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Two Condenser Head Pressure II Module Technical Guide
10
SEQUENCE OF OPERATION
VCM-X Input Commands and Modes of Operation
Input Commands (VCM-X Connection)
Condenser A & B On/Off
Instead of a hard wired input signal to the Condenser Enable
input, the VCM-X Modular Controller, VCM-X WSHP
Controller, or SA Controller communicates to the Module via
E-BUS communications. This signal indicates the compressor(s)
are called to run and drives the condenser A & B On/Off function.
Reversing Valve Enable A & B On/Off
As with the Condenser Signal On/Off function, the VCM-X
Modular Controller, VCM-X WSHP Controller, or SA Controller
communicates to the Module via E-BUS communications and
signals that the reversing valve has been energized and that
heating has been enabled.
NOTE:
When the term “ON” is used, it means there is
either 24 VAC on the appropriate Binary Input
or a call-to-run signal is being received from a
VCM-X series or SA series controller. When the
term “OFF” is used, it means there is either 0
VAC on the appropriate Binary Input or the call-
to-run signal from a VCM-X series or SA series
controller has been removed.
Sensor Reading Routine
The Two Condenser Head Pressure Module is used on units
with two physically separate condenser sections. Up to (2) Head
Pressure Sensors can be monitored in each section. The highest
of the two readings in each section will be used to control the
condenser fan(s) in that section.
Air from the condenser fan(s) in each section flows through both
condenser coils. As a result, if you modulate the fan(s) based on
the highest reading, you will have enough air flow for both coils.
The highest reading of Head Pressure Sensors 1 & 2 controls
Condenser Fan A. The highest reading of Head Pressure Sensors
3 & 4 controls Condenser Fan B.
Modes of Operation
OFF Mode
The Head Pressure Control Board is in the OFF Mode when the
Condenser Input Signals are “OFF.” In this mode, all relays are
off, the Analog Output is 0 VDC, and the PWM Output is 0%
Duty Cycle.
Cooling Mode
If the Head Pressure Controller has been configured for the
Reversing Valve to be energized in the Cooling Mode and to Fail
to the Heat Mode (Dipswitch 4 is set ON), then the Head Pressure
Controller will be in the Cooling Mode when one or both of the
Condenser Signal inputs is “ON” and the Reversing Valve Enable
Signal is “ON”. In this circumstance, the Reversing Valve Enable
Relay Output(s) will energize for indication purposes.
If the Head Pressure Controller has been configured for the
Reversing Valve to be energized in the Heating Mode and to
Fail to the Cool Mode (Dipswitch 4 is set OFF), then the Head
Pressure Controller will be in the Cooling Mode when one or
both of the Condenser Signal inputs is “ON” and the Reversing
Valve Enable Signal is “OFF”.
The Condenser Enable Relays will energize to enable the
Condenser Fans or Water Valves. In a water system, the Water
Flow Valve will start at 75% for 3 minutes. The Condenser Output
Signals will then automatically adjust between 0 and 100% to
maintain the desired Head Pressure Setpoint. The Condenser
Output Signals can be a 0-10 VDC, 2-10 VDC or 0-100% PWM
signal provided by the appropriate output. Both outputs mirror
each other.
Heating Mode
If the Head Pressure Controller has been configured for the
Reversing Valve to be energized in the Cooling Mode and to
Fail to the Heat Mode (Dipswitch 4 is set ON), then the Head
Pressure Controller will be in the Heating Mode when one or
both of the Condenser Signal inputs is “ON” and the Reversing
Valve Enable Signal is “OFF”.
If the Head Pressure Controller has been configured for the
Reversing Valve to be energized in the Heating Mode and to
Fail to the Cool Mode (Dipswitch 4 is set OFF), then the Head
Pressure Controller will be in the Cooling Mode when one or both
of the Condenser Signal inputs is “ON” and the Reversing Valve
Enable Signal is “ON”. In this circumstance, the Reversing Valve
Enable Relay Output(s) will energize for indication purposes.
In this mode, the Condenser Output Signals will go to 100% and
remain there until it leaves the Heating Mode.
NOTE:
The Reversing Valve Dipswitch 4 setting
determines whether the Reversing Valve Dipswitch
4 Relay is ON to Heat / OFF to Cool or ON to
Cool / OFF to Heat.
NOTE:
The Reversing Valve Enable outputs are for
indication only and are not wired to anything.