Old Library

Hi Shawn

You didn't tell us the year of your car so we don't know the type of system or the refrigerant. But it is
probably R134. These systems do not have a sight glass. Charging is done by pressures. The fact that your
clutch engages tells us that at least some refrigerant is in there. With the A/C on and a 1500 rpm idle feel
the two lines coming out of the TXV (a block of aluminum in engine compartment next to the firewall on
passenger side.) The small line should be quite hot and the large line very cold, maybe frosty cold. If this
is true the A/C is working and your problem is the blend doors (controls mix of cold A/C air and hot heater
air) This is controlled by pneumatic controller. Explained in Bentley.

To go beyond above you need a set of gauges to analyze things and a vacuum pump to repair things. These two
are absolute minimum. Add a leak detector and you can do anything.

There are a lot of advantages to DIY A/C repair but you must have a few of the tools. All legal restrictions
are on professionals, none for DIY.

LOL Eric
85 GTI with VR6 Power 

You have to find out which sensor is shutting off the power to
the clutch.  That will give you a big clue to the problem. Problems
can be mechanical like the drain on the evaporator is plugged with
a leaf, water collects in the case and freezes up.  A/C shuts off
until ice melts. Or there is a little water vapor in the refrigerant
and it freezes in the expansion valve, high side pressure goes way
high and over pressure switch shuts off clutch. let it sit a while
& ice melts, start all over.  Ideally you would hook up a set of
gauges and see what is going on. Lacking gauges the best first
step is to find out which sensor is turning off the clutch power.
Go from there.

Eric
85 GTI with VR6 

Your A/C is cutting out, because it is low on
refrigerant, you might have a leak somewhere.
Your going to need gauges, gas, some leak detection
equipment.  Your going to need these tools at the
minimum, I think your better off taking it to a repair
place.

Gauges = 140$
Gas = 20$
Knowing how to use these = $$

Beware of servicing the a/c system yourself.  The refrigerant is
poisonous and heavier than air so if you have a big leak do not lay down
on the ground under the car for a better look.  You might not get back
up.
Also, if the refrigerant contacts your skin you will probably lose it
due to instant frostbite.  

If you're determined to do it yourself then prepare yourself by reading
what you can about your particular system, it's refrigerant type, and
what precautions should be taken to avoid an accident.  It isn't hard to
do but shouldn't be taken lightly.

-jt

Or...
You could buy the hose that goes between the AC system and the can of R134a
and a can or two of R134a.  Start your car and crank the AC to maximum.
Connect the hose to the can of R134a and then to the AC system on the
passenger side near the firewall--it only fits in one place.  Open the valve
by the can, hold it upside down and shake it a couple of times while it goes
into the system.  Disconnect the hose from the car when it is empty.  Then
you can see if your AC works better--is it cooler?  Does it still shut off?
That should get you colder air and an idea if it is a shortage of coolant
causing it to shut down.

2 FWIW's
1) The Bently flat out says not to re-charge your AC system but I can't see
why because it is not visibly different from any other modern system and I
have added to mine for the last three years.
2) I have never heard of an AC system shutting down from a lack of coolant.
It seems like it would run but not any cooler than the outside air. But I am
NOT an AC Tech.

Scott
Anybody want to buy a cold blowing freshly charged DE?
I am down to $7,500.00 and it won't go any lower!

The problem your talking about is called shortcycling,
the shortage of gas, the compressor will run until it
reaches normal operating pressures, when will continue
to drop till it cutouts.

Yes our cars have HIGH AND LOW pressure cutouts, and a
pressure relief valve, these are standard items found
on an air conditioning system.  

You can jump the safety switch, at the bottom of the
right fender well, there is a 4-wire switch pressure
switch there, connected to a small silver cylindrical
tank.  I am not sure of which of the  2 wires it is
off hand.  

I've heard rumors that most automtive A/C systems have a pressure sensor
that keeps the compressor from kicking on if the freon is out.  If this
is true, is there a way to trick this sensor so that I can check that
the compressor and associated electronics actually work?
I'd like to narrow down the possible faults for a borked a/c system.
Thanks,

Travis

Yes you can.  Its a switch typically with a 2 prong plug on the dryer or somwhere on the high pressure
line.  Pull it out and short the wire together, the A/C clutch should engage.

Bill

Bill, isn't the "low freon" switch on the low pressure side?  Are you thinking of the
"overpressure" switch, usually on the high side??

You are correct....:-)

Follow the low pressure line from the compressor (larger line), and look for a fitting with a
"switch" device with a couple of wires coming from it.  It may be anywere, but not in the stuff in
front of the radiator (hi-side).

Usually the device is a switch which 'opens' when pressure is too low (normally closed).  Determine
this by checking the voltage on each side (wire) of the switch (check voltage with respect to
ground, when the a/c is powered on).  You may have to stick a needle into a wire as a contact
point.

If the voltages are different (0 volts vs 12 volts),  try shorting the two wires together.  If
there is a removable connector, then you might be able to remove it and jumper the wires in the
cable together.  This should enable the compressor clutch.

This test might work even with the engine not running, but the ign ON, which is safer.  You should
hear the compressor clutch "clunk".

Don't leave it on too long if the system is empty, as there can be damage.

They almost all have a low pressure sensor that shuts off the system to save
to compressor if pressure is too low.  It is usually on the accumulator if
your system is that design (typical Ford and GM and many others).  The trick
you want is to disconnect the plug and jump the two leads on the plug
together.  Do it briefly.  If the freon is gone, so is most of the oil for
the compressor.

Some systems also have a high pressure sensor to avoid overcharge.  System
will come on but will cycle rapidly.

Gregg