Minimum position
Slightly open. Just enough outside air for ventilation; the rest is return air cooled by the compressor.
- Overview
- Economizers
Is your rooftop unit's economizer working?
An economizer lets a rooftop unit cool with outside air when the air outside is cool enough. When its damper sticks, the unit either wastes that free cooling or pulls in hot air on the hottest days. Here's how it should behave.
Three positions of the damper.
Simplified drawings of a rooftop unit's outside-air damper. Real units also have a relief damper, filters and a coil.
Full economizer
Wide open. Cool outside air does most of the cooling, and the compressor rests. This is the "free cooling".
Closed
Shut when the building is unoccupied. Stuck shut while people are inside means no free cooling and too little fresh air.
What goes wrong.
Economizer faults are common on small commercial units, and they rarely stop the unit — so nobody notices.
| Fault | What you might notice | What it costs you |
|---|---|---|
| Damper stuck open | The space won't cool on hot afternoons; humid, warm air in summer | The compressor fights outside heat all day |
| Damper stuck shut | Stuffy rooms; nothing obvious | No free cooling; not enough fresh air |
| Failed actuator | The damper doesn't move at all | Either of the above |
| Bad sensor | The damper opens at the wrong times | Warm air brought in when it shouldn't be |
| Broken linkage | The actuator moves; the blades don't | Either of the above |
What we check
- Movement
- The damper driven through its full range and back.
- Minimum position
- Set so the space gets the fresh air it needs.
- Sensors
- Outside and return readings checked against a meter.
- Linkage & seals
- Tightened, lubricated or replaced.
- Alarms
- Many newer units in California have built-in fault detection for the economizer; we read and clear it.
And at home?
Most homes don't have economizers. The home version of the same idea is simply using cooler morning and evening air — opening up when it's cool outside, closing up before the heat. Residential service
Book an economizer check
We check economizers on every commercial maintenance visit. For a one-off check, send a request with the number of units.