Rooftop Unit Not Cooling
Retail space is warm. Thermostat is calling for cooling, the supply fan runs, but the air out of the diffusers is not cold. Unit: 5-ton packaged rooftop unit, R-410A, single-stage cooling, gas heat section, economizer fitted. This is one of three free graded decision labs from Commercial HVAC / RTU — you choose each next check, readings fill in as you work, wrong turns are coached, and you are scored on cause, efficiency, safety and verification. No login required, about 15 minutes.
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- Exam preparation only
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Nameplate: 400 V 3-phase · 50 Hz · AS/NZS 3000. Working temperatures on this track are °C.
The call
Retail space is warm. Thermostat is calling for cooling, the supply fan runs, but the air out of the diffusers is not cold.
- Equipment
- 5-ton packaged rooftop unit, R-410A, single-stage cooling, gas heat section, economizer fitted
- Ambient
- 96°F
- Site notes
- Unit is on a flat roof with a parapet close to the condenser. Filters were changed last month.
Decision 1 of 5
You are on the roof with the panels still on. The supply fan is running.
What is your first move?
This is one of three free labs
Three free diagnostic labs. HVAC Technical Training — Paths A–D unlocks the remaining labs, lessons, full exam banks, timed mocks, and the Academy certificate. We do not issue EPA 608 or NATE credentials.
90 days of graded labs and mocks from enrolment. Your Academy certificate stays verifiable after that. Official exam fees are paid to the issuing body, not us. Access is not a licence and not lifetime.
Where this lab sits
This is one module lab from Commercial HVAC / RTU. The full path builds the rest of the diagnostic sequence around it, each module ending in a graded lab like this one.
Studying for an exam too?
Free practice questions with explained answers, then come back to the labs. Exam preparation only — we do not issue EPA, NATE or other official credentials.
All diagnostic labs
- Residential No-Cool — Split System Not Cooling
- Residential No-Heat — Gas Furnace Short Cycling on Ignition
- Frozen Coil / Airflow Restriction
- Residential Over- and Undercharge — Poor Cooling Call
- Superheat / Subcooling Decision
- TXV Hunting — Temperature Swings
- Condenser / High Head — Walk-in Cutting Out on High Pressure
- Rack — One Circuit Down (Case Group Warm)
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- Natural Refrigerant Safe-Handling Decision
- RTU Economizer Stuck — No Free Cooling
- RTU High Static — Low Airflow and Poor Cooling
- RTU Gas Heat — No Heat / Ignition Fault
- RTU First Start-up Sequence
- No Cool, First Call — Work the Order
- Running But Only 8°F Split
- 28°F Split, Weak Air at the Registers
- Condenser Dead, Indoor Blower Running
- Ice on the Suction Line, Filter Black
- Short-Cycling After a Capacitor Swap
- Heat Pump Running on Strip Heat Only
- Inverter Mini-Split (R-32) Will Not Pull the Room Down
- Communicating RTU — No Cool, No Fault Code
- Occupied Retail, Warm Air, “The Last Tech Said It Was Fine”
- Leak Smell on a Current-Refrigerant System
- Commissioning Day — Drawings Versus As-Built