The AAON Two Condenser Head Pressure II Module (ASM01891) is a control device designed to monitor and manage head pressure in HVAC units with two physically separate condenser sections. It is capable of operating either as a stand-alone unit or integrated into an E-BUS control system with a VCM-X Modular E-BUS, VCM-X WSHP E-BUS, or SA E-BUS Controller.
Function Description:
The primary function of the module is to monitor up to four individual head pressure transducers. It controls two condenser fans or water valves based on these readings. Specifically, the highest reading from transducers 1 & 2 controls Condenser Signal A, while the highest reading from transducers 3 & 4 controls Condenser Signal B. In heat pump units, the module can detect when the unit is in Heat Pump Heating mode and will force the condenser signal to 100% until this mode is exited.
The module provides a pulse width modulation (PWM) signal or voltage output signal to control the condenser fans, allowing for precise speed or valve position adjustments. It can also monitor a Reverse Valve Signal, which is crucial for heat pump applications.
Important Technical Specifications:
- Power Requirement: 24 VAC power connection with an appropriate VA rating.
- Relay Outputs: Normally open, rated for 24 VAC power only, with a 1 Amp maximum load.
- Pressure Transducers: Supports 0-667 PSI sensors. Each transducer requires its own 18-gauge shielded twisted pair cable, with the drain wire serving as the "Gnd" signal.
- Analog Outputs: 0-10 VDC or 2-10 VDC for Condenser Signal A (AOUT 1) and Condenser Signal B (AOUT 2). For these outputs, an 18-gauge shielded wire is required, with the drain wire as the "Gnd" signal.
- PWM Outputs: 0-100% Duty Cycle for ECM 142 motors. Wires for PWM output do not need to be shielded and can be any 18-gauge wire.
- Binary Inputs:
- Condenser Fan A On/Off (24 VAC Wet Input)
- Reversing Valve On/Off (24 VAC Wet Input)
- Condenser Fan B On/Off (24 VAC Wet Input)
- Binary Outputs (Dry Contact Output Rated for 24 VAC):
- Condenser A Enable Relay
- Reversing Valve A Enable
- Condenser B Enable Relay
- Reversing Valve B Enable
- Operating Environment: Temperature range between -30°F and 150°F, not exceeding 90% RH levels (non-condensing).
- Dimensions: Approximately 5.71 inches in length, 5.64 inches in width, and 0.29 inches in height (excluding mounting tabs).
Usage Features:
- Stand-Alone Operation: The module can operate independently using its OPTIONS dip switch to adjust the Head Pressure setpoint. The default setpoint for an Air Cooled Condenser (R410-A refrigerant) is 340 PSI, and for a Water Cooled Condenser (R410-A refrigerant) is 235 PSI.
- E-BUS Integration: Up to two modules can be daisy-chained and connected to a VCM-X Modular E-BUS, VCM-X WSHP E-BUS, or SA E-BUS Controller. In this configuration, setpoints are received from the controller.
- Condenser Type Selection: ADDRESS Dip Switch 1 is used to designate the condenser type: ON for water-cooled, OFF for air-cooled. This affects the analog output signal type (2-10 VDC for water valve, 0-10 VDC for condenser fan). Power must be cycled after setting this switch.
- Module Addressing (Communicating Mode): ADDRESS Dip Switch 2 is used when multiple modules are present. OFF for a single module or Module 1, ON for Module 2.
- Circuit B Alarm Control: ADDRESS Dip Switch 3 allows disabling Circuit B alarms when only one condenser is used (ON to disable, OFF to enable).
- Reversing Valve Configuration: ADDRESS Dip Switch 4 sets the reversing valve operation: OFF for ON to Heat/OFF to Cool, ON for ON to Cool/OFF to Heat.
- Cooling Mode Operation: If configured for the reversing valve to be energized in Cooling Mode (Dipswitch 4 ON), the module enters Cooling Mode when condenser signal inputs are ON. Condenser Enable Relays energize, and output signals (0-10 VDC, 2-10 VDC, or 0-100% PWM) adjust to maintain the desired head pressure setpoint.
- Heating Mode Operation: If configured for the reversing valve to be energized in Heating Mode (Dipswitch 4 OFF), the module enters Heating Mode when condenser signal inputs are ON. In this mode, condenser output signals go to 100% until the mode changes.
- Safeties: Includes high pressure safety (fan to 100% if head pressure > 500 PSIG), low pressure safety (alarm if head pressure < 1 PSIG), and a 50 PSI above setpoint safety (condenser signal to 100%).
Maintenance Features:
- LED Diagnostics: The module is equipped with several LEDs for verifying operation and troubleshooting:
- PWR LED: Indicates power is supplied to the module. Should be continuously lit.
- COMM LED: Indicates communication with a VCM-X series or SA series controller. Blinks on and off when communications are detected. Should not light up in stand-alone mode.
- STAT LED: Blinks out the number of installed sensors upon power-up.
- ALARM LED: Blinks out diagnostic codes (e.g., 0 blinks for no problems, 1 for no sensors detected, 2 for high head pressure, 3 for low head pressure).
- Relay LEDs (R1, R2, R3, R4): Light up when their respective relays (Condenser A Enable, Reversing Valve A Enable, Condenser B Enable, Reversing Valve B Enable) are active.
- Troubleshooting Flowchart: A detailed flowchart is provided for troubleshooting common issues in stand-alone mode, guiding users through checks for power, LED status, sensor readings, and refrigerant charge.
- Pressure Sensor Chart: A table correlating voltage readings from pressure transducers to corresponding pressure values (PSI) is provided to aid in diagnosing transducer-related problems.
- Non-User Serviceable Parts: The module contains no user-serviceable parts. For malfunctions, qualified technical personnel should be contacted.
- Wiring Considerations: Emphasizes checking wiring lead tightness, proper shielding for transducer and analog output cables, and correct polarity for 24 VAC connections to prevent damage.
The module is designed for robust control of condenser head pressure, offering both stand-alone and integrated solutions with comprehensive diagnostic capabilities through its LED indicators and troubleshooting guidelines.
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