Overview
This document is a supplement to the Microprocessor Controller for Dedicated Outdoor Air System Installation, Operation and Maintenance Manual (IOM). All safety information from the IOM also pertains to Heat-Cool Only controls.
Heat-Cool Only Overview
The Heat-Cool Only system is designed to enable third-party control of a packaged DX or Heat Pump unit while preserving the safeties of the refrigeration and heating systems. The Heat-Cool Only controller is factory installed and commissioned, managing the unit's refrigeration and heating components. Refrigeration system safety is maintained through monitoring pressures and temperatures within the circuit. The third party is responsible for controlling:
- Supply and exhaust airflow
- Cooling or heating operation selection
- Dehumidification enable
- Temperature setpoints
- Emergency shutdown
A field-supplied and installed third-party device provides occupancy, temperature, and airflow monitoring. This device interfaces with the Heat-Cool Only controller via a terminal strip in the control cabinet.
END DEVICES: End devices for Heat-Cool Only operation are factory-provided for the heat/cooling control system. Sensors for third-party controller operation must be provided and installed by the third party. Additional end devices not provided by the factory may be used by the third-party control system. Refer to unit submittal information for specific unit configuration and factory-provided end devices.
WARNING: Powering the third-party controller is the third party's responsibility. A transformer supplied and installed by the third party must power their controller. This power cannot be sourced from the control panel. The third-party device must not be mounted within the unit's electrical control panel.
System Diagram: A block diagram illustrates the system architecture. It shows a "Third Party Controller" communicating via a "Terminal Strip" with the "Heat-Cool Only Controller". The "Heat-Cool Only Controller" manages "Refrigeration & Heating Components" and "Non-tempering Components". Arrows indicate bidirectional communication between the controller and the terminal strip, and between the terminal strip and the Heat-Cool Only Controller.
Third Party Responsibilities
Occupancy, temperature, airflow, and third-party device power for Heat-Cool Only systems are the responsibility of the third party via a dedicated device. This includes timing of occupied modes and logic for enabling/modulating all non-refrigeration or heating components.
Occupancy
Scheduling and occupancy mode control are the responsibility of the third party.
Airflow
Maintaining proper airflow by enabling and modulating fans and dampers is the responsibility of the third-party controller. During normal operation, airflow should continue over the unit's heat exchangers after the remote start command to the Heat-Cool Only controller is removed. For units with variable speed compressors, compressors may take up to two minutes to stop completely. In heating mode, supply airflow should continue until supply air temperatures drop below 80°F to dissipate residual heat and prevent excessive component temperatures.
Damper Positioning
Dampers require power and a position signal for modulation. Before starting fans, the third party must ensure an open airflow path by confirming the damper end switch is closed (if installed).
Fan Modulation
The third-party controller is responsible for enable and modulation signals.
- Supply Fan: Supply fan modulation must follow specific guidelines. The end switch signal must be received before starting any fans.
- Cooling or Heat Pump Heating: Fan turndown must be limited to a minimum of 50% of designed airflow to allow adequate refrigeration system modulation. Modulating below 50% may lead to loss of space temperature control and negatively impact components.
- Electric Heat: Supply fan modulation must meet the minimum airflow requirements of the electric heater manufacturer. Generally, 500 FPM is adequate for most applications. Contact technical support for specific product information.
WARNING: When modulating gas furnace heating capacity, maintain a maximum temperature rise and minimum airflow to prevent improper combustion and unit damage. Refer to Appendix B for specific minimum airflow requirements.
Gas Furnace Heat: Limit turndown to the minimum airflow based on unit size or 50.0% of design airflow, whichever is greater. Refer to unit submittal information for exact gas furnace performance data.
- Exhaust Fan: Exhaust fan modulation must maintain building requirements.
Energy Recovery
Control of energy recovery equipment (heat wheel with/without VFD, core with face/bypass dampers, or bypass-only damper) is the third party's responsibility, controlled via a third-party provided sensor.
- Energy Wheel Bypass Damper: Open when exceeding design outdoor airflow in economizer mode by turning off the energy recovery wheel.
- Energy Core Dampers:
- Face/Bypass Dampers: A 2-10V signal controls the face damper for energy recovery; the bypass damper is the inverse.
- Bypass Only Damper: A 2-10V signal controls the bypass damper. For 80% energy recovery, the signal should be 20% (2 volts).
Energy Recovery Defrost
Both forms of energy recovery require a defrost sequence provided by the third-party controller.
- Energy Recovery Wheel: Provide an exhaust air temperature sensor or heat wheel pressure differential sensor/switch if pre-heat is not installed. Exhaust air temperature must remain above 36°F, or differential pressure must be less than 1.5"wc when outside air is below 10°F.
- Energy Core: Provide an exhaust air temperature sensor if pre-heat is not installed. Exhaust air temperature must remain above 36°F.
- Electric Preheat: If a preheat device is installed for defrost, the third-party controller must ensure these conditions are met before enabling preheat:
- Outside Air Damper >= 30% open
- Supply Fan enabled
- Outdoor Air Temp < 10°F
Temperature
Heat-Cool Only Control requires the third party to make decisions for heating, cooling, dehumidifying, or economizing based on operating conditions and setpoints. Setpoints are communicated via hard-wired 2-10 VDC signals:
- Cooling: Cooling Coil Setpoint
- Dehumidifying: Cooling Coil and Supply Air Setpoints
- Heat Pump Heating: Supply Air Setpoint
- Heating: Supply Air Setpoint
The third-party controller must manage economizer and energy recovery capacity to meet current requirements. Analog output signals are sent via the terminal strip or directly to end devices. Refer to Appendix A for wiring schematics and terminal strip information.
- Cold Coil Temperature Control: The third-party controller sends a signal to control compressors, with setpoints ranging from 50°F to 75°F in cooling and dehumidification modes.
- Supply Air Temperature Control: For units with HGRH coils or heating, a Supply Air Temperature Setpoint input (50°F to 95°F) is provided for the third-party controller. The HGRH valve and heating devices will control to this setpoint. (A minimum setpoint of 60.0°F is advised for heat pump heating mode.)
- Supply Temperature Limits: The controller has adjustable high and low temperature limits that disable cooling or heating. The third party must maintain:
- Minimum Low Supply Temp Limit: 35°F
- Maximum High Supply Temp Limit: 120°F
- Mode Switching – Cooling vs Heating: When both heating and cooling are present, the third party determines the required mode. The Cooling/Heating Control Mode input (open for cooling, closed for heating) triggers a shutdown of current devices and switches modes after a timer expires.
- Mode Switching – Cooling vs Dehumidification: If a hot gas reheat coil is installed, the third party determines when hot gas reheat controls to the Supply Air Temperature Setpoint. The Cooling/Dehumidification Control Mode input (open for cooling only, closed for reheat) manages this.
Digital Status
The Heat-Cool Only terminal strip provides digital status information from installed devices:
- OUTSIDE AIR DAMPER ACTUATOR END SWITCH: Indicates if the outside air damper actuator has reached a specific open position.
- CONDENSATE OVERFLOW SWITCH: Indicates if the condensate drain pan is full, potentially causing overflow if refrigeration continues.
- ENERGY RECOVERY STATUS: Indicates if the energy recovery device is rotating or its bypass is open.
Digital Commands
- FIRE ALARM: Integrates the building fire alarm to disable airstream refrigerant leak detection response. All heating/cooling stops when this input is open. Shutdown of other third-party controlled devices is the third party's responsibility. This input affects the Global Alarm status.
- REMOTE START/STOP: Remotely starts or stops refrigeration and heating control. The input must be closed for cooling or heating operation.
- COOLING/DEHUMIDIFICATION CONTROL MODE: Determines if the unit is in cooling or dehumidification mode.
- COOLING/HEATING CONTROL MODE: Determines if the unit is in cooling or heating mode.
FILTER PRESSURE SWITCH
Indicates dirty filters when installed.
GLOBAL ALARM OUTPUT
Indicates an alarm condition in the Heat-Cool Only controller.
A2L SYSTEM RESPONSE
A standard hardwired system monitoring for refrigerant leaks, responding in two ways:
- Air Tunnel Leak: Unit overrides supply fan and damper operation to move stagnant refrigerant for dilution. Ignition sources are disabled, and compressor operation is stopped. The supply fan operates at the higher of minimum heat operation CFM or UL-required minimum airflow for dilution. Recirculation dampers force 100% recirculation. 100% outdoor air units force 100% outdoor air. Heat operation (electric post heat, indirect gas heat) is allowed. The building is responsible for energy wheel speed, frost control, and exhaust fans.
- Compressor Section Leak: Unit disables compressor operation and indirect gas heat. The airstream fan is not forced on, and heat operation is not allowed. If no indirect gas heater is present, no refrigerant sensor is in the compressor section.
Alarm outputs are available for monitoring and external actions like opening zone dampers, disabling duct-mounted electric resistance heaters, or enabling mechanical ventilation. These can be accessed via the building management system or hardwire mitigation system contacts.
Mitigation system response verification requires removing the A2L mitigation test jumper at start-up. Additional testing may be required by local code.
Refrigerant sensors initiate a safety sequence upon leak detection. Maintain sensors free of dust. Alarm status is available as an electronic signal and a relay dry contact. End-of-life results in a leak detected indication. Refer to the sensor's blink code for status (Solid green: power-up/self-test; Blinking green: normal operation; Solid red: alarm/gas detected; Blinking red: sensor fault/replace).
Operation of Unit
All Modes
The following conditions are required for the third party to enable unit operation in any mode:
- Remote Start Input: Closed
- Shutdown Input: Closed
- Damper Positioning: OAD/RAD End Switch Closed (when installed)
- Supply Fan Status: Closed
- Supply Fan Control: Not below 50.0% of full-load airflow
NOTE: These safety checks are the responsibility of the third-party controller and are not input to the controller.
Cooling
The following conditions are required for the third party to enable the unit and start compressors in cooling mode:
- Cooling/Dehumidification Control Input: Cooling mode (Open)
- Cooling/Heating Control Input: Cooling mode (Open)
- Outside Air Temperature: > Cooling Ambient Lockout (55.0°F) (adj.)
- Cooling Coil Leaving Air Temp: > Coil Low Temp Limit (42.0°F) (adj.)
- Refrigerant Pressure Switches: Closed (Both High and Low)
- Supply Air Temperature: > Minimum Low Supply Temp Limit (35.0°F)
- Cooling Coil Setpoint: 50 - 75°F scaled from 2-10vdc (Compressor staging)
Dehumidifying
NOTE: Hot Gas Reheat must be installed in the unit to utilize this functionality.
The following conditions are required for the controller to enable a unit in dehumidification mode:
- Cooling/Dehumidification Control Input: Dehumidification mode (Closed)
- Cooling/Heating Control Input: Cooling mode (Open)
- Outside Air Temperature: > Cooling Ambient Lockout (55.0°F) (adj.)
- Cooling Coil Leaving Air Temp: > Coil Low Temp Limit (42.0°F) (adj.)
- Refrigerant Pressure Switches: Closed (High and Low)
- Supply Air Temperature: > Minimum Low Supply Temp Limit (35.0°F)
- Supply Air Setpoint: 50 - 95°F scaled from 2-10vdc (HGRH valve modulation)
- Cooling Coil Setpoint: 50 - 75°F scaled from 2-10vdc (Compressor staging)
Heating
The following conditions are required for the controller to enable a unit in heating mode:
- Heating/Cooling Control Mode: Heating mode (Closed)
- Outside Air Temperature: < Heating Ambient Lockout (80.0°F) (adj.)
- Supply Air Temperature: < Maximum High Supply Temp Limit (120.0°F)
- Supply Air Setpoint Request: 50 - 95°F scaled from 2-10vdc
Heating - Heat Pump
The following conditions are required for the controller to enable a unit and start compressors in heating mode:
- Heating/Cooling Control Mode: Heating mode (closed) (Heat Pumps Only)
- Outside Air Temperature: < Heating Ambient Lockout (80.0°F) (adj.)
- Outside Air Temperature: > ASHP Low Ambient Lockout (17°F) (adj.) (ASHP only)
- Refrigerant Pressure Switches: Closed (High and low)
- Supply Air Temperature: < Maximum High Supply Temp Limit (120.0°F)
- Supply Air Setpoint Request: 50-95°F scaled from 2-10vdc
Appendices
Appendix A: Terminal Strip Wiring
The following table details the terminal strip wiring for Heat-Cool Only operation, serving as the wiring point for the third-party control device. Refer to unit schematics for additional information.
| Terminal | Terminal Type | Description/Device | Third Party IO Type |
|---|---|---|---|
| 50C (2) | Common | Common | |
| 501 | 0.0-10.0 VDC | Supply Fan Speed Input | Analog Command |
| 502 | 0.0-10.0 VDC | Exhaust Fan Speed Input | Analog Command |
| 503 | 0.0-10.0 VDC * | Energy Recovery Capacity Input * | Analog Command |
| 51C | Common from Controller | Common | |
| 511 | 2.0-10.0 VDC | Cooling Coil Temperature Setpoint Input | Analog Command |
| 512 | 2.0-10.0 VDC | Supply Air Temperature Setpoint Input | Analog Command |
| 60C (2) | Common | Common | |
| 601 | 2.0-10.0 VDC | Outside/Recirc Air Damper Signal | Analog Command |
| 602 | 24 VAC | Outside/Recirc Air Damper Actuator Power | Digital Command |
| 603 | 24 VAC | Supply Fan Start | Digital Command |
| 604 | 24 VAC | Exhaust Fan Start | Digital Command |
| 605 | 24 VAC | Energy Recovery Wheel Start | Digital Command |
| 606 | 24 VAC | Pre-Heater Enable | Digital Command |
| 607 | 24 VAC | Return/Exhaust Damper Actuator Power | Digital Command |
| 70P (2) | 24 VAC power or 24 VAC common from unit | Digital Command | |
| 701 | Building Fire Alarm | Digital Command | |
| 702 | See Wiring Diagram | Remote Start Input | Digital Command |
| 703 | Cooling(0)/Dehumidification(1) Control Mode | Digital Command | |
| 704 | Cooling(0)/Heating (1) Control Mode | Digital Command | |
| 80C (3) | Common | Common | |
| 801 | Global Alarm Output (Heat/Cool Alarms Only) | Digital Status | |
| 802 | Outside Air Damper End Switch (100% OA Units) | Digital Status | |
| 803 | Condensate Overflow Switch | Digital Status | |
| 804 | Energy Recovery Status | Digital Status | |
| 805 | Filter Pressure Switch | Digital Status | |
| 806 | Return/Exhaust Damper End Switch | Digital Status | |
| 90C (2) | Common | Common | |
| 901 (2) | 24 VAC | AFMS Power | 24 VAC |
| 902 | 0.0-10.0 VDC | Supply Airflow Measuring Station | Analog Feedback |
| 903 | 0.0-10.0 VDC | Exhaust Airflow Measuring Station | Analog Feedback |
| 904 | 0.0-10.0 VDC | Outdoor Airflow Measuring Station | Analog Feedback |
| 71 | R21 NC | Airstream Mitigation sequence active | Status - Alarm/off state is normal state |
| 72 | R21 Common | Airstream Mitigation sequence active | Common |
| 73 | R21 NO | Airstream Mitigation sequence active | Status - Alarm/off state is normal state |
| 74 | R23 NC | Indirect Gas Furnace lockout active | Status - Alarm/off state is normal state |
| 74 | R23 Common | Indirect Gas Furnace lockout active | Common |
| 76 | R23 NO | Indirect Gas Furnace lockout active | Status - Alarm/off state is normal state |
* This terminal position is for any energy recovery device, heat wheel, core with face/bypass dampers, or core with bypass only damper. The voltage for either core option is 2.0-10.0VDC.
Appendix B: Gas Furnace Limitations
Supply fan modulation must be limited to the minimum airflow based on unit size or 50% of design airflow, whichever is greater. When modulating gas furnace heating capacity, maintain a maximum temperature rise and minimum airflow for all units.
WARNING: Criteria must be met when controlling gas furnace staging and modulation to prevent improper combustion and unit damage. Airflow reduction is allowed only if supply air temperature does not exceed the max temp rise. Supply air temp must be monitored, and the furnace modulated to prevent over-firing at low airflows.
- Locate unit casing size, furnace MBH, and airflow supply direction for minimum airflow in CFM in the table below.
- Limit all gas furnaces to the greater of: minimum airflow in CFM, OR 50% of design airflow.
- Third-party controls will send a 2-10VDC signal for a supply air temperature setpoint between 50.0°F (10.0°C) and 95.0°F (35.0°C) in all modes.
- Third-party controls must have a high supply temperature limit of 120.0°F (48.8°C) to shut down all heating sources when supply air temperature is greater than or equal to this limit.
- Minimum Temp Rise of 20.0°F for all furnaces.
| Unit Casing Size | Furnace MBH | Bottom Discharge | Side Discharge | ||
|---|---|---|---|---|---|
| Max Temp Rise | Min Airflow CFM | Max Temp Rise | Min Airflow CFM | ||
| RV-20 | 75 | 100.0°F | 556 | 100.0°F | 556 |
| RVE-20 | 100 | 100.0°F | 741 | 100.0°F | 741 |
| 150 | 100.0°F | 1,111 | 100.0°F | 1,111 | |
| 200 | 100.0°F | 1,481 | 100.0°F | 1,481 | |
| RV-40 | 100 | 100.0°F | 741 | 100.0°F | 741 |
| RVE-40 | 200 | 100.0°F | 1,481 | 100.0°F | 1,481 |
| RVC-40 | 300 | 100.0°F | 2,222 | 100.0°F | 2,222 |
| RV-85 | 300 | 100.0°F | 2,222 | 100.0°F | 2,222 |
| RVE-85 | 400 | 100.0°F | 2,963 | 100.0°F | 2,963 |
| RVC-85 | 600 | 100.0°F | 3,704 | 100.0°F | 3,704 |
| RV-150 | 600 | 100.0°F | 4,444 | 100.0°F | 4,444 |
| RVE-150 | 800 | 100.0°F | 5,926 | 100.0°F | 5,926 |
| 1000 | 100.0°F | 7,407 | 100.0°F | 7,407 | |
| 1200 | 100.0°F | 8,889 | 100.0°F | 8,889 | |
| RV-220 | 800 | 100.0°F | 5,926 | 100.0°F | 5,926 |
| 1200 | 100.0°F | 8,889 | 100.0°F | 8,889 | |
| 1600 | 100.0°F | 11,852 | 100.0°F | 11,852 | |
| 2000 | 100.0°F | 14,814 | 100.0°F | 14,814 | |
Appendix C: Supply and Exhaust Airflow Calculations
If airflow monitoring for the outside air damper is installed, it can be one of two types of airflow, each with its own calculations and setup.
Supply and Exhaust Fan Models
The following table shows available supply and exhaust fan blade models and their corresponding K Factor. The third party needs to know the fan model number, quantity, and whether an airflow monitoring station was purchased.
| Manufacturer | Model Number | Fan Blade Material | Fan Blade Diameter | K Factor |
|---|---|---|---|---|
| Greenheck | PRM-450 | Aluminum | 450mm/18" | 1899 |
| Greenheck | PRM-560 | Aluminum | 560mm/22" | 2975 |
| Greenheck | PDL-355 | Aluminum | 355mm/14" | 1160 |
Supply and Exhaust Fan Airflow Measurement
The third-party controller can use transducer signals from the supply and/or exhaust fan and the airflow formula to determine current airflow.
FORMULA: CFM = k * √ (△P)
Where:
- △P = Differential Pressure (0.0-30.0 in. wc scaled from 0.0 to 10.0 VDC reading from transducer)
- k = K Factor (from table) * # of Fans
- √ = Square Root
NOTE: Supply and exhaust airflow are calculated separately. Only include fans of the same type in the calculation.
Appendix D: GreenTrol Airflow Calculations
GreenTrol Airflow Monitoring
The GreenTrol® airflow monitoring station uses advanced thermal dispersion technology. An integral LCD displays airflow measurement and device configuration. It accepts up to two airflow probes for averaging.
GreenTrol Airflow Monitor functions:
- LCD readout of measured airflow
- Dual airflow probe averaging
ANALOG OUTPUTS:
The airflow monitoring controller has two configurable analog outputs for transmitting airflow, temperature, or PID control. Outputs can be configured for 0-10VDC, 0-5VDC, or 2-10VDC. The controller is factory configured to use analog output 1 for outdoor airflow rate and analog output 2 for outdoor air temperature. The airflow monitoring output is wired to the customer terminal strip for Heat-Cool Only controls. Refer to the airflow controller's technical manual for configuration instructions and the Field Calibration Wizard.
FORMULA: Calculating airflow based on the analog output signal:
Airflow = (Signal Voltage - Minimum Voltage) / (Maximum Voltage - Minimum Voltage) * Full Scale Airflow
Our Commitment
As part of its commitment to continuous improvement, Greenheck reserves the right to change specifications without notice. Specific Greenheck product warranties are available on greenheck.com under product area tabs and in the Library under Warranties.
AMCA Publication 410-96, Safety Practices for Users and Installers of Industrial and Commercial Fans, provides additional safety information and can be obtained from AMCA International, Inc. at www.amca.org.
[Greenheck Logo] Building Value in Air.
Contact Information:
- Phone: 715.359.6171
- Fax: 715.355.2399
- Parts: 800.355.5354
- Email: gfcinfo@greenheck.com
- Website: www.greenheck.com
Document 486987 • Heat-Cool Only Controls for DOAS, Rev. 3 August 2025
Copyright 2025 © Greenheck Fan Corporation
