Hardwired Chiller Remote I/O Module Digital Inputs; Evaporator And Condenser Flow Proving (Di 1 And Di 2); Hardwired Chiller Alarms (Di 3 And Optionally Di 4); Hardwired Chiller Remote I/O Module Analog Outputs - McQuay MicroTech II Installation Manual

Hardwired Chiller Remote I/O Module Digital Inputs

Evaporator and Condenser Flow Proving (DI 1 and DI 2)

The CSM requires proof of evaporator flow. DI 1 on the remote I/O module must be wired to dry contacts, indicating
water flow through the chiller's evaporator. Since the chiller's unit controller requires flow status information through the
same evaporator, a double throw relay is used to supply separate dry contacts to both the CSM and the Chiller. This relay
can be energized using 24 VAC power from the remote I/O module. See Figure 30 for wiring detail.
Proof of condenser flow is required on water-cooled chillers. DI 2 on the remote I/O module must be wired to dry contacts
indicating water flow through the chiller's condenser. Since the chiller's unit controller requires flow status information
through the same condenser, a double throw relay must be used to supply separate dry contacts to both the CSM and the
Chiller. This relay can be energized using 24 VAC power from the remote I/O module. See Figure 30 for wiring detail.
If the chiller controls its own condenser pump or if it is air-cooled, a jumper must be placed across DI 2.

Hardwired Chiller Alarms (DI 3 and optionally DI 4)

A hardwired chiller's remote I/O module has two digital inputs (DI) available for connection to the dry contacts of the
chiller unit controller's alarm output signal. Chillers typically have one alarm output signal wired to DI 3 (see Figure 30).
Chillers with multiple compressors (e.g. the McQuay MicroTech 200 series dual compressor centrifugal chiller) may have
two alarm output signals. If a chiller has two alarm outputs, the second output is wired to DI 4. Chillers with two alarm
outputs will be considered 50% available if one of the two alarm outputs indicate a fault alarm.
It is recommended that you wire the alarm signal to a normally open contact and have the open position indicate a fault
alarm condition at the chiller. This provides a fault indication to the CSM when the chiller does not have power.
Note: The chiller alarm must be represented on dry contacts. If other control voltage is present on the alarm contacts, the
CSM hardware may not be able to distinguish between Problem and Fault alarms. If other control voltage is present, use
this voltage to control an auxiliary relay and connect dry contacts from that relay to the DI on the remote I/O module.

Hardwired Chiller Remote I/O Module Analog Outputs

Hardwired Chiller Leaving Water Temperature Setpoint Reset (AO 1)

In a system of multiple chillers, each individual chiller normally maintains its leaving evaporator water temperature at the
same setpoint—even if that setpoint is being reset. The CSM generates this System Setpoint and may also reset it based on
a number of different functions. The setpoint is sent to every hardwired chiller via an analog output (AO 1) on that
chiller's hardwire remote I/O module.
The chiller must accept chilled water temperature reset from an external signal. A 2-10 VDC (or 4-20 mA with a
converter) signal from AO 1 on the remote I/O module is wired to an analog input on the chiller unit controller. The signal
from the CSM reflects the current CSM chiller setpoint in relation to the CSM's minimum System Setpoint and maximum
System Setpoint.
Many chillers (including McQuay MicroTech controlled chillers) only accept external setpoint reset in the form of a 4-20
mA signal. The 2-10 VDC signal from the remote I/O module must be changed to 4-20 mA with a signal converter. This
converter is wired to the same power source that supplies 24 VAC to the module and is spliced into the signal wiring as
shown in Figure 30.
Table 11 shows the specifications for a voltage to current converter.
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