No Cool, First Call — Work the Order
“It stopped cooling sometime yesterday. The fan blows but the air is room temperature.” Unit: 3-ton split system, 12 years old, communicating-capable thermostat replaced last spring. This is one of three free graded decision labs from Residential HVAC Service & Diagnostics — 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 12 minutes.
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Nameplate: 230 V 1-phase · 50 Hz · NEC / IS practice. Working temperatures on this track are °C.
The call
“It stopped cooling sometime yesterday. The fan blows but the air is room temperature.”
- Equipment
- 3-ton split system, 12 years old, communicating-capable thermostat replaced last spring
- Ambient
- 94°F
- Site notes
- Homeowner has already changed the filter and pushed the thermostat down to 65. Outdoor unit is quiet when you walk past it.
Decision 1 of 4
The blower is moving air, the room is 84°F and the thermostat display reads Cool 65. Nothing is happening outside.
Where do you start?
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 Residential HVAC Service & Diagnostics. 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)
- A2L Safe-Handling Decision (R-454B)
- Walk-in Cooler Not Holding Temperature
- Ice Machine Not Making Ice
- Reach-in / Prep Table Not Holding Temperature
- Walk-in Freezer Defrost Fault
- Natural Refrigerant Safe-Handling Decision
- Rooftop Unit Not Cooling
- 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
- 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