Carrier 38AUM Series Installation, Operation & Maintenance Manual page 13

Fig: - Location of Sight Glass(es) and Filter Driers Typical 38AUMD Systems
Install Liquid Line Solenoid Valve
It is recommended that a solenoid valve be placed in the main liquid line (see Figs: - Location of Sight Glass(es) and
Filter Driers Typical 38AUMZ/D Systems) between the condensing unit and the evaporator coil. Locate the solenoid
valve at the outlet end of the liquid line, near the evaporator coil connections, with flow direction arrow pointed at the
evaporator coil. (A liquid line solenoid valve is required when the liquid line length exceeds 23m [75ft].) This valve
prevents refrigerant migration (which causes oil dilution) to the compressor during the off cycle, at low outdoor
ambient temperatures.
Solenoid drop control wiring: control the power to the liquid line solenoid through a Solenoid Valve Relay (SVR)
in all units. Use part number HN61PC005 (field--supplied, installed). 38AUMZ unit requires one SVR; 38AUMD unit
requires two relays. 38AUMD units also require a separate control power transformer for the liquid solenoid valve
loads. Use transformer part number HT01BD602, according to unit power supply.
Mount the SVR (and transformer TRAN3 when used) in unit control box. Connect per wiring schematic label on unit or
per Typical Wiring Schematic.
Capacity Control Liquid Line Solenoid Valve: Evaporator capacity staging control via direct thermostat control of a
liquid solenoid valve on the evaporator's second stage circuit is not possible with 38AU models. If this installation is a
retrofit for a unit that included automatic pressure-operated unloading, check the existing thermostat and liquid
solenoid valve wiring for possible direct thermostat control of a solenoid valve; re-wire per Fig: - Typical Piping
Connection Assembly.
Selecting an Accumulator – Because all 38AUM models use scroll compressors, an accumulator is not required. If
an accumulator is to be added, check the accumulator manufacturer's literature carefully for indication of its suitability
for use with R--410A; look for minimum working pressure of 1380 kPa (200 psig). Select the accumulator first on the
basis of its cataloged minimum capacity (tons) to ensure oil return from the accumulator, then on tube size or holding
capacity.
Make Piping Connections — Piping connections at the 38AUM unit are ball valves with stub tube extensions. Do not
open the unit service valves until all interconnecting tube brazing has been completed. The stub tube connections
include 1/4-in SAE service fittings with Schrader valve cores (see Fig: - Typical Piping Connection Assembly). Before
making any brazed connections to the unit service valves, remove both Schrader valve caps and cores and save for
re-installation. Connect a source for nitrogen to one of these service fittings during tube brazing to prevent the
formation of copper oxides inside the tubes at brazed joints.
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