What Are the Two Control Modes for the GREE FLEXX ULTRA R32?

The GREE FLEXX ULTRA R32 (FXU R32) supports two control methods: RS485 communicating control and 24V control. RS485 is how the system was designed to run, using the controller that ships with the unit. 24V control uses either that same GREE controller switched to 24V or a third-party heat pump thermostat.

RS485 is a means of communication, not a specific product. Different GREE platforms use different communication circuits: GMV commercial equipment uses CAN bus, the FXU R32 uses RS485, and mini splits use an L1/L2 higher-voltage communication line. The FXU R32 will function either way, but communicating control gives the system the most information to work with.

Note: you cannot substitute just any RS485 controller. You must use the GREE RS485 controller that comes with the unit.

How Do You Set the RS485 vs 24V Dip Switch?

SA1 dip switch #1 selects RS485 versus 24V, and there is an SA1 bank on both the indoor and the outdoor unit. From the factory, both SA1 #1 switches are OFF, which sets the unit for RS485 with the included controller. As long as H1 and H2 are connected, you do not have to move the dip switches at all.

To run hard 24V without H1/H2 connected, set SA1 #1 to ON at both the indoor and the outdoor unit. The indoor and outdoor SA1 #1 must always be set the same.

• Always power off before changing dip switches. The board only reads the switch positions on power-up. If you change a switch while powered, turn the power off, wait, and power back on so it re-reads the setting.
• Go by the word ON, not up or down. The switch banks can be mounted vertical, horizontal, or upside down. Set the switch toward the printed word ON; if it is not on ON, it is off.

SA1 #1 dip switch (indoor and outdoor):

What Are the H1/H2 Communication Wires, and Should You Always Run Them?

H1 and H2 are the RS485 communication wires that run between the indoor and outdoor unit. Running them is recommended even in 24V control, because they let the outdoor unit (the main board that holds the operating program) see indoor data such as return air temperature and the inlet and outlet coil temperatures. With that data, it can set the run rate of both the indoor and outdoor unit more accurately.

When you run straight 24V with the dip switches flipped, you give the outdoor unit a hard 24V on/off signal and it loses set-point visibility. This is the same trade-off as a 24V adapter on a mini split: the adapter tells the machine to run but cannot pass the set point, so the unit defaults to a fixed (about 61 degree) target every call and ramps to a higher capacity than needed, hurting efficiency.

Flipping the dip switches only removes set-point visibility. The outdoor unit can still see return air temperature and the inlet and outlet coil temperatures, which is why keeping H1/H2 connected is worthwhile.

H1/H2 also support the GREE service tool. With the wires run, the indoor and outdoor units each provide a service-tool connector (a pigtail), so you can connect the tool without plugging into each unit separately.

Why Run H1/H2 in a Separate Cable?

Run H1/H2 in a separate cable from the 24V wiring because H1/H2 is communication wire, not power wire. If 24V crosses into the communication circuit through a damaged wire, a short, or a miswire, you can destroy the control boards.

• Use a separate 18/2 cable for H1/H2. The conductor can be 18/2 thermostat wire, solid or stranded, either one works.
• Two H1/H2 wires shorting together for a few seconds does not damage the communication circuit. Sending 24V into that line is what can damage the communication function of the boards.

How Do You Wire the RS485 (Communicating) Controller?

For RS485 control, run R and C from the indoor unit to both the outdoor unit and the controller (R and C power the controller), plus H1 and H2 from the indoor unit to the outdoor unit and from the indoor unit to the controller.

• Power for the controller: R and C feed the controller. R and C also run to the outdoor unit.
• Outdoor R/C: In lab testing the unit still functioned with the outdoor R/C disconnected when H1/H2 were connected, but GREE still recommends connecting R and C to the outdoor unit. Treat disconnecting it as unsupported.
• Heat kit jumper: If you have a heat kit, jumper R to W2. On RS485 this does NOT run electric heat continuously; the controller cycles the heat. This jumper is for RS485 only. Do not jumper R to W2 on a 24V install.

How Do You Wire the FLEXX Ultra R32 for 24V Control?

For 24V control, leave H1/H2 connected (recommended) and you do not need to flip the dip switches. Wire it like a typical heat pump: R to R, plus C and B, where B energizes the reversing valve in heat mode. On a third-party thermostat, switch the reversing-valve output from O to B.

Key 24V terminals:

• Y and Y1: Y from the thermostat to the air handler is the input. Y1 from the air handler to the outdoor unit Y is the output. On a refrigerant alarm, a set of contacts opens between Y and Y1 and drops the 24V to the outdoor unit, shutting the unit down immediately.
• L: The L terminal carries the alarm / refrigerant-leak signal. In 24V operation it signals the outdoor unit L terminal to display the error code. With a third-party thermostat, do not hook up L at the thermostat if that terminal is an output, because output-to-output causes damage.
• D: The D terminal is a 24V output that energizes during defrost. Wire D to D on a GREE air handler to shut the blower off during defrost, or wire D from the outdoor unit to W to bring on backup electric heat during defrost. You can also leave it unwired. The FXU and FXE air handlers have both a D and a W terminal.

What Is the Temperature Swing Difference Between RS485 and 24V?

In RS485 communicating mode the controller currently uses a 4 degree off / 1 degree on differential, so in cooling a 75 degree set point can cool to about 71 before the unit resumes. In 24V mode the differential is tighter at 2 degrees off / 1 degree on. GREE is working on an update to bring the communicating differential down to the same 2 / 1, possibly delivered as an over-the-air Wi-Fi update rather than a controller swap.

• The temperature-swing fix lives in the outdoor board program, not the controller. Units with a date code of November 13, 2025 or later (serial 4725 GS or after) have the corrected program.
• Putting a newer controller on an older outdoor board will not resolve the swing, because the program is in the outdoor board.

Should You Keep the RS485 Controller When Using a Third-Party Thermostat?

Yes. Keep the RS485 controller with the job even when the homeowner wants a third-party 24V thermostat. As long as the H1/H2 wires are run between the indoor and outdoor unit, you can connect the controller later and use it as a diagnostic tool without changing any wiring.

The controller reads about 20 parameters, including compressor frequency, indoor fan RPM, indoor coil temperature, return and supply air temperatures, and outdoor condenser coil temperature. With the indoor and outdoor coil temperatures and a PT chart you can derive your high and low pressures, which can sometimes save you from putting gauges on the system. You can connect it right at the condenser if you prefer to stay outside.

Outdoor SA1 Dip Switch #2: Air Handler vs Coil (RS485 Only)

On the outdoor unit, SA1 dip switch #2 tells the unit whether it is paired with an air handler or an AC coil. This designation only applies when you are using RS485 communication.

Frequently Asked Questions

Is the GREE FLEXX ULTRA R32 set to RS485 or 24V control out of the box?

The FLEXX ULTRA R32 ships set to RS485 communicating control. From the factory, both the indoor and outdoor SA1 dip switch #1 are OFF, which is the RS485 setting for use with the included wired controller.

Do I have to change the SA1 dip switches to run 24V control?

Not if H1/H2 are connected: leave SA1 #1 OFF at both units and the system runs 24V control while H1/H2 keeps passing data. Only if you are running hard 24V without H1/H2 do you need to set SA1 #1 to ON at both the indoor and outdoor unit, and the indoor and outdoor switches must always match. Always power the unit off before changing a dip switch, since the board only reads switch position on power-up.

Can I use any RS485 controller with the FLEXX ULTRA R32?

No. You must use the GREE RS485 controller that ships with the unit. You cannot substitute a different RS485 controller.

Can H1/H2 communication wire and 24V wiring share the same cable?

No. Run H1/H2 in a separate cable from any 24V wiring, because H1/H2 is communication wire, not power wire. If 24V crosses into the communication circuit through a damaged wire, a short, or a miswire, it can destroy the control boards. Two H1/H2 wires shorting together for a few seconds does not damage the communication circuit; it is 24V getting into that line that causes the damage.

What type of wire should I use for H1/H2?

Use a separate 18/2 cable for H1/H2. The conductor can be 18/2 thermostat wire, and either solid or stranded conductor works.

Do I need to jumper R to W2 for a heat kit?

Only on an RS485 install with a heat kit: jumper R to W2 and the controller will cycle the electric heat rather than run it continuously. This jumper is for RS485 only; do not jumper R to W2 on a 24V install.

Why does my RS485 communicating unit swing about 4 degrees before cycling back on?

In RS485 communicating mode the controller currently uses a 4 degree off / 1 degree on differential, so a 75 degree cooling set point can drift to about 71 before the unit resumes. GREE is working on an update to bring that differential down to match 24V mode’s tighter 2 degree off / 1 degree on setting. The fix lives in the outdoor unit’s board program, not the controller, so a newer controller on an older outdoor board will not resolve it. Units with a date code of November 13, 2025 or later (serial 4725 GS or after) have the corrected program.

Should I keep the RS485 controller on the job if the homeowner wants a third-party 24V thermostat?

Yes. Keep the RS485 controller with the job even when a third-party 24V thermostat is installed, as long as H1/H2 are run between the indoor and outdoor unit. You can connect the controller later without changing any wiring and use it as a diagnostic tool. It reads about 20 parameters, including compressor frequency, indoor fan RPM, indoor coil temperature, return and supply air temperatures, and outdoor condenser coil temperature.

What does SA1 dip switch #2 on the outdoor unit control?

SA1 dip switch #2 on the outdoor unit tells the system whether it is paired with an air handler or an AC coil. This setting only applies when you are using RS485 communication.

For a deeper dive on GREE FLEXX Ultra R32 setup, wiring, dip switch settings and controls, check out the full instructional video: