Re: A/C recharge questions

[walter@quattro.corp.inmet.com (Walter Meares)]

> > Why the Bentley recommends to evacuate system before recharging?
> 
> This procedure applies to *all* conventional air conditioner systems using 
> refrigerant under vacuum.  If you wish to successfully charge one of these 
> systems, it is *absolutely* essential to pump out the remaining refrigerant
> under vacuum, or you *will* get air in your system, and lose the ability
> to cool.

True if the system has been completely discharged.  Evacuation removes the air
and helps boil out the moisture.  Systems that have been open for a long
period of time should probably get a new drier, as well.

Moisture in an R12 AC system combines with freon to create hydrochloric acid.
This eats the system components and results in damage and contamination that
is difficult to fix without replacing every component in the system.

> 
> > Is it possible just to add a pound of refigerant ?. 
> 
> No, (well, yes, it is possible, but not it you want the system to function
> correctly afterwards.  see above.)

If the system is just low on refrigerant, R12 can be added without evacuating
the remaining charge.  However, it's expedient and socially responsible to 
find out why its low, and have any leaks fixed.  In fact, a shop will insist
on this, as they are bound by recently enacted legislation.


> 
> > oil needs to be added while adding refrigerant?

The oil level in the compressor crankcase can be checked with a dipstick
designed for that purpose.  This usually requires discharging the system,
although some systems have valves to isolate the compressor, allowing the
check to be made without emptying the system.  This is the right way to check
the oil.  If the 5000 uses the GM system, it probably has to be discharged to
check the oil.  If you know there's been an oil loss, like from a burst hose,
some oil can be added during the recharge, but its just a guess.

I must stress that working on AC without the proper knowledge and tools is
*DANGEROUS*.  Running systems have high side pressures of 200-300psi (not 
something you'd want to get hit with should a hose or tube break), the
freon/oil mix is flammable, and burned freon yields phosgene gas, a poison. That
is beside the usual hazards of working on/around a vehicle with hood open and
engine running.  

No flame intended here, but your questions are pretty basic, and the Bentley
manual and quattro list advice are not going to provide sufficient background 
to do any significant work on an AC system.  I'd advise that if you don't have 
someone  experienced to help you, for your own safety and peace of mind,  that 
you take the car to a shop.

> Bart Chambers

Walter

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