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HIGH-VOLTAGE
RELAY MODULES
DSIO2) — The DSIO modules close contacts to energize sup-
ply and condenser fan contactors. The modules also control
compressor contactors, compressor unloaders, compressor
crankcase heaters, heat interlock relay, and power exhaust
contactor. In addition, DSIO outputs provide a discrete remote
alarm light signal (all sizes) and a remote alert light signal (siz-
es 034-078). Inputs to the DSIO module are the remote occu-
pied/unoccupied signal, compressor status (through the com-
pressor lockout [CLO] relays), and high-pressure switches
(safety circuits).
KEYPAD AND DISPLAY MODULE (HSIO) — This de-
vice consists of a keypad with 6 function keys, 5 operative
keys, 12 numeric keys, and an alpha-numeric 2 line, 24 charac-
ter per line display. Key usage is explained in Keypad and Dis-
play Module section on page 9. The HSIO is a field-installed
accessory.
ECONOMIZER ACTUATOR — The PIC controls output a
4 to 20 mA signal to the optional economizer actuator in the
unit to modulate it as required by the control algorithm. Econo-
mizer dampers use a spring-return type actuator to allow auto-
matic closing of the outdoor air damper on power loss. Actua-
tor is factory-set to match factory damper rotation.
VARIABLE FREQUENCY DRIVE — If variable frequen-
cy drive (VFD) is used for supply-fan control, the PSIO1 out-
put may be used to control the VFD. Either factory-installed
optional VFD or field-supplied VFD may be used.
INLET GUIDE VANES — If the inlet guide vanes (IGV) op-
tion is used for supply fan control, the PSIO1 output is used to
control the IGV actuator.
MODULATING POWER EXHAUST — The PIC controls
output a 4 to 20 mA signal to the power exhaust damper actua-
tor in the unit to modulate the exhaust fan as required by the
control algorithm.
THERMISTORS AND REFRIGERANT PRESSURE
TRANSDUCERS — The unit control system gathers infor-
mation from the sensors to control the operation of the unit.
The units use 5 standard and 2 additional accessory ther-
mistors and up to 4 accessory pressure transducers to moni-
tor various temperatures and pressures at selected points
throughout the system. See Table 1.
FAN STATUS PRESSURE SWITCH — The
Switch (FSS) is a snap-acting SPDT switch. The switch senses
Table 1 — Thermistors and Unit Operation Control Pressure Transducers
SENSOR
Compressor A located at the discharge service valve — Senses discharge pressure (replaces T3)
DPT1*
Compressor A located at the LPS connection on the compressor instead of LPS1 (low-pressure switch)
SPT1*
— Senses suction pressure
Compressor B located at the discharge service valve — Senses discharge pressure (replaces T-4)
DPT2*
Compressor B located at the LPS connection on compressor instead of LPS2 — Senses suction
SPT2*
pressure
Located in supply-air section — Senses supply-air temperature (SAT)
T1
Located in return air section, right hand side — Senses return-air temperature (RAT)
T2
Located in condenser coil circuit no. 1 at the return bend end (034-048 units); or at the header end
T3
(054-104 units) — Senses saturated condensing temperature (SCT1)
Located in condenser coil circuit no. 2 at the return bend end (034-048 units); or at the header end
T4
(054-104 units) — Senses saturated condensing temperature (SCT2)
Coiled at the corner post (034-048) or below main control box (054-104) — Senses outdoor-air temper-
T5
ature (OAT)
Located in compressor A suction service valve — Senses suction gas temperature (SGT1)
T6
Located in compressor B suction service valve — Senses suction gas temperature (SGT2)
T7
*Accessory sensors (all sizes), which are also available as factory-installed option
with optional Control Options Module package (sizes 034-074 only).
†Unit sizes 034-048.
**Unit sizes 054-104.
(DSIO1 and
the airflow supplied by the unit supply fan and provides the
PSIO1 module with a 10-vdc discrete signal for fan status.
CHECK FILTER PRESSURE SWITCH — The Check Fil-
ter Switch (CFS) is a snap-acting SPDT switch. When dirty fil-
ter elements cause the pressure drop across the filter section to
exceed the switch setting, the switch contacts close and send a
discrete signal (5 vdc) to the PSIO1 module.
Optional and Accessory Control Components
SPACE TEMPERATURE SENSOR (T-55) — The T-55
Space Temperature Sensor (STS) is shipped inside the unit in
the main control box. The sensor is installed on a building inte-
rior wall to measure room air temperature. The T-55 also in-
cludes an override button on the front cover, to permit occu-
pants to override the Unoccupied Schedule (if programmed).
See Fig. 3.
SPACE TEMPERATURE SENSOR (T-56) (Use with CV
Only) — The T-56 Space Temperature Sensor (a field-
installed accessory) may be used on CV installations. This sen-
sor includes a sliding scale on the front cover that permits an
occupant to adjust the space temperature set point remotely.
See Fig. 4.
RELATIVE HUMIDITY (RH) SENSORS — The accesso-
ry field-installed RH sensors measure relative humidity of the
air within the occupied space, in the return-air ductwork and/or
in the outdoor air hood. The RH sensors provide input signals
to the PSIO2 (control options) module. There are two types of
RH sensors available, wall-mounted or duct-mounted. Humidi-
ty sensors require separate and isolated 24-vac power
source(s). See Fig. 5.
NOTE: Sizes 034-074 also require the installation of the
control options module (PSIO2), available as a factory-
installed option or field-installed accessory.
INDOOR AIR QUALITY (CO
Air Quality sensor accessories monitor carbon dioxide levels.
This information is used to modify the position of outdoor air
dampers to admit more or less outdoor air to dilute indoor CO
levels. Two types of sensors are available. The wall sensor can
be used to monitor conditions in the conditioned air space. The
duct sensor monitors conditions in the return air duct. Both
wall and duct sensors use infrared technology. The wall sensor
is available with or without an LCD readout to show CO
Fan
Status
els in ppm. See Fig. 6.
LOCATION AND FUNCTION
Thermistors
6
) SENSORS — The Indoor
2
lev-
2
PART NO.
HK05ZG002
HH79NZ014†
HH79NZ026**
HH79NZ013
HH79NZ014†
HH79NZ026**
HH79NZ026
2
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Troubleshooting
