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Installation
fault, or locked out on a system fault. Field connec-
tions are at CTB2 terminals 29 to 30 (system 1), and
terminals 31 to 32 (system 2). Refer to 6 and unit wir-
ing diagram.
PWM INPUT
The PWM input allows reset of the discharge air tem-
perature setpoint (when unit is programmed for Dis-
charge Air Temperature Control mode) by supplying a
"timed" contact closure. Field wiring should be con-
nected to CTB1 - terminals 13 to 20. A detailed expla-
nation is provided in the Unit Control section. Refer to
Figure 5 and unit wiring diagram.
Load Limit Input
Load limiting is a feature that prevents the unit from
loading beyond a desired value. The unit can be "load
limited" either 33%, 50%, or 66%, depending on the
number of compressors on the unit. The field connec-
tions are wired to CTB1- terminals 13 to 21, and work
in conjunction with the PWM inputs. A detailed expla-
nation is provided in the Unit Control section. Refer to
Figure 5 and unit wiring diagram.
When using the Load Limit feature,
the PWM feature will not function -
SIMULTANEOUS OPERATION OF
LOAD LIMITING AND TEMPERA-
TURE RESET (PWM INPUT) CAN-
NOT BE DONE.
REFRIGERANT PIPING
General
When the unit has been located in its final position, the
unit piping may be connected. Normal installation pre-
cautions should be observed in order to receive maxi-
mum operating efficiencies. System piping should con-
form to ASHRAE guidelines. All piping design and
installation is the responsibility of the user.
YORK ASSUMES NO WARRANTY RESPONSIBIL-
ITY FOR SYSTEM OPERATION OR FAILURES
DUE TO IMPROPER PIPING OR PIPING DESIGN.
Filter driers and sight glasses are shipped loose for field
installation on each refrigerant circuit. Field refriger-
ant piping can be connected to the condensing unit with-
out loss of the holding charge in the unit.
12
All expansion valves, liquid line solenoid valves, and
refrigerant piping are field supplied and installed.
Table 4 lists refrigerant line connections sizes per unit
model number.
REFRIGERANT LINE SIZING
Refrigerant piping systems must be designed to pro-
vide practical line sizes without excessive pressure
drops, prevent compressor oil from being "trapped" in
the refrigerant piping, and ensure proper flow of liquid
refrigerant to the thermal expansion valve. Consider-
ations should be give to:
1. Suction line pressure drop due to refrigerant flow.
2. Suction line refrigerant velocity for oil return.
3. Liquid line pressure drop due to refrigerant flow.
4. Liquid line pressure drop (or gain) due to vertical
rise of the liquid line.
Table 5 & 6 provides the pressure drops for given pipe
sizes for both liquid and suction lines. The pressure
drops given are per 100 ft. (30.5 m) of refrigerant pip-
ing. These friction losses do not include any allow-
ances for strainer, filter drier, solenoid valve, isolation
valve, or fittings.
Nominal pressure drop for solenoids, sight glass, and
driers are shown in Table 2.
Table 1 includes approximate equivalent lengths for
copper fittings.
To ensure a solid column of liquid refrigerant to the
expansion valve, the total liquid line pressure drop
should never exceed 40 psi (276 kPa). Refrigerant va-
por in the liquid line will measurably reduce valve ca-
pacity and poor system performance can be expected.
To allow adequate oil return to the compressor, suction
risers should be sized for a minimum of 1000 FPM (5.08
m/s) while the system is operating at minimum capac-
ity to ensure oil return up the suction riser. Refer to
Table 5 & 6 under column labeled "Nominal Tons (kW)
Unloaded.
Evaporator Below Condensing Unit
On a system where the evaporator is located below the
condensing unit, the suction line must be sized for both
pressure drop and oil return. In some cases a double
suction riser must be installed to ensure reliable oil re-
turn at reduced loads. Table 5 & 6 indicates when a double
YORK INTERNATIONAL
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