RTU Economizer Stuck — No Free Cooling
- Interactive decision labs
- Built by working technicians
- Path-based verifiable certificate
- Exam preparation only
- Worldwide online
Commercial HVAC / RTU
~13 min
intermediate
The call
Rooftop unit is cooling, but energy use is high and the economizer never seems to bring in outdoor air even on mild days.
- Equipment
- 7.5-ton packaged RTU with dry-bulb economizer, R-410A, ~6 years old
- Ambient
- 58°F
- Site notes
- Outdoor temperature is well below return-air temperature. Thermostat is calling for cooling. Customer expects free cooling under these conditions.
Decision 1 of 4
It is a mild 58°F day and the unit is running mechanical cooling.
Outdoor air is 58°F and return is 74°F. What should a functioning dry-bulb economizer be doing?
Where this lab sits
This is one module lab from Commercial HVAC / RTU. The full path adds sealed systems, defrost, rack-system orientation and natural-refrigerant safety, each ending in a lab like this one.
Open the full pathNext lab: Residential No-Cool — Split System Not CoolingNext lab: Residential No-Heat — Gas Furnace Short Cycling on IgnitionNext lab: Frozen Coil / Airflow RestrictionNext lab: Superheat / Subcooling DecisionNext lab: Walk-in Cooler Not Holding TemperatureNext lab: Ice Machine Not Making IceNext lab: Reach-in / Prep Table Not Holding TemperatureNext lab: Walk-in Freezer Defrost FaultNext lab: Natural Refrigerant Safe-Handling DecisionNext lab: Rooftop Unit Not CoolingNext lab: RTU High Static — Low Airflow and Poor CoolingNext lab: RTU Gas Heat — No Heat / Ignition Fault