From: John De Armond
Subject: Re: do it yourself
Message-ID: <37A9CB1B.D6CDA2F5@bellsouth.net>
Date: Thu, 05 Aug 1999 13:32:02 EDT
Newsgroups: sci.engr.heat-vent-ac

David Threlkeld wrote:
> 
> On 20 Jul 1999 01:13:34 -0400, Allan Adler <ara@zohar.ai.mit.edu>
> wrote:
> 
> >Suppose that the interior of a glove box needs to be very cold but
> >you don't want the room that the glove box is in  to be that cold.
> >How do you design such a glove box? (I realize this depends on the
> >temperature one wants).
> >
> >I don't assume that there is a commercial solution to this problem,
> >although it wouldn't surprise me. It would surprise me if I could
> >afford one, though.
> 
> There is a very simple but expensive solution to this one.... wait for
> BMW to mass produce thier latest proto type car. It has and air
> conditioned glove box that stays at either 34 or 43 deg F I dont
> remember which one it was.

Damn, another missed opportunity.  I knew I should have patented the
idea when I built a refrigerated glove box into my then-new '75
280Z.
> 
> Now for the big question... WHY? hehe my maps dont care if its hot or
> cold lol.

Yeah, but your beer does. :-) Er, in these PC days, I meant "soda".

How to do it is easy.  Most modern AC systems run the AC part to
achieve a set evaporator temperature, usually near freezing, and
then set the cockpit temperature by tempering the air with either
heat or outside air or both.  Evaporator temperature control is
pressure control either by POA valve, etc or compressor clutch
cycling.  In either system, the compressor operation follows heat
load.

Knowing this, the solution easily follows.  Simply set up another
expansion loop in the glove box.  When I did my Z-car box, I coated
the outside of the box with aerosol insulating foam (good stuff or
equiv) and formed 1/4" copper tubing to conform to the inside of the
box, arranging a couple of paths.  Tapped off the liquid line to a
new expansion valve and brought the evap exhaust back to a tee in
the compression suction line.  If your system has a POA valve (GM's
name - goes by many other names), even better.  If you tap your
suction downstream of the POA, you can achieve a much lower
temperature in the glove box than possible when running at the AC
evap pressure.  If you need the box not to freeze, use a POA valve
(also known as a backpressure regulator) on the glove box to control
the minimum pressure and thus the lowest possible temperature.  This
is much simpler and much more responsive than trying to do it with a
thermostat.

This is REALLY handy.  In addition to beverage storage, other
opportunities arise.  I used to do a lot of pro photography.  Pro
film needs to be refrigerated.  instead of having to lug around an
ice box like most photogs, I simply plopped the film in the glove
box.  Would leave the engine running on location so the goodies
would stay cool.  This is one of those things that you never
realized you needed until you had it and then you can't live without
it.

John