Adding Compressor Lubricating Oil; Evacuating The System - Aston Martin DB7 Workshop Manual

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Air Conditioning
General System Procedures
Evacuating the System
This process, the removal of unwanted air and moisture, is critical to the correct operation of the air conditioning
system. The procedures depends on the characteristics of the recovery-recycle-recharge equipment and must be
carried out exactly in accordance with the manufacturers instructions.
Moisture can be highly destructive and may cause internal blockages due to freezing, but more importantly, water
suspended in the PAG oil will damage the compressor. Once the system has been opened for repairs, or the
refrigerant charge recovered, all traces oi moisture must be removed before recharging with new or recycled
refrigerant.
Adding Compressor Lubricating O i l
Oil can be added by three methods, two of which are direct into the system
• via the recovery-recycle-recharge station
• by proprietary oil injector.
Equipment manufacturer's instructions must be adhered to when using direct oil introduction.
The third method may be required because of rectification work to the existing compressor, or the need to fit a new
compressor. From an existing compressor, drain the oil into a measuring cylinder and record the amount. Flush the
unit out with fresh PAG oil and drain thoroughly. Refill the compressor with the same amount of PAG oil that was
drained out originally and plug all orifices immediately ready for refitting to the vehicle. The transit lubricating oil
must be drained and discarded from a new compressor before it may be fitted. An adjustment should be made to
the system oil level by taking into account:
• the quantity found in the original compressor
• the quantity deposited in the recovery equipment oil separator from the charge recovery operation.
Typically, 80 ml can be drained from the original compressor and 30 ml found in the oil separator; the sum of these
volumes (80 + 30 = 110 ml) is the amount of fresh PAG oil that must be put into the new compressor prior to fitting.
Hote: The discrepancy between this figure and the nominal capacity of 135 ml is caused by normally not recoverable oil being
trapped in components such as the receiver-drier or evaporator.
The above statements are only true if there is no evidence of a leak. Where a leak has been detected and rectified,
the compressor must be refilled with the specified quantity.
Caution: Always decant fresh oil from a sealed container and do not leave oil exposed to the atmosphere. PAG oil is very
hygroscopic (absorbs water) and rapidly attracts atmospheric moisture.
PAG oil must NEVER be mixed with mineral based oils.
Do not reuse oil following a recovery cycle, dispose of it safely.
Depending on the state of the air conditioning system immediately prior to charge recovery and the rate of recovery,
an amount of oil is drawn out with the refrigerant. The quantity is approximately 30 to 40 mi; this may vary, and
the figure is given only for guidance. It is most important that the oil separator vessel in the recovery equipment is
clean and empty at the start of the process so that the amount drawn out may be accurately measured.
May 1996 8-13