Manual 2100-484E
Page 8 of 22

SEQUENCE OF OPERATION – COOLING AIR

CONDITIONERS – (NO ECONOMIZER)

First stage cooling set point is the setting (SP) input into the
controller. Factory default is 75F/24C. At Stage 1 cooling
SP, the blower of the lead unit will come on (if not already
operating because of continuous fan selection for lead unit).
The DC fan will also operate at this time if controller is
configured for free cooling using DC fan, and if outdoor
temperature is 1F or more below (dFon) setting for DC fan
operation 50, 55 or 60F (default is 55). DC fan is off at 1F
above the (dFon) setting.
At Stage 2 cooling call (SP + 2F), the compressor for lead
unit comes on.
At Stage 3 cooling call (SP + 4F), the blower for the lag unit
comes on, followed 10 seconds later by the compressor for
the lag unit.

SEQUENCE OF OPERATION – COOLING AIR

CONDITIONERS – (WITH ECONOMIZERS)

Note: Economizer Logic Enabled must be switched from
No to Yes in the Programming Menu.
First stage cooling set point is the setting (SP) input into the
controller. Factory default is 75F/24C. On a call for 1st Stage
cooling, the blower will come on immediately (if not already
on - See Blower Operation), and the Stage 1 LED will blink for
10 seconds before going solid, at which time the cooling output
turns on. If the outdoor temperature and humidity conditions
are below the set point of the economizer enthalpy control, the
economizer will operate instead of the compressor. If outdoor
conditions are not acceptable for free cooling, the compressor
will automatically operate instead of the economizer.
Stage 2 cooling is 2F (1C) warmer than Stage 1. On a call for
2nd Stage cooling, the blower of the lag unit is turned on, and
the Stage LED will blink for 10 seconds before going solid, at
which time either the economizer or the compressor will turn
on - based on enthalpy control setting and outdoor conditions.
Stage 3 cooling is 2F (1C) warmer than Stage 2. On a call for
Stage 3 cooling, a signal is input into the lead unit
economizer to cancel economizer and force lead unit
compressor on. Stage 3 LED comes on solid with no
blinking.
Stage 4 cooling is 2F (1C) warmer than Stage 3. If the lead unit
compressor and lag unit economizer cooling capacity are not
sufficient to hold the building temperature, and Stage 4 calls for
cooling, a signal is input into the lag unit economizer to cancel
economizer and force the lag unit compressor on. Stage 4 LED
comes on solid with no blinking.
When any of the four (4) Stages are satisfied, the stage LED
will blink for 10 seconds before the stage is actually turned
off.
DC3003 only: Stage 5 cooling is 1F warmer than Stage 4.
Stage 5 LED is located on the alarm board mounted inside the
controller, and is marked Y1. There is also a Y2 LED, and
Y1 and Y2 will cycle together.
Humidity controller set point should be in 55-60%
relative humidity area: Setting controller to lower
settings will result in excessive operating time and
operating costs for the electric reheat, and in
extreme cases could cause evaporator (indoor) coil
freeze-up if there are periods of light internal
equipment (heat) loading.
CAUTION

HUMIDITY CONTROL OPTION

Note: This function is not available if controller is
configured for heat pump.
The standard air conditioning system can be adapted to
perform dehumidification control by addition of a
simple humidity controller that closes-on-rise, and is
connected to terminals H1 and H2 on the main controller
board. Recommended Bard part number is 8403-038
(H600A 1014). See appropriate connection diagram -
Figures 1, 2 or 3 for this connection.
The humidity control logic needs to be enabled in the
program menu. Go to HuLE in the Programming Menu
and change from No to Yes. This permits the following
sequence of operation:
1.Temperature control always has priority over
dehumidification. If there is any stage of cooling
demand active, the dehumidification sequence is
locked out.
2.If all stages of cooling are satisfied, and relative
humidity is above the set point of humidity
controller:
a.The green “Dehumid. Operation” light will come
on, and the lag unit compressor and blower will
operate until the set point of humidity controller
is satisfied (or cancelled by a call for cooling).
b.If the space temperature drops to 67F, the electric
heater of the lead unit will cycle to help maintain
building temperature. It will cycle off at 69F.
c.If space temperature drops to 64F, the Stage 2
Heating light will come on and the lag unit
compressor operating for dehumidification mode
will cycle off until the building temperature rises
above 65F from 1st stage heat and building load.
The green “Dehumid. Operation” light stays on
during this sequence, and when Stage 2 Heating
light is Off, the compressor is On. The electric
heater in lag unit is locked out in
dehumidification mode.