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iBoaterer[_3_]

In article ,
says...

On Tue, 11 Jun 2013 08:21:14 -0400, "Eisboch" wrote:

"Hank©" wrote in message
eb.com...

On 6/10/2013 9:37 PM, wrote:

You still don't know where the gas went. You will be back.

About 3 mos. ago I had exactly the same scenario as Eisboch, including
the difficulty getting the compressor to start. Over several years,
the
charge can leak past the seals. Mine has been working fine since the
recharge. Knock on wood.

-----------------------------------------------

The seals that typically go bad are simple Buna or Viton O'rings.
They are not perfect seals, even when new. They have a specification
called "permeability" that relates to how many molecules can pass
through the material it's made of. Dealt with this routinely in the
high vacuum equipment business. Assuming no real "leaks", the
permeability of the various O'ring seals used on the vacuum system is
what limited the ultimate level of vacuum that could be achieved. In
ultra high vacuum systems, use of Buna or Viton O'rings are used
sparingly and compressed copper metal seals are used instead.

One of the features of the 134A refrigerant that replaced freon 12 is
that the gas molecules are smaller and the number of molecules that
can pass "through" the O'ring material is higher. If the O'ring is
kept lubricated (contained in the 134A refrigerant), the amount lost
due to permeability is reduced. But if the system sits, unused for
lengthy periods of time, enough can pass through the O'ring seals to
make the system inoperable.

I think the old Freon 12 systems had a high pressure cut out that
disengaged the clutch, causing the system to cycle on and off in
normal operation. What appears to be new in the more modern systems
is a transducer that also monitors the low side pressure side. If it
drops too much, the clutch will not engage. It's purpose is to
prevent damage to the compressor by running it "dry". I am not an AC
expert by any means but it makes sense to me.

Car AC units have had a low pressure cut out for years. My 83 Firebird
had it.
It took 2 cans of gas to get it going from empty.

My father had a '70 Merc that had a low pressure cut out on it.