[Vwdiesel] AC woes

Val Christian val at swamps.roc.ny.us
Sat Aug 2 14:54:39 EDT 2003

> In a message dated 8/2/2003 5:21:15 AM Pacific Daylight Time,
> val at swamps.roc.ny.us writes:
> > Generally, your low side shouldn't drop below
> >  20 and should not be above 35 or so.
>   That's what I always liked and thought as well but a lot of systems are
> undercharged at that pressure level.  They often need 40 to 50 psi at a
> high idle, to maintain good efficiency.  The discharge air is a tad warmer
> but it's steady rather than fluctuating as the compressor cycles.  Some
> systems kick out at about 28 psi so as soon as you hit the highway, it's
> cycling if you have around 30 psi.  :P
>      Loren


I didn't think through the qualified answer process.  You're absolutely
right.  A properly charged system will run 40 or more PSI running down the
road with the AC running.  I was thinking about standing outside the
car, with the engine idling, in front of the gauges.

You are also right about systems kicking out when the pressure drops below
a low pressure switch on the inlet side.  That is why I mentioned to Nate
that the cycling on a slightly overcharged system can be less than on a
properly charged system (for example, by weight).  Isn't anyone on the
group a refrig tech, who can authoritatively set us all straight?  It would
be great!

If you get frost on the evaporator, the pressures will climb rapidly.  I've seen
this operating aircraft with mission specific air conditioning equipment,
in warm and humid settings.  The nice thing, is that these systems are
a bit higher priced, and often have instrumentation.


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