How To Fix It

Why Dual Zone AC Not Working in One Zone? Troubleshooting Guide

A dual-zone AC is an investment and, of course, finding out that the cooling is not working in one of the zones can be devastating.

Issues with the thermostat, control panel, or dampers are the most common reasons for AC not working in one zone. You should also make sure that the unit is properly sized for the house – the area farthest from the team can’t be cooled properly if the equipment is undersized. 

Dual Zone AC Not Working in One Zone

The complicated technology of dual-zone ACs is quite vulnerable to the following issues:

Thermostat malfunction

In the absolute majority of cases, if there is something wrong with your AC in one of the zones, it’s the thermostat’s fault. Sometimes, all you would have to do is reset the device or change the batteries.

Also, make sure that you have chosen the perfect spot for the thermostat, and don’t forget to check the settings (someone might have changed them)

Read: Why Are HVAC Vents Under Windows?

Problems with the control panel

The control panel is the ‘brain’ of the whole system. If it’s unresponsive or is not turning on at all, then calling an expert might be the best possible decision.

Stuck dampers

Dampers are the elements that turn a regular HVAC system into a dual-zone one. However, the fact that these components move also means that they can get stuck in one position.

Usually, cleaning and lubricating the dampers would be enough to fix the issue, but it might be a challenging DIY project as the dampers can be located in the system’s ducts. 

Read: Why HVAC Maintenance Is Important?

Why Does My AC Only Work One Room?

  • The AC fan motor might not be working properly – the fan is the component that pushes the cool air through the ductwork, if it’s not able to do that, then the room that’s closer to the air conditioner will feel a lot cooler than the rest of the house
  • If the thermostat is misreading the temperature in certain areas of your house, then it might not make the AC turn on in the corresponding area
  • The damper that is ‘responsible’ for your HVAC system’s second zone might simply be stuck
  • Sometimes, an AC is not sized correctly – if the unit is too small for your home, it will struggle to cool the house evenly

Why Is My AC Not Cooling Certain Rooms?

Obstructed vents might be the root cause of the problem. This will happen if:

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  • The vent is closed
  • There is an obstruction in front of the vent – you should keep furniture at least 6 inches away 
  • There is an internal blockage – the ductwork might be dirty or an obstruction got stuck somewhere in the ducts

Read: Why Is HVAC Not Working?

What to Do If No Air Is Coming Out of Vents in One Room?

First of all, make sure that the vents in the room are fully open and that there are no obstructions in front of them. Also, check the air filter – it might be too dirty or clogged.

If there is no air coming out of the vents in a room that is farthest away from your HVAC unit, then the chances are high that the system is simply undersized.

Why Does My AC Work Downstairs but Not Upstairs?

Your AC might be working upstairs, but it’s struggling to maintain the desired temperature as hot air naturally rises (the upstairs unit would have to work a lot harder than the downstairs one).

If the thermostat and air filters are fine, then bad insulation might be to blame. Check the attic – improper insulation can’t keep the hot air out and the cool air in.

How Does a 2 Zone Air Conditioner Work?

The dampers are placed at the air outlet or inside the ducts and they are connected to create a separate zone.

Each zone, in its turn, is controlled by its thermostat. The dampers and the two thermostats in a dual-zone HVAC system are connected to the main control panel.

If one of the zones calls for heat or cool air, the dampers in this area will open, while the others will remain closed.

Read: Why HVAC Is Important

Can You Have 2 Zones with One AC Unit?

With a zoned system, a single AC unit would be able to provide cooling to the different areas in your house. You can choose to cool both of the zones simultaneously or lower the temperature in only one.

Do bear in mind, however, that if you have one unit responsible for all the zones in the house, you won’t be able to heat and cool different rooms in the building at the same time.

Read: Quietest HVAC System

How Do You Troubleshoot Zone Dampers?

If your dampers are not responding to the system’s signals, then it might be because they are stuck (simple cleaning would usually fix the issue) or because there is something wrong with the zoning board.

If none of those is the issue, then the dampers might have gone bad and you would have to replace them or the damper motor.


Where Are Zone Dampers Located?

Generally, you’ll find the dampers in the main trunk line (before and after the significant junctions). 

How Do You Increase Airflow in Air Ducts?

There are a few tips that’ll help you increase airflow in the ducts:

  • Find and seal the air leaks
  • Clean or replace the air filters
  • Clean out the ductwork
  • If your HVAC system does not have a fan speed regulator, then you can invest in an inline booster fan

Why Is Only Half My House Cooling?

  1. Some of the air vents are closed or blocked
  2. Your fan is not turned to ‘on’
  3. The ducts in one part of your house have leaks
  4. Your attic is not properly insulated

How Do I Know If My AC Vent Is Clogged?

  1. Turn your HVAC system on.
  2. Once the fan kicks in, check all the vents one by one.
  3. If there is a noticeable difference in the airflow through a certain vent, then the duct might be blocked.

Can One Thermostat Control Two Zones?

There are dual-zone thermostats that can control both zones in the house. In some zoned systems, you’ll find the ‘main’ thermostat that controls the other thermostat – it all depends on how your specific system was installed.

How Does a Multi-Zone Air Handling Unit Work?

There are zoned systems that would have an air handling unit with both a cooling and a heating coil. The supply air can be pushed either over the heating coil, the cooling coil, or both of them – this allows the unit to vary the temperature of the air to meet the requirements of each zone. 

What Is a Dump Zone in a Zoned Air System?

A dump zone is an area in the house where the duct doesn’t have a damper. This means that the room or rooms are going to receive airflow every time you turn the HVAC system on.

How Do You Balance an AC in a Two-Story House?

You can try lowering the temperature upstairs by around 2 degrees. Turning the fan setting to ‘on’ and installing window coverings can also help balance your AC in a two-story building.