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ZB
Series
Application Guide
Brief Power Interruptions
Brief power interruptions (less than ½ second) may result in powered
reverse rotation of single-phase refrigeration scroll compressors.
High-pressure discharge gas expands backward through the scrolls at
power interruption causing the scroll to orbit in the reverse direction. If
power is reapplied while this reversal is occurring, the compressor may
continue to run noisily in the reverse direction for several minutes until
the compressor internal protector trips. This has no negative effect on
durability. When the protector resets, the compressor will start and
run normally.
No time delay is required on three phase models to prevent reverse
rotation due to power interruptions.
3.3 Oil Types
In HCFC R-22 applications, mineral oil is used in the compressor. Polyol
ester lubricants must be used with HFC refrigerants (R404A, R507 and
134a).Compressors using polyol ester oil are identified with an "E" in
the model number. A separate form may be requested (Form 93-11)
which lists Emerson approved lubricants that may be used to recharge
these compressors or if the addition of oil is required. See compressor
nameplate for original oil charge. A complete recharge should be four
ounces (118 ml) less than the original oil charge. If the oil level is above
the sight glass, it may lead to oil circulation rates higher than 1.5% which
may lead to decreased capacity as the oil coats the evaporator coils.
3.4 Deep Vacuum Operation
WARNING: DO NOT RUN A REFRIGERATION SCROLL COMPRESSOR IN A
VACUUM. FAILURE TO HEED THIS ADVICE CAN RESULT IN PERMANENT
DAMAGE TO THE COMPRESSOR.
A low-pressure control is required for protection against vacuum
operation. See the section on pressure controls for the proper set
points. (See Table 1)
Scrolls compressors (as with any refrigeration compressor) should never
be used to evacuate refrigeration or air conditioning systems.
The scroll compressor can be used to pump-down refrigerant in a unit
as long as the pressures remain within the operating envelope. Low
suction pressures will result in overheating of the scrolls and permanent
damage to the compressor drive bearing or cause the scroll temperature
protection to activate.
3.5 Shell Temperature
Certain types of system failures, such as condenser or evaporator fan
blockage or loss of charge, may cause the top shell and discharge line to
briefly but repeatedly reach temperatures above 350°F (177°C) as the
compressor cycles on its internal protection devices. Care must be taken
to ensure that wiring or other materials, which could be damaged by these
temperatures, do not come in contact with these potentially hot areas.
3.6 Suction and Discharge Fittings
Scroll compressors are available with stub tube or Rotalock connections.
The stub tube version has copper plated steel suction and discharge
fittings. These fittings are far more rugged than copper fittings used on
other compressors. Due to the different thermal properties of steel
and copper, brazing procedures may have to be changed from those
commonly used. Assembly and brazing procedures are explained in
the later part of application guide.
3.7 Starting Characteristics Of Single-Phase Compressors
Single-phase scroll compressors are designed with PSC type motors and
therefore will start without the need of start assist devices in most
applications. However, if low voltage conditions exist at start up, protector
trips can result. Therefore, start assist devices (start capacitors and relays)
are available to maximize starting characteristics under abnormal
conditions.
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