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AE4-1395 R5
Compressor Selection & Change-Out
The replacement digital scroll compressor should be
compared to the non-modulating compressor in at least
these three areas:
1. Performance – the full load capacity of the digital
scroll should be approximately equal to the capacity
of the compressor being replaced. In some cases
in might make sense to 'right size' the compressor
capacity for the load if the compressor is grossly
oversized.
2. Electrical – the digital scroll compressor RLA and
LRA should be compared to the compressor being
replaced. Contactor, wire, breaker/fuse, and run
capacitor sizes should be evaluated.
3. Mechanical – in most cases the compressor
mounting will be identical for the non-modulating
and the digital scroll. There could be minor
differences in the suction and discharge tubing
locations, as well as the height of the compressor.
The following steps should be followed to remove the
non-modulating compressor from the system.
1. Using an EPA approved refrigerant recovery
machine, recover the system refrigerant charge
from the low and high sides of the system.
2. Disconnect and lockout the power supply.
Confirm that all voltage sources have been
disconnected by using a voltmeter. Disconnect the
conduits and wiring to the compressor and move
them out of the way as much as possible.
3. By using manifold gauges, verify that the system
refrigerant charge is completely recovered from
the system. Suction and discharge pressures must
be 0 psig.
4. Using a tubing cutter, cut the suction and discharge
lines close to the compressor.
5. Remove the compressor mounting bolts.
6. Plug the compressor suction and discharge
connections to prevent the spillage of oil from the
compressor when removing it from the system.
7. Using the appropriate lifting devices, carefully
remove the compressor from the system.
The following steps should be followed to install the digital
compressor into the system.
1. Before removing the rubber plugs, install the
compressor in the unit on the mounting grommets
using the appropriate lifting devices.
2. Install the compressor mounting bolts.
3. Connect the suction and discharge lines using
standard brazing practices.
4. If the compressor has an external modulation valve
and tubing (ZPD34-ZPD54K5, ZPD61-ZPD83KC,
ZPD91KC, ZPD104KCE, ZPD122KCE, and
ZRD36-81KC only) refer to
Figure 6
for the correct
valve orientation and position. Wrap a wet rag
around the valve and complete the assembly by
brazing the valve and tubing into place.
5. Check for leaks using nitrogen with a properly sized
regulating and relief valve.
6. Connect conduits and wiring to the compressor.
Inspect and/or replace the contactor. If the
compressor is 1-phase, install the correct run
capacitor.
NOTICE
The above procedures for changing the
compressor are not comprehensive and additional
steps/procedures may be necessary.
Refrigerant Flow Control
In the system with a digital compressor, the refrigerant
flow control valve is required to control flow across a wide
range of flow rates and varying pressure differentials.
Most balanced port thermostatic expansion valves can
control flow down to about 40% of their rated capacity.
Excessive hunting and loss of superheat control can
result when asking a thermostatic expansion valve to
operate outside of its design range. For this reason,
the expansion device needs to be evaluated to ensure
reliable operation over the expected operating range.
Limiting the minimum compressor modulation rate to
a value that the expansion valve can tolerate should
be considered. Electronic expansion valves should be
considered if modulation over the entire range of the
compressor’s modulation range is anticipated.
Evaporator Air Flow
For the highest level of energy savings, comfort, and
efficiency the variable capacity system should be capable
of varying the air flow. Variable frequency drives and
tapped blowers are two means of reducing air flow.
Reducing air flow in humid or maritime climates is
important to maintain coil temperatures low enough to
