Carrier 38BA - Manual (Page 12)

REFRIGERANT PIPING
Use of liquid line solenoid valves
38BA008,009; 38AD012 — 0 1 6 single evaporator
coil applications; liquid line solenoid valves not
required.
38AD012 — 016 dual coil applications; single
liquid line solenoid required to deactivate upper
second-stage coil.
38AD024 — 034 liquid line solenoid valves re­
quired for each evaporator coil stage.
38AE044 — 064 may require liquid line solenoid
valves in 2 types of applications. In installations
requiring 125 ft or more of interconnecting piping,
solenoid valves are required on all coil splits to be
operated by the solenoid drop relay that is
installed in the unit. In installations where the
compressors are able to unload to a very low per­
centage of full load, it is usually necessary to install
liquid line solenoid valves on one or more of the
coil splits to assure sufficient refrigerant velocity in
the coil to return oil to the compressor.
The 38AD024 — 034 units are wired for single
pumpout control. Field-supplied liquid line sole­
noid valve(s) is required to restrict the flow of
refrigerant to the evaporator during the off cycle.
When the thermostat is satisfied, the liquid line
solenoid valve(s) will close. The unit, however, will
continue to run, evacuating the low side, until the
low pressurestat opens.
The 38BA008,009, 3 8 A D 0 1 2 0 1 6 , and
38AE044 — 064 do not require single pumpout
control or a liquid line solenoid drop when the unit
is de-energized unless the interconnecting piping
exceeds 100 ft (125 ft in the Model 38AE).
Field-supplied liquid line solenoid valves are
required on multi-evaporator coils to deactivate
upper portion of evaporator coil surface in order to
unload compressor (suction-activated unloaders) at
part-load conditions and provide single pumpout
control when last solenoid drops. Pum pdown
control is not recom m ended.
Solenoid drop protection (liquid line solenoid
valve closes, compressor shuts off and crankcase
heaters energize simultaneously) is recommended
for Series 10 cooler applications. Single pumpout is
not recommended for Series 10 cooler applications
because of possible damage due to frost pinching
of cooler tubes.
Oil return — Condensing units with multi-step
unloading m ay require double suction risers to
assure proper oil return at minimum load operating
conditions. Reduction of evaporator coil surface
should be analyzed to provide sufficient refrigerant
velocity to return oil to the compressor. Liquid
line solenoid valves may be used in certain situ­
ations to accomplish this. Bypass hot gas, if used,
should be introduced before the evaporator.
Consult Carrier System Design Manual.
Insulation — Refrigerant suction piping should be
insulated in accordance with guidelines set forth in
the Carrier System Design Manual.
Additional consideration should be given to
insulating the liquid line to prevent sweating when
low-temperature operation is expected. Since
refrigerant flashes and migrates to the outdoor coil
during off cycle due to lower outdoor coil pressure
(resulting from low outdoor temperature), the
refrigerant temperature in the liquid line may drop
below the indoor air dew point.