[Vwdiesel] off topic: air conditioning

Sun Sep 2 00:15:11 PDT 2012

My experience parallels Loren's in that the times I have paid dearly to have
the A/C fixed, maybe 50% of the time it is done well, for an 800 buck
service trip usually, by a first year apprentice that really doesn't
understand how the stuff works either, so parts get replaced, freon wasted,
until the bill is large enough to ensure it works again.
I farm, have lots of things with glass cabs (greenhouses) that cannot be
used without the A/C working. It prompted me to buy a Robinaire
recovery/reclaim/recharge unit that has more than paid for itself in two
years, and forced me to learn how to do this stupid stuff myself.
It all boils down to basics, and really simple once you understand.
Freon leaves the condenser (in front of the rad) in liquid form, through the
receiver/dryer (really a filter and dessicant), to an expansion valve near
the evaporator core (inside the passenger space). Here, the valve has an
orfice that allows the freon to go from a liquid at high pressure, to low
pressure, where it evaporates to a gas and absorbs heat in doing so. This is
what removes the heat from the air you are conditioning. The low pressure
freon gas now goes back to the pump, where it is pressured up to 150 to 250
psi (depending on the system) and sent to the condenser in front of the rad,
where it loses it's heat, and goes back to a liquid.  
There are one or two limit switches.  
Low limit switch in the low pressure line that goes back to the pump-  When
the pressure is too low, the switch opens to protect the pump from having
nothing to pump. It can be too low from insufficient freon in the system, or
a plugged expansion valve will not let refrigerant flow through the
evaporator to get to the low pressure side. (sometimes the dessicant bags
break in the receiver dryer, and silica gel pellets go through the system,
stopping at the orfice in the expansion valve.  That sucks, which brings us
to the reason for a high limit switch.  The high limit switch opens when the
high pressure side of the circuit gets too high so you don't blow a line,
for instance when the desssicant bag breaks. (happens a lot on equipment
that bounces around a lot it seems). WIthout it, the pump could run until it
blows a line.
So what happens electrically, is the thermostat in the cab sez it's too
warm, sends power to the pump. The wire from thermostat goes through usually
the low switch, and the high switch, then to the pump clutch. Sometimes
there is no high limit switch, just a low, but a single use pressure relief
valve in the high side line (R12 systems mostly).
So, to diagnose without gauges to hook up and actually see what the
pressures are as the system runs...
with car running, a/c on full, look for pump clutch action. If it turns then
quits, figure out why- test the high and low pressure switches to see if one
or the other is not letting current through.  If it's high side, take it to
a shop for service unless you can recover your own freon, cause it's going
to have to come apart.  Usually it's low- the pump runs until the low side
switch shuts off to protect the pump from trying to pump vacuum. You can add
safely on the low side (blue cap) from those cheapie cans you buy at the
quickie mart until the low side switch stays shut and there is sufficient
freon for the system to run, and your a/c blows cold, under 50 degrees on
high usually.  
Look for dirt stuck to connections, it's an indication of system leakage-
the oil in the system gets out as the freon leaks out, and dust sticks to
the area.  
With flashlight, look at the little clear window on the receiver-dryer.
When the pump starts, you should see a whoosh of small bubbles, then mostly
liquid going by. If you see what looks like foam, that is a visual
indication that the system is low too.

There is no replacement for having gauges, and knowing exactly what the
system runs for pressures when it is charged exactly correctly. My robinaire
unit recharges to 1 gram accuracy, and these new systems use very little
freon- 600 grams as opposed to 7 to 8000grams in the older systems. A 600
gram system will work like junk when off as little as 50 grams. The old ones
would work if you added it with a bucket.

Important- wear safety glasses when working on systems containing
refrigerant.  A blown line in the face will freeze your corneas, and you
will be blind, period.
Good grief, that got wordy.
-james

-----Original Message-----
From: vwdiesel-bounces at vwfans.com [mailto:vwdiesel-bounces at vwfans.com] On
Behalf Of lbaird119 at aol.com
Sent: September-01-12 10:08 PM
To: pila47 at yahoo.com; val at valchristian.com
Cc: vwdiesel at vwfans.com
Subject: Re: [Vwdiesel] off topic: air conditioning

W go OT all the time especillay when it's slow...
Not working is one of those terms like bring a car in and saying it "doesn;t
run."  Doesn't start, starts but won't run, dies when you put it in gear and
so on...
  If it's a low charge then the compressor will run but only briefly, then
the clutch will cycle as the pressure pulls down too low, shuts off,
equalizes then starts over again.  It's possible to blow the safety "fuse"
and discharge the whole system.  Had that happen once.
  If the compressor won't run at all then it's either no power to the clutch
or a bad clutch.  Again, there are things in between the power source and
the clutch itself.  
  It could also be running and just doing squat, which could even be a
vacuum leak causing the proper flaps not to,  well, flap.  :-)

  It's probably relatively simple so don't give up so easily.  I found that
the "best" A/C shop in town did nothing other than cost me about $500 and
NOT fix my system!   It took me about 1 1/2 hours and $125 to do it myself
and it lasted for years.  Still have another to fix or my wife will kill me!
      Loren

-----Original Message-----
From: peter blake <pila47 at yahoo.com>
To: Val Christian <val at valchristian.com>
Cc: diesel <vwdiesel at vwfans.com>
Sent: Sat, Sep 1, 2012 6:35 pm
Subject: Re: [Vwdiesel] off topic: air conditioning

Val,
  I don't consider AC stuff too much off topic either, I did use the off
topic label so that the guys who r just interested in diesel stuff can dump
the email if they like.
  So I went out and the only electrical connection I could easily access was
a three pin connector on one of the hard lines. It did not have any voltage.
  I have noticed that the AC might not have been blowing as cold as I would
like. Getting the charge checked was on my list of stuff to do.  If I
understand this system correctly, insufficient refrigerant will activate a
pressure switch that then won't allow the system to operate.  I am not going
to pursue this further as everything on this engine is buried under covers
and hoses etc.
I think I would just rather spend the money this time.
Peter
--- On Sat, 9/1/12, Val Christian <val at mongo.mongobird.com> wrote:

> From: Val Christian <val at mongo.mongobird.com>
> Subject: Re: [Vwdiesel] off topic: air conditioning
> To: "peter blake" <pila47 at yahoo.com>, vwdiesel at vwfans.com
> Date: Saturday, September 1, 2012, 5:27 PM Was the AC anemic in the 
> morning?
> 
> Wondering if there is a marginal charge.
> 
> A frequent failure, for me, is that the AC clutch goes as the 
> compressor gets more hours on it.
> 
> I would pull the cable to the clutch, and see if it gets 12V when you 
> think the AC should come on.
> 
> 
> Report back. And we can discuss the next step alternatives.
> 
> 
> Also, I don't consider AC off topic.
> 
> > 
> >   I'd like to call on the collective
> wisdom of my fellow
> > listers to help me solve an air con problem.
> >   Yesterday morning I drove my 01 Jetta
> and I had air con.
> > In the afternoon I drove the car and no air!  I'm
> pretty
> > sure it died either at start up or shortly thereafter.
> >   I've checked every single fuse in the
> panel on the side of
> > the dashboard; they were all good. Is there someplace
> else I
> > can look and make an easy repair before I bring it to
> someone?
> > This is one of those areas of automobile operation that
> I don't
> > really feel comfortable trying to do my own repairs.
> > Peter
> > _______________________________________________
> > Vwdiesel mailing list
> > Vwdiesel at vwfans.com
> > http://www.audifans.com/mailman/listinfo/vwdiesel
> > 
> 
> 
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