry.vanagon.com>
From:         David Beierl <dbeierl@IBM.NET>
Subject:      Re: Heater fan switch
Comments: To: Per Lindgren <lindgre@ONLINE.NO>
In-Reply-To:  <3811EABC.925E9E94@online.no>
Content-Type: text/plain; charset="us-ascii"; format=flowed

At 13:05 10/23/99 , Per Lindgren wrote:
>I dissected the old switch, and it was melted solid. I don't know what caused
>this, but the fan ran much better with the new switch than it did with the old
>switch. If another meltdown happens, I guess I will have to investigate
>further.

I know!  I know!  The switch is made (thank you VW) of thermoplastic, and
carries 12 amps.  When it gets a bit of contact resistance the contacts
heat up, the plastic gets soft, the movable contact presses the fixed
contact down into the soft plastic -- voila, it has just built itself a
little playpen.  The contact pressure is less, the resistance is more, the
contact gets hotter yet...

I *love* relays...my switch on high speed is now supplying all of 100 ma or
so to power a relay that feeds the fan from a dedicated circuit.  At lower
speeds it has no trouble driving the fan itself.

david
David Beierl - Providence, RI
  http://pws.prserv.net/synergy/Vanagon.htm
'84 Westy "Dutiful Passage"
'85 GL "Poor Relation"