A2L Safe-Handling Decision (R-454B)
A no-cool call at a small mixed site. One new split system is on an A2L refrigerant, the two older units are legacy A1. You must set safe working practice before you open anything. Unit: New R-454B split system alongside older R-410A equipment. This is a free graded decision lab from Residential HVAC — 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.
- Interactive decision labs
- Built by working technicians
- Path-based verifiable certificate
- Exam preparation only
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The call
A no-cool call at a small mixed site. One new split system is on an A2L refrigerant, the two older units are legacy A1. You must set safe working practice before you open anything.
- Equipment
- New R-454B split system alongside older R-410A equipment
- Ambient
- 91°F
- Site notes
- Air handler sits in a tight interior closet with poor ventilation. A gas water heater with a standing pilot is in the same closet. Recovery machine on the van is an older A1-only unit.
Decision 1 of 5
The nameplate and the equipment labels are within reach, and the closet door is currently closed.
Before opening any circuit, what do you do first?
Where this lab sits
This is one module lab from Residential HVAC. 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 free diagnostic labs
- Residential No-Cool — Split System Not Cooling
- Residential No-Heat — Gas Furnace Short Cycling on Ignition
- Frozen Coil / Airflow Restriction
- Superheat / Subcooling Decision
- 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