Installation: Aspen A2L Refrigerant Detection System Instruction Manual

Overview

The A2L Refrigerant Detection System is a field-installed safety system for HVAC equipment using mildly flammable A2L refrigerant. It monitors the air inside the evaporator coil cabinet and initiates a mitigation response if the sensor detects a refrigerant-related fault or loses communication.

Installation, wiring, and commissioning must be completed by an A2L-trained and licensed HVAC contractor. The system connects the refrigerant sensor, mitigation control board, indoor blower, compressor controls, thermostat wiring, and—when equipped—the accessory control relay.

Specifications

• System type: Field-mounted A2L refrigerant detection and mitigation system
• Main components: Refrigerant sensor, sensor bracket, sensor cable, mitigation control enclosure, mitigation control board, and wire harness
• Available configurations: Standard Mitigation Kit, Option “S,” and Mitigation with Accessory Control Kit, Option “R”
• Mitigation enclosure location: On a nearby flat, vertical surface within 3 feet of the furnace
• Required sensor port: SENSOR1
• SENSOR2 use: Only for applications with two indoor units and an additional sensor connection
• Required casing access opening, when needed: 0.875 inch
• Minimum blower mitigation period after a detected fault: 5 minutes
• Normal startup indication: STATUS LED solid on during Warm-Up, then solid off during Run mode
• Communication fault indication: STATUS LED blinks twice repeatedly

Detailed Description

The refrigerant sensor is mounted on a bracket positioned near the evaporator coil and drain pan. Its sensing location allows the control system to monitor airborne refrigerant within the coil cabinet. A dedicated sensor cable carries the sensor signal to the mitigation control board.

The mitigation control board processes the sensor information and communicates with the connected HVAC equipment. In a fault condition, it deactivates the compressor and energizes the indoor blower to move air through the system. The blower remains active for at least five minutes after the initial fault is detected.

Option “R” adds an accessory control relay. Depending on the wiring arrangement, this relay can de-energize heating calls or control connected equipment such as electric heat, gas heat, air cleaners, or other accessories during mitigation.

Safety

• Only an A2L-trained and licensed HVAC contractor should install, wire, test, or service the system.
• Turn system power off before connecting or disconnecting the sensor from the mitigation control board.
• Never connect the sensor while the mitigation board is energized.
• Use only the SENSOR1 port for a single-indoor-unit installation.
• Do not mount the mitigation enclosure on the outside of the furnace or evaporator coil casing.
• Keep the enclosure away from furnace flue pipes and other sources of excessive heat.
• Protect the sensor cable from sharp casing edges by using the supplied strain relief.
• Create a drip loop in the sensor harness so condensation cannot travel into the sensor connection.
• Do not complete HVAC commissioning until every installation and system-test step has passed.
• Keep the A2L warning labels visible so future service technicians know that the system contains A2L refrigerant.

Setup and Installation

Prepare the Evaporator Coil

For a cased A-coil, remove the front casing panels to expose the evaporator coil. For an uncased coil, slide the coil into the field-provided casing. For a slab coil, remove the side panel on the refrigerant-piping side. Dedicated horizontal and plenum coil installations can proceed directly to sensor-bracket placement.

Before brazing, slide the two red discs over the liquid and suction lines and move them away from the brazing area. Follow the coil installation instructions for brazing and evaporator-coil installation.

Install the Sensor

Attach the sensor bracket to the drain pan in the position specified for the coil configuration. Keep the bracket vertical. The arrow marked on the refrigerant sensor must point upward.

Choose the approved sensor location that provides the shortest practical distance to the appropriate coil area. The sensor must be positioned as shown for the applicable vertical, upflow, horizontal, slab, flat, or dedicated-plenum configuration.

Route the Sensor Cable

Pass the sensor cable through a side opening in the coil casing whenever possible. If both side openings are blocked, create a 0.875-inch opening in the front casing panel. Install the supplied strain relief in the opening before routing the cable.

Form a downward drip loop in the cable below the sensor connection. Secure the loop with the supplied zip ties. This prevents condensation from following the harness into the connector.

Mount the Mitigation Enclosure

Install the mitigation control enclosure on a flat, vertical surface near the coil. Use the supplied two-sided tape or suitable field-supplied screws. The enclosure must be mounted flush and perpendicular to the mounting surface, within 3 feet of the furnace.

Do not attach the enclosure to the furnace exterior or evaporator coil casing. Keep it clear of furnace flue pipes and provide enough access to remove the cover for wiring and testing.

Connect the Wiring

With system power off, connect the sensor cable to the SENSOR1 port on the mitigation control board. Connect the low-voltage harness to the existing or newly installed furnace, thermostat, outdoor-unit, and blower wiring according to the wiring diagram for the installed system.

• Red wire: Indoor, furnace, or thermostat 24-volt hot connection, R
• White wire from the mitigation control board: Indoor, furnace, or thermostat Y1 connection
• White wire to the outdoor contactor: Outdoor contactor, CC
• Green wire: Indoor, furnace, or thermostat fan connection
• Brown wire: Indoor, furnace, or thermostat 24-volt common connection, C
• Gray wire from the relay: Indoor, furnace, or thermostat Y1 connection when the accessory-control arrangement requires it

For Option “R,” connect the accessory relay and harness according to the applicable relay diagram. Relay terminals 3, 4, 11, and 12 may be used for connected heating equipment, air-cleaning equipment, or other approved accessories, depending on the installation design.

Apply Warning Labels and Finish the Coil Installation

For uncased coils, apply the supplied warning labels to the casing where they are visible from the front. Labels for cased A-coils, dedicated or plenum coils, and slab coils are applied at the factory.

Close and secure the casing around the evaporator coil. Move the red discs so they sit just outside the coil cabinet. For dedicated horizontal or plenum coils, install the disc on the refrigerant lines before brazing the field piping.

System Test and Operation

A complete leakage-mitigation test is mandatory for every installation. Test Cooling for air conditioners and heat pumps, Heating for heat pumps, Electric Heating, and Fan operation separately. The HVAC system must be operating normally in the selected mode before each test begins.

Normal Startup

1. Confirm that the sensor is connected to SENSOR1 before applying power.
2. Power the mitigation system and allow approximately 10 seconds for communication to begin.
3. Verify that the STATUS LED is solid on, indicating Warm-Up mode.
4. Wait another 20 to 30 seconds.
5. Verify that the STATUS LED turns off, indicating Run mode.

If the sensor is missing when the system is powered, the control can enter mitigation mode and remain there for at least five minutes, including after power is cycled. Connecting the sensor before startup helps prevent this condition.

Option “S” Standard Mitigation Test

1. Open the enclosure to access the mitigation control board.
2. Confirm that the system has reached Run mode.
3. Turn system power off before disconnecting the sensor.
4. Squeeze the connector tab and remove the sensor cable from SENSOR1.
5. Restore power and wait approximately 15 seconds.
6. Verify that the STATUS LED blinks twice repeatedly, indicating a communication fault.
7. Confirm that the compressor is deactivated and the indoor blower starts.
8. Verify that the blower remains on for at least five minutes from initial fault detection.
9. Turn system power off, reconnect the sensor to SENSOR1, and restore power.
10. Verify Warm-Up mode with a solid STATUS LED, followed by Run mode with the STATUS LED off after 20 to 30 seconds.

The manual-reset function is disabled in the auto-reset arrangement used for the applicable standard mitigation system. Allowing the full five-minute sequence to expire is recommended before concluding the test.

Option “R” Accessory-Control Test

1. Remove the enclosure’s two screws and metal cover to access the mitigation board and accessory relay.
2. Place the thermostat in the operating mode being tested and verify normal HVAC operation.
3. Confirm the sensor is in Run mode before beginning the simulated fault.
4. Turn system power off, then disconnect the sensor cable from SENSOR1.
5. Restore power and wait approximately 15 seconds.
6. Verify the repeated two-blink communication-fault indication.
7. Confirm that the compressor is deactivated.
8. Verify that the connected accessory or heating equipment responds according to the relay wiring arrangement.
9. Confirm that the indoor blower starts and remains on for at least five minutes.
10. Turn system power off, reconnect the sensor to SENSOR1, and restore power.
11. Verify Warm-Up mode, then confirm Run mode after 20 to 30 seconds.

A loss of communication between the control board and sensor also produces the mitigation state. The system will not recover until communication is restored and the normal startup sequence has been completed.

Troubleshooting

STATUS LED Does Not Reach Run Mode

• Turn off system power before handling the sensor connector.
• Confirm that the sensor cable is fully inserted into SENSOR1.
• Inspect the connector for damage, loose pins, or an incorrectly routed cable.
• Check that the sensor arrow points upward and that the sensor is securely mounted.
• Restore power and allow the full Warm-Up period before evaluating the LED.

Two-Blip Communication Fault

• Verify that the sensor is connected to SENSOR1 rather than SENSOR2.
• Inspect the sensor cable along its entire route for cuts, pinching, or strain at the casing opening.
• Confirm that a drip loop is present and that moisture has not entered the connector.
• Turn system power off, reconnect the sensor, and repeat the startup verification.
• Do not continue commissioning if the fault returns.

Blower Does Not Start During the Test

• Recheck the low-voltage wiring against the diagram for the installed HVAC system.
• Confirm that the selected thermostat mode was operating normally before the test.
• Inspect the indoor fan connection and related control wiring.
• For Option “R,” verify the accessory relay wiring and terminal assignments.
• Resolve the wiring or control problem before placing the equipment into service.

Mitigation Sequence Will Not Clear

• Allow at least five minutes for the mitigation period after the initial fault.
• Turn system power off before reconnecting the sensor.
• Reconnect the sensor to SENSOR1 and restore power.
• Confirm that the STATUS LED progresses from Warm-Up to Run mode.
• If the system does not recover, recheck the complete wiring diagram and sensor connection before commissioning.

Pros & Cons

• Pros: Provides automatic refrigerant monitoring, disables compressor operation during a mitigation event, runs the indoor blower for at least five minutes, and supports optional accessory control.
• Pros: Includes visual startup and fault indications through the STATUS LED.
• Pros: Supports multiple evaporator-coil arrangements when the sensor bracket and cable are installed correctly.
• Cons: Requires qualified A2L-trained HVAC installation and detailed low-voltage wiring.
• Cons: The system cannot be commissioned until every operating mode passes the required test.
• Cons: Incorrect sensor connection, moisture intrusion, or loss of communication can place the system into a mitigation state for at least five minutes.