McQuay ACZ 045A, Installation, Operation And Maintenance Manual

Page: 49 / 104

IOMM ACZ/AGZ-1 49
Digital Inputs
Note: All Digital Inputs are 24Vac supplied by transformer T2 in the control panel. Do not use
inputs from another power supply external to the unit. This can cause failure of the Global
UNT controller.
Table 18, Digital Inputs
Input Description Location Closed Open
BI-1 Time Clock
Field Installed to TB-7 #140 &
#141
Run Stop
BI-2
Auto / Pumpdown and Stop Switch
Circuit #1
Control Panel Run
Pumpdown
Stop
BI-3
Auto / Pumpdown and Stop Switch
Circuit #2
Control Panel Run
Pumpdown
Stop
BI-4 Chilled Water Flow Switch
Field Installed to TB-7 #142 &
#143
Run Stop
Relay Outputs
All of the relay outputs are controlled by the Global UNT controller. The relays are double pole
double throw relays with contacts rated for 120Vac - 7.0 amp and a 24Vac holding coil. Refer to the
unit staging schematic.
Table 19, Relay Board Outputs
Relay Output
Number
Output
Description
1 Circuit #1 Liquid Line Solenoid Valve
2 Circuit #2 Liquid Line Solenoid Valve
3 Compressor #3 Contactor M3
4 Compressor #4 Contactor M4
5 Spare
6 Spare
7 Low Pressure Relay Circuit #1
8 Low Pressure Relay Circuit #2
Reset Options
The Global UNT controller is capable of one reset option. The reset option should be selected at the
time of purchase. Outside Air is the standard option and a Zone Terminal is necessary to activate this
option or any other reset option. Other reset options, such as chilled water, are available and requires
a software download. Field modifications can be accomplished with the Global UNT Interface Kit Part
Number 0074642001; consisting of cable supply, cable pro, and connector board.
Outside Air Reset
When selected, a Outdoor Air Temperature (OAT) sensor is connected to TB-7 terminals #134 and
#135. Four variables are used to setup the reset ramp that calculates the Actual Leaving Water
Setpoint. These are: Leaving Water Setpoint (AI-4), Reset Band selected with a Zone Terminal,
Outdoor Air High Limit (OAHL), and Outdoor Air Reset Band (OARB).
Figure 23, Outside Air Reset
LWR B
LWSP
OALL OA HL
OA R B
(OALL=OAHL - OARB)