If your building feels stuffy, your energy bills are unusually high, or the air feels damp even when it shouldn’t, your economizer may not be working correctly. Economizers are designed to bring in fresh outside air and reduce the need for air conditioning when the outdoor conditions are just right. But when they fail, often silently, they can cause energy waste, indoor air issues, and even mold, without anyone realizing what’s going wrong.
At Harold Brothers Mechanical, we’ve helped hundreds of building owners and facility managers uncover hidden HVAC issues like these. With decades of experience in commercial mechanical systems, we know exactly where to look and how to fix problems before they become costly.
In this article, you’ll learn what an economizer is, how to tell if it’s not working, how to verify its performance, and what kinds of hidden outdoor air problems can result if it’s left unchecked.
Think of an economizer as your HVAC system’s shortcut to free cooling. When the air outside is cooler than the air inside, the economizer opens dampers to let in that cooler air, helping your building stay comfortable without relying on the AC. This saves money on energy, improves indoor air quality, and helps extend the life of your equipment.
But when an economizer breaks, or when sensors and dampers stop working properly, it may stop bringing in fresh air altogether. In some cases, it might do the opposite and bring in too much outdoor air, even when it’s hot or humid outside. These kinds of failures often go unnoticed until they start causing real problems indoors.
If your energy bills have been climbing even when the weather outside is mild, your economizer may be stuck closed. When indoor air feels stale or smells unpleasant, that could mean no fresh air is coming in at all. Some buildings with broken economizers also experience high humidity, especially when the system brings in outdoor air during warm, wet weather. You might also notice certain rooms feel colder or warmer than others, which can happen when dampers get stuck in the wrong position.
Start by finding the outdoor air damper, usually located in the rooftop unit or air handler. Turn on your fan or AC system and watch the damper. On a cool day (around 55°F or lower), it should be noticeably more open than on a hot day. If the damper doesn’t move at all, it may be stuck or broken.
Next, look at the economizer’s controller. Most systems use sensors and a control board to decide when to bring in outside air.
The controller should show its interpretation of current outdoor conditions. If it’s misreading the temperature or humidity, it may not open the damper when it should.
Use a thermometer to compare the temperature of the indoor return air and the outdoor air.
If the outdoor air is significantly cooler but the economizer isn't letting more in, there could be an issue with:
Many newer economizer systems display error codes to indicate faults like:
If you notice blinking lights or unfamiliar codes, refer to the unit's manual or contact a technician to interpret the issue.
Another big problem is poor indoor air quality. A malfunctioning economizer may stop bringing in enough outdoor air to dilute CO2 and indoor odors. When that happens, people may feel sleepy, unfocused, or complain about the air being “off.” This matters even more in places like schools, offices, or medical facilities where good air is critical for health and productivity.
Even if you don’t notice moisture or air quality problems, a broken economizer can cost you. If it brings in hot air when it shouldn’t, or fails to bring in free cool air when it could, your AC runs more than it should. That leads to higher energy bills and more wear and tear on your system.
You should inspect your economizer at least once a year, ideally before the cooling season starts. If your building serves sensitive areas like hospitals, schools, or labs, twice a year is even better. Economizers are one of the most commonly overlooked HVAC components, but they’re also one of the easiest to test when you know what to look for.
Some buildings with automation systems can set up alerts that flag problems with outdoor air flow or damper positions. But even without automation, simple checks with a flashlight and thermometer can reveal a lot.
You don’t need fancy tools to test your economizer. A basic digital or infrared thermometer can help you compare air temperatures. A flashlight makes it easier to see damp movement. If you’re comfortable using a clamp meter, you can check the actuator motor’s amperage to see if it’s running. And for many commercial buildings, a service technician with HVAC control experience can take deeper readings and make adjustments.
Broken or misbehaving economizers often go unnoticed until they start causing comfort problems or costly energy waste. If your building has felt off lately, whether that means rising humidity, strange odors, or inconsistent temperatures, it’s time to take a closer look at your economizer. Even a few simple tests can uncover hidden issues that could be costing you more than you think.
At Harold Brothers Mechanical, we’ve helped countless facility managers uncover inefficiencies hiding in plain sight, and economizers are often one of the biggest culprits. Whether you’re dealing with an older rooftop unit or a modern BMS system, our team knows how to pinpoint problems before they affect your comfort or your budget.
Ready to learn more? Read our next article: “Commercial BMS & Controls Optimization to Improve HVAC Performance,” where you’ll learn how to fine-tune your system for greater efficiency, comfort, and cost savings.