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ComfortStar Technical Bulletin 24V+485 AHU Wiring Connecting Guide – Scenario 1 (Recommend)

24V+485 AHU Wiring Connection Guide - Technical Bulletin No. TB230427-03
Scenario 1 (Recommended)

Learn how to correctly connect the AHU-SG2 Air Handler to a CPR or CPH Side Discharge Condensing Unit with the ComfortStar thermostat in Scenario 1 of the 24V+485 AHU Wiring Connection Guide (Technical Bulletin No. TB230427-03).

You can access this bulletin by clicking here or through the ComfortStar Tech Support Mobile App in the APP STORE or GOOGLE PLAY under technical bulletins.

  • In Scenario #1, connect the thermostat to HA and HB on the display board and the condenser cables to S1 and S2 on the main board of the AHU-SG2.
  • For the CPR or CPH Side Discharge Condensing Unit, attach S1 and S2 on the top terminal board, clearly marked.
  • Ensure all DIP switches are in the off position (switched to the bottom).
  • When the unit is powered on, the board should display 00.
  • Once the thermostat is activated, your settings will appear on the AHU-SG2 display board, and in Scenario 1, the blower motor will start running within seconds.
  • In this setup, the blower motor will run continuously even after the desired temperature is reached; only by physically turning off the thermostat can you stop the blower motor.

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EPA Proposes Ban on R-410A Systems Starting in 2025

EPA Proposes Ban on R-410A Systems Starting in 2025

This move is part of a larger effort to reduce the carbon footprint of the HVAC industry. While R-410A has been widely used as a refrigerant in air conditioning systems, it is a hydrofluorocarbon (HFC), which contributes to the depletion of the ozone layer and global warming. As such, the EPA has been encouraging the use of more environmentally friendly refrigerants, such as R-32 and R-290, which have a much lower GWP and are less harmful to the environment.

While the phase-out of R-410A may pose some challenges for the HVAC industry, it presents an opportunity for manufacturers to innovate and develop more sustainable solutions. It also presents an opportunity for building owners and operators to invest in more energy-efficient and eco-friendly HVAC systems, which can help reduce their carbon footprint and operating costs in the long run. Overall, the phase-out of R-410A is a positive step towards a more sustainable future. By reducing the use of harmful HFCs in air conditioning systems, we can help protect the environment and mitigate the impacts of climate change.

The reduction of HFC consumption is a significant step towards combating climate change. HFCs are potent greenhouse gases that contribute to global warming and the depletion of the ozone layer. By reducing the use of HFCs, the EPA/DOE plan aims to reduce carbon emissions and promote a healthier environment.

The plan also includes incentives for the development and use of alternative refrigerants that are less harmful to the environment. This will encourage innovation and investment in the HVAC industry, ultimately leading to more sustainable and eco-friendly solutions.

As for the SEER2 requirements, they will improve the energy efficiency of HVAC equipment, helping to reduce energy consumption and lower energy bills for homeowners and businesses. This will also have a positive impact on the environment, as less energy consumption means lower carbon emissions.

Overall, the EPA/DOE plan marks a significant milestone in the fight against climate change. By reducing HFC consumption and promoting energy efficiency, we can create a more sustainable future for ourselves and generations to come.

One way we can ensure that we continue to provide comfort for our customers is by being proactive about the changes in the HVAC industry. We understand that it can be difficult to keep up with all the changes and new regulations, which is why we are here to help. We want to make sure that our customers are aware of the new regulations regarding R410 refrigerant and how it could impact their HVAC systems. Our team of experts is available to answer any questions and provide guidance on how to prepare for this transition.

At the end of the day, our goal is to provide comfort at a great value, and that means staying up-to-date with the latest industry changes and trends. We are committed to helping our customers navigate this transition and ensuring that they continue to receive the highest level of comfort and service.

Using A2L refrigerants such as R32 and R454B as a replacement for R410A has been shown to have a significant impact on reducing greenhouse gas emissions. These refrigerants are also more energy efficient, which can help reduce energy costs for consumers. Choosing a system that uses A2L refrigerants can also have long-term benefits for the environment, as they have a lower global warming potential than other refrigerants. As we continue to prioritize environmental responsibility, is committed to providing reliable, efficient HVAC systems that meet or exceed SEER2 standards and comply with environmental regulations.

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One room’s too cold and another too hot — you need better temperature control for your home. HVAC systems give you the comfort and control you want. There comes a point, where you may wonder… if you should choose a single-zone or multi-zone HVAC system. Both options come with their own benefits, but ultimately, the one you should choose will depend on your specific situation.

If you aren’t sure which HVAC system you need, we’re here to help. Consider your home and needs and compare single-zone versus multi-zone HVAC systems with the below guide.


Customize Your Small Space for Optimal Comfort

What Is a Single-Zone System?

A single-zone HVAC system serves one area or room of your home. How does a single-zone HVAC system work? With a single unit, this system provides the same cooling or heating throughout an area to adjust the temperature. You could use a single-zone HVAC if:

  • You have an addition: When you add on to your house, the new area won’t be connected to the rest of your home’s HVAC. A single-zone system helps cool, heat and ventilate the new area.
  • You have an area that needs extra control: Your current HVAC system may under-serve some areas of your home. Attics and other rooms may be hotter or colder than you like. A single-zone system helps you better control those spots.
  • You have a garage or workshop: Some homeowners condition the air in a garage or workshop with a single-zone HVAC system instead of a window unit. Then, you can still use your windows for airflow while maintaining the temperature and ventilation.
  • You have a small home: Small cabins or other small homes may only need a single-zone system to stay comfortable. That’ll depend on the capacity of the system you’re considering. Just ensure you have adequate airflow with fans to distribute the air throughout your home.


Heat/Cool Multiple Living Spaces Independently Efficiently

What Is a Multi-Zone System?

A multi-zone HVAC system lets you cool, heat or ventilate multiple rooms in your home. But how does a multi-zone HVAC system work? Multiple units go throughout your home to serve different rooms or areas. You get independent control of the spaces within your house with this system because it creates different zones. You may want a multi-zone HVAC system if:

  • You have a large or multileveled home: With multiple levels or large square footage, your home needs more than one HVAC unit. A multi-zone system can accommodate most or all of the rooms and spaces of a larger house.
    • You have rooms with different needs: If an area of your house needs to be cooled more, like the kitchen, and other rooms need to be heated, like bedrooms, a multi-zone system helps you make those adjustments.
    • You live in an old house: An old house makes it challenging to install new ductwork. A multi-zone HVAC system does require installation, but it won’t be as invasive as running ducts through the walls since every room has its own unit.

Single-Zone vs. Multi-Zone HVAC Systems

To decide which system is best for you, you need to look primarily at your needs and home. If your house could use either a single– or multi-zone system, or you aren’t sure which suits your needs, compare the two solutions — from their advantages to the installation process.

Pros of Single-Zone and Multi-Zone HVAC Systems

No matter which system you choose, you’ll get the advantages of versatile applications and precise temperature control. From there, you can evaluate the pros of single-zone versus multi-zone HVAC systems since they come with different advantages. The benefits of single-zone HVAC include:

  • Lower cost: Because a single-zone system involves fewer components than a multi-zone installation, it makes sense that a single-zone option is cheaper. That doesn’t mean you should take the lower-cost route and get a single-zone system, though, especially if you have a larger home. But it is an added benefit when you do need a single-zone system.
  • Enhanced comfort: Whether you have an addition or an under-served home area, a single-zone HVAC helps you control its temperature. You won’t have an upstairs room that’s too hot or a downstairs room that’s too cold. Instead, you can enhance the comfort of a room or space in your home to your exact needs.
  • Efficient size: With a smaller space or home, a single-zone system is the way to go. A larger unit or traditional system will shut on and off more often as it won’t take long to adjust your space to the right temperature. That puts unnecessary wear and tear on the machine, meaning you’ll have to get maintenance and repairs more often.

While the pros of a single-zone installation are appealing, multi-zone options also come with their own advantages. The benefits of multi-zone HVAC include:

  • Energy efficiency: Be more efficient with your energy spending when you have a multi-zone system. You can adjust the temperature to be more efficient or turn off the HVAC completely in zones that cover unused parts of your home.
  • Better control: Traditional systems only accurately adjust the temperature in the room with the thermostat. A multi-zone system helps you control the temperature in any room or area with its own unit. That gives you better temperature control and accuracy throughout your house.
  • Customization: Better control means you can customize the temperature in every room. This custom comfort is particularly useful for bedrooms. Everyone likes to sleep in a room with a different temperature, and a multi-zone system lets you do that. That means everyone in your home will sleep comfortably with a multi-zone HVAC.

Single-Zone vs. Multi-Zone HVAC Installation

The installation process varies between these HVAC systems. Again, you shouldn’t compromise and choose one over the other just based on these factors. You’ll have to pick what’s best for your home, but understanding single-zone versus multi-zone HVAC installation will help you see the difference between the two options:

  • Single-zone: For a single-zone system, you have an outdoor and indoor unit. This setup is known as a one-to-one configuration, and it also includes a drain line, cable and line set.
  • Multi-zone: A multi-zone HVAC uses one outdoor unit and multiple indoor units. How many indoor units you need will vary with how many rooms or areas you want to control.

single zone



  • New Standard High Efficiency.
  • Perfect for achieving true-zoning in applications where thermal loads may vary within the same building/residence.
  • Capacity output is significantly higher than traditional units.
  • Indoor high-wall evaporator units are available from 9,000 BTUH to 36,000 BTUH.

multi zone


  • A single outdoor condensing unit can power up to 5 different indoor evaporators.
  • There are more than 249 possible combinations ranging from 9,000 BTUH to 36,000 BTUH in High-Wall Mounts and Multi-Position Air Handler Units offering contractors flexibility in system designing.

Now That You've Got This Far,
Contact A Local A/C Contractors for a New HVAC System

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With over 50 years of combined experience, our research and development team continues to develop products that adhere to the highest quality standards, while elevating the level of efficiency to protect our precious environment.

Our manufacturing facilities maintain the highest quality and reliability standards with ISO9001 and ISO14001. All our products are AHRI and ETL certified.  

Across the world, we are committed to bringing daily comfort into every facet of your lives. Whether it is your home, your child’s school, or your local grocery store, ComfortStar is there to ensure a pleasant environment, regardless of the climate.

Advances in Inverter technology have made mini-split heat pump systems among the highest efficiency heating and air conditioning systems on the market today. This technology allows us to modulate the frequency of a compressor according to the thermal load of the conditioned space; therefore, a compressor can reduce the amount of work it does to reach a desired set temperature.

This results in longer compressor life-span and most importantly, decrease in energy usage and increased energy savings.

Mini-splits are ideal when making additions to a home, since expanding existing duct work can be problematic in some situations. Ease of installation makes it very practical for light commercial applications, such as hotel rooms, office spaces, malls and hospitals.


Products Made With Industry Leading Innovation

Advances in Inverter Technology have made our mini-split heat pump systems among the highest efficiency heating and air conditioning systems on the market today.

We are proud to be recognized worldwide as a leader in providing reliable, energy-efficient, innovative, and cost-effective products.


🡆 R410a Systems: Environmental friendly refrigerant.
🡆 Inverter Controlled Compressor:
High efficiency variable speed compressor.
🡆 Gold Fin: Condenser Coil Coating enhances heat
exchange, improves hydrophilic performance and
protects against corrosion.
🡆 Active Carbon Electrostatic Fiber Filter:
Electrostatic fiber traps small dust particles, smoke and pet
dander to prevent allergies.
🡆 Built-In Low Ambient Control:
System can operate in cooling and heating mode even.
when ambient conditions decrease down to 5° F.
🡆 Follow-Me Remote Control:
Built-in sensor in remote control which measures
room temperature where the remote is located.