Rex Burkheimer - WM wrote:
> I haven't done this in years, so I need a refresher. I need to pull a
> vacuum on an R-12 system ('87 VW, conventional ), then charge it with R-12
> (yes, still have 3 cases).
> How are the three hoses hooked up?
> What valves do you open when etc?
> Anybody care to take the time to walk me through it to jog my memory?
Obviously there are replies that my mail server has not
caught up to. I saw the next post from Rex where he
replied to another post, but I haven't seen the one he
is replying to. So I may be restating something that has
been said already.
That said, here goes:
I have never charged a Volkswagen or any Deutchmobile
for that matter. There may be minor differences.
You have a suction or low pressure side and a high
pressure side. Older vehicles have straight forward 1/4
inch male flare thread (MFT) fittings. Newer vehicles
have changed the size of one or more of them to keep
people from hooking up the low side to the high side.
You will need to obtain the appropriate fittings.
The low pressure line is larger (ususlly) line hooked to
the compressor. It goes directly to the Evaporator
outlet (cool gas, low pressure).
The high pressure line (hot gas, high pressure) comes
out of the compressor and goes to the inlet side of the
The Condenser outlet is piped to the receiver/drier and
then to the Evaporator inlet (warm liquid, high
pressure). If you have a sight glass it will be next to
or part of the receiver/drier. If you don't know what it
looks like, go to an auto parts store and ask to see one
for your specific model. Beer or other suitable bribes
could prove handy.
Now; some manufacturers put access fittings on all three
lines, some on only two, and ocaisionally on only one.
You absolutely need to find the low pressure side.
Inspct all the hoses and lines untill you are certain
which is which. Find the fittings.
You gage set has a blue, low pressure side on the left;
a red high pressure side on the right; and a yellow
non-valved hose in the center. If your center hose is
valved at the manifold, you have an excellent set.
The vacuum pump goes to the center hose. You want to
evacuate the system from both the high and low side
ports. This is where I would suggest leak testing with
dry Nitrogen. Any welding supply shop has it. Get a
small tank and if it doesn't have the 1/4 inch fitting,
you shouldn't have any trouble getting the right fitting
to make your connection. See www.johnstonesupply.com
for some info on fittings. Pump it up to about 100psi
and leak check with soap bubbles.
That R-12 is damn expensive. Over $35/lb in 30lb
bottles. More than I would want to use for leak
detecting. IF you were in my neck of the woods, I'd
trade you straight across, two cans, for all the labor.
Might be you could get a similar deal where you are.
Once the leaks are found and repaired, and you have a
good vacuum pulled; Set gages-- Low side valve closed;
Compressor OFF; Connect the can to the center port in
vapor charge mode. Read the can. Vapor is usually UP and
Liquid is generlly DOWN. Read the can.
Bleed air. Put the can in the liquid mode. Open the HIGH
side valve and charge untill the liquid stops flowing.
The Low side gage should be up to near the high side
pressure. Shut the High side valve. Turn on the
compressor. The Compreesor should NEVER be running when
you have the high side valve open. Continue charging
from the vapor side in vapor mode. If you couldn't get
to the high side, then charge vapor only into the low
side. It will take longer, but liquid freon into the
suction side can kill Compressors.
Check the temp differential between the inlet air and
outlet air inside the car. Rule of thumb says 25-30F
degrees. Those funny temp numbers on the gages show what
the change of state temp is at a given pressure.
Evaporating (boiling actually) from a liquid to a gas or
condensing from a gas to a liquid. The evap side must be
above 32F or freezeup will occur. Freezeup is when the
moisture in the air changes from a gas directly to a
solid (ice) on the face of the evaporator. This
restricts the airflow causeing the evap temp to drop and
more ice forms. Vicious circle ensues, leading to a
solidly blocked evap, a big hunk of ice in your evap
housing and no air flow into your ducts.
The 32F point is about 30psi or R-12, so you want to
shoot for about 40psi operating pressure at high idle or
operating RPM. High side should be in the 150psi range
but this will vary depending on ambient temp and
humidity. Condensing temp should be at least 25F above
ambient. If you have a sight glass, charge untill there
are no more bubbles, then charge untill the high side
comes up 3 to 5 psi at the same RPM.
Many systems have high pressure cut-out controls, low
pressure cut-offs, and temp sensing cut-offs. Any of
these controls can keep the compressor from running.
Blockage in the drier or metering device can restrict or
totally block freon flow. Hoses are prone to dring out
and cracking with age and dis-use. The flexible lines
are also subject to permiation. That's where the little
bitty freon molocules pass through the bigger synthetic
rubber molucules and make thier way to the atmosphere.
Not so much a problem with newer vehicles, but the newer
compounds dry out and crack sooner.
This is kind of long, but someone asked about a subject
that I actually know something about. :>)
Hope it helps.
Matt in Vancouver WA
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