Sequence Of Operation - Bard W48A2PQ Installation And Service Instructions Manual

SEQUENCE OF OPERATION

WALL-MOUNT UNIT SEQUENCE OF
OPERATION
Overview
This product is designed to function like a typical
Telecom air conditioning system with an outdoor
air-cooling damper. However, the FCU system does
have some special features, like a PLC control which
allows for advanced alarming and a "DC Free Cooling"
feature that allows for forced emergency ventilated
cooling anytime "shore power" VAC power from the
utility company is lost. The internal controls within
this unit automatically recognize a loss of shore power,
energizing the indoor blower motor and powering the
actuator to open the damper to bring in outdoor air.
The power utilized during this time is the stored battery
power from the equipment shelter.
Indoor Blower
The indoor blower is an AC voltage motor. For the
blower to activate, this action must take place:
• 24VAC from terminal N07 (Blower Motor Start Relay)
Free Cooling Damper
This controller is enabled for dewpoint control,
specifically examining the combination of temperature
and relative humidity to determine the proper control
of cooling. This calculated dewpoint property then
determines the proper mode of cooling—Outdoor Air,
Mechanical Cooling, or both. To signal the 24VAC
damper actuator to open, a 2-10VDC signal must come
from the Y2 terminal.
Cooling Call
When a call for cooling generates from the controller,
the system will first determine which mode of cooling
to employ based on the outdoor temperature, the
outdoor humidity, and the indoor temperature.
• If the outdoor temperature and humidity ratio are
conducive to free cooling, the control board will
send:
1. 2-10VDC Signal from Y2 (Damper Signal)
- Modulates damper to achieve 55°F at
supply air temperature sensor
2. 24VAC from terminal N07 (Blower Motor Start
Relay)
Manual 2100-642
Page 38 of 82
• If the outdoor conditions are conducive to free
cooling, but a 2nd stage cooling call is generated,
the board will additionally add 24VAC signal
from the N02 terminal to the CCM, activating the
compressor. The damper will limit outdoor air to
keep supply air temperature at 55°F.
• If conditions outside are not conducive to free
cooling, the control board will send:
1. 24VAC signal from N02 to CCM (Compressor)
2. 24VAC from terminal N07 (Blower Motor Start
Relay)
3. 0-10VDC signal from Y1 (Speed Voltage)
Heating Call
When a call for heating generates from the controller,
the control board will send:
1. 24VAC signal from terminal N04 to heat strip
contactor 1.
2. 24VAC signal from terminal N05 to heat strip
contactor 2.
Loss of Utility Power
1. 2-10VDC Signal from terminal Y2 (Damper Signal)
- Modulates damper to achieve 55°F at supply
air temperature sensor
2. 24VAC from terminal N07 (Blower Motor Start
Relay)
Special Considerations
• High Pressure Situation – The high pressure switch
routes through the compressor control module
(CCM), which allows one switch opening followed
by a delay (soft lockout) of at least 2 minutes
before trying again. If the switch is still open—or
opens again on the same call—the CCM locks out
the compressor and outdoor fan. Additionally, the
CCM will send 24V to the high pressure alarm
relay, which will then send a digital input to the DI
3 terminal.
• Low Pressure Situation – The low pressure switch
is routed directly to DI 4 on the board and has a
very specfic scheme of operation:
1. If the switch opens, the board ignores the
switch for 2 minutes (OAT above 50°F) or 3
minutes (OAT below 50°F).
2. If the switch is still open after the delay, the
board will stop compressor and outdoor fan
function (soft lockout) for 2 minutes.