10
4.0 INSTALLATION
4.3.3 Elevating Unit
WARNING:
Secure an elevated unit and
its elevating stand in order to prevent tipping. Failure to
do so may result in severe personal injury or death.
If elevating the unit, either on a flat roof or on a slab,
observe the following guidelines.
If elevating a unit on a flat roof, use 4” x 4”
[10.2 cm x 10.2 cm] or equivalent stringers positioned
to distribute unit weight evenly and prevent noise and
vibration.
Location
NOTICE:
DO NOT
block drain openings
on bottom of unit.
If unit must be elevated, secure unit and elevating
stand such that unit and/or stand will not tip over
or fall off. Keep in mind that someone may try to
climb on unit.
DO NOT BLOCK
OPENINGS
IN BASE PAN
BASE PAD
(CONCRETE OR OTHER SUITABLE
MATERIAL)
ST-A1226-03-00
4.4 Refrigerant Line Set Selection
4.4.1 Replacing Existing
Systems
To prevent failure of a new unit, the existing line set
must be correctly sized for the new unit and must
be cleaned or replaced. Care must be taken so
the expansion device is not plugged. For new and
replacement units, a liquid line filter drier must be
installed and the line set must be properly sized.
Test the oil for acid. If it tests positive for acid, a
suction line filter drier is mandatory.
IMPORTANT:
When replacing an
R-22 unit with an R-410A unit, either replace
the line set or ensure that residual mineral oil is
drained from existing lines including oil trapped in
low spots
4.4.2 Line Set Application
Considerations
The following are special considerations that need
to be addressed when selecting and installing a
line set.
•
Additional refrigerant charge
•
Fitting losses and maximum equivalent length
considerations
•
Refrigerant migration during the off cycle
•
Oil return to the compressor
•
Capacity losses
•
System oil level adjustment
4.4.2.1 Oil Return to Compressor
Small amounts of compressor crankcase oil is
picked up and carried out of the compressor by
the moving refrigerant and is circulated through the
system along with the refrigerant before it returns
to the compressor crankcase. It is critical to the
life of the compressor for the oil to be able to
return to the compressor to maintain an adequate
level of oil in the compressor crankcase. Oversized
suction lines result in inadequate refrigerant velocities
to carry the oil along with the refrigerant and
will cause the oil to accumulate in the low spots
in the suction line instead of being returned to the
compressor crankcase. This is especially true for
long line lengths. Variable speed systems present
an additional challenge due to the fact that the system
operates at a significantly reduced refrigerant
flow rate for a significant percentage of operating
time. Only use the suction line sizes listed in Table 2
to assure proper oil return.
DO NOT
oversize suction
line!
4.4.2.2 Refrigerant Migration
During Off Cycle
Long line set applications can require a consider-
able amount of additional refrigerant. This additional
refrigerant needs to be managed throughout the
entire ambient operating envelope that the system
will go through during its life cycle. Off-Cycle
migration is where excess refrigerant condenses
and migrates to the coldest and/or lowest part of
the system. Excessive build-up of refrigerant at the
compressor will result in poor reliability and noisy
operation during startup. Section 4.5.2 demonstrates
the required unit configuration for different
applications.
The outdoor unit controls can energize a portion of the
compressor motor stator during the off cycle as needed
to prevent liquid refrigerant from accumulating inside the
compressor, similar to how a crankcase heater functions
on a conventional system.
