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MSC4000 - MSC15000 USER GUIDE
8.
For the Refrigeration Technician
Parker Airtek recommends that only qualified and experienced refrigeration mechanics do repair work on
these units. This section is a list of hints and instructions for the skilled serviceman and relating specifically
to the Parker Airtek Dual Mode refrigeration system. Recharging Dryer - Refrigerant, Oil and Dryers Refer
to the dryer information tag on the front of the unit for the approximate charge needed for each unit. The
relatively large charge is needed because of the flooded-shell evaporators. Use the following to assess the
adequacy of the charge when unsure:
Because of the widely fluctuating pressures occurring when the Dual Model system unloads, it is
impractical to use pressures or sight glass indications to determine correct charge. Gross undercharge
results in a hot suction line and overheated compressor. Gross overcharge is indicated if the head and
suction pressure rises greatly when the unit is loaded. Remember to clean the condenser before deciding
on the charge.
The sight glass should stay filled most of the time when the dryer has its customary air load. It is normal
for the glass to break up when the condenser fan starts if the load is light or when the unit unloads. It may
take time to refill when it reloads. Don’t charge to clear the glass with no load; that will be too much.
All units have a charging fitting on the evaporator shell. The unit must be charged through this fitting and/or
the liquid line service valve. The best way is to dump liquid into both ports with the dryer off, then start up
and continue feeding a full stream of liquid into the evaporator until charged.
Do not charge vapor. You want the charge installed as fast as possible so the oil will be returned.
Additional oil is added at the factory to compensate for the migration with the freon. If a compressor is
replaced, remove the drain plug from the evaporator shell to drain any excess oil trapped. If that isn’t
possible, it may be necessary to remove oil from the system after start-up. Excess oil is lubricated by
noisy and vibrating compressor operation. If a replacement evaporator is installed, oil should be added.
Prolonged operation with insufficient charge or bad TXV may cause oil to be trapped in the evaporator. If
the compressor is still good, this oil will return within a few minutes of operation with the correct conditions.
For R-22 applications use 150w refrigeration mineral oil. For R-134a or R404a applications use synthetic
POE refrigeration oil.
Replace both suction and liquid filter-dryers together whenever the system has been exposed to air or
water, unless it’s brand new or you know how much air has gone through it. Solids will be caught in the
suction drier even if the system is dry.
NOTE
: 4000 scfm & up: A complaint of pressure tripping only on start-up is usually due to air through
the dryer when it is shut down or low cooling pressure rather than overcharge. This causes refrigerant to
migrate backwards from the evaporator and overfill the high side of the system.
8.1
Evaporator Leaks
If there is a leak between the tube and shell side of the evaporator, the usual symptom is high
head pressure, because the air pressure is higher than the refrigerant pressure.
To determine this, bypass airflow, stop dryer, and observe head pressure after it stabilizes. 20
minutes is sufficient. If the pressure is much higher than that corresponding to the ambient
temperature, there is air in the system. Purge air at compressor discharge or receiver inlet to
verify.
Gross leak checking of the evaporator is done at the separator drain with air pressure off and at
least an hour wait. If a leak is verified, it can often be fixed by removing the bonnets, locating the
leak with bubble soap and re-rolling the leaky tubes. Split evaporator tubes can be plugged with
special tapered brass plugs.