[Vwdiesel] AC woes

Val Christian val at swamps.roc.ny.us
Sat Aug 2 09:56:34 EDT 2003

The only method better than using gauges is to evac the system, and then
recharge with a known mass of coolant. I suppose that's the right way.

Actual manifold gauge pressures are influenced by ambients, and by
evap and condensor temperature differentials.

It's a shameless pitch, but my handy passive IR gun is the bees knees
in debugging AC problems.  You can scan temps across a condensor, look at
temps before and after expansion blocks, and look at surfaces before and
after the evaporator to get inlet and outlet temps.

I've often told myself that if I ever built a car, I'd add sensors to
give temps and pressures for the AC.  And I'd find a way to use R-12 instead
of R134a.

When the temps are higher, the pressures will be higher.  There are tables
which will give you guidance.  Generally, your low side shouldn't drop below
20 and should not be above 35 or so.  High side is the critical side, and
I'd say 260, with the fan running and a 90F day.

Pressures also change with compressor age, drier condition, traces of
moisture in the system, etc.  I am not a refrigeration technician.

One PhD friend of mine came by after charging his car one day.  Talking about
how great the system was working.  Since my gauges were out, we hooked them
up.  The system was WAY too overfilled.  The high side gauge pegged out
immediately at 500 PSI.  The car was shut down and we recovered a couple of
pounds of refrigerant that didn't have to be there.  He was lucky nothing
blew on the way to my house.  But it sure was cold!


>   Huh???  Guess I've learned and been doing it wrong all these years.  ;-)
> There are many things you can ONLY tell with gauges.
>   If the system is over full then the low side line will be freezing up all
> the
> way, or nearly all the way to the compressor.  High side pressures will
> be on the order of 300 + PSI as well.  Too low and the low side drops
> below about 20psi and the compressor kicks out until it hits about
> 50 again.  When the high side hits 250 or 270 (can't remember which)
> the high speed of the rad. fan will come on.
>   If the expansion valve/screen is plugged or icing up then the high side
> will really climb but the low side will drop and take a long time to
> equalize.

More information about the Vwdiesel mailing list