PV, HVAC and refrigeration diagnostic labs
One decision on screen at a time. Wrong turns get coached, not just marked. You do not finish until the root cause is confirmed and the repair is verified. Three labs are free — no account needed. The rest of the labs, lessons, exam banks and timed mocks are part of HVAC Technical Training — Paths A–D.
- Interactive decision labs
- Built by working technicians
- Path-based verifiable certificate
- Know which exam to book
- Worldwide online
PV pathway lab previews
Inverter ground-fault diagnostic
Trace the evidence from isolation and measurements to a defensible fault decision.
PV domain map versus the roof
Connect PV Associate knowledge domains to the work a technician sees on the roof and at the equipment.
HVAC and electrical crossover
Carry a disciplined electrical diagnostic method between refrigeration equipment and power-electronics systems.
Residential No-Cool — Split System Not Cooling
Homeowner says the air handler is blowing but the house has been getting warmer since yesterday afternoon.
Start the free lab →Residential No-Heat — Gas Furnace Short Cycling on Ignition
Homeowner reports intermittent no-heat. The furnace lights, runs for a few seconds, then shuts down and tries again.
Unlock with Paths A–D →Frozen Coil / Airflow Restriction
Homeowner says the system runs all day but barely cools, and the vents feel weak and cold-damp rather than cold and strong.
Unlock with Paths A–D →Residential Over- and Undercharge — Poor Cooling Call
Homeowner says the system runs all day and the house never gets below 78°F. Another contractor “topped it up” last month and it felt better for a week.
Unlock with Paths A–D →Superheat / Subcooling Decision
Walk-in cooler is running continuously and only reaching 42°F on a 35°F setpoint. Customer says it used to hold fine.
Unlock with Paths A–D →TXV Hunting — Temperature Swings
Walk-in cooler temperature keeps swinging — overshoots cold, then drifts warm, never settles. Customer says they already added charge and it did not help.
Unlock with Paths A–D →Condenser / High Head — Walk-in Cutting Out on High Pressure
Walk-in cooler is running warm and the compressor keeps cutting out on the high-pressure control. The site contact is convinced it just needs gas.
Unlock with Paths A–D →Rack — One Circuit Down (Case Group Warm)
Supermarket rack: one case group is running warm while the other five circuits hold temperature. The night manager wants gas added to the rack; someone on shift has suggested shutting the whole rack down to see if it is that one.
Unlock with Paths A–D →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.
Unlock with Paths A–D →Walk-in Cooler Not Holding Temperature
Walk-in cooler is running but product temperature is rising. Box is at 48°F, setpoint 35°F.
Start the free lab →Ice Machine Not Making Ice
Ice machine is running but producing little or no ice. Bin is nearly empty.
Unlock with Paths A–D →Reach-in / Prep Table Not Holding Temperature
Prep-table reach-in is warm. Product in the pan rail is above safe temperature.
Unlock with Paths A–D →Walk-in Freezer Defrost Fault
Walk-in freezer keeps icing up. Product temperature climbs a few degrees each day and the customer has been scraping the coil by hand.
Unlock with Paths A–D →Natural Refrigerant Safe-Handling Decision
You are called to a small commercial site that has a new hydrocarbon (R-290) reach-in and a CO₂ (R-744) system in the same building. You must decide safe working practice before starting diagnosis.
Unlock with Paths A–D →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.
Start the free lab →RTU Economizer Stuck — No Free Cooling
Rooftop unit is cooling, but energy use is high and the economizer never seems to bring in outdoor air even on mild days.
Unlock with Paths A–D →RTU High Static — Low Airflow and Poor Cooling
Retail space is warm at the back of the building. The RTU runs constantly and the store manager says the vents 'barely blow'.
Unlock with Paths A–D →RTU Gas Heat — No Heat / Ignition Fault
Rooftop unit is not heating. Thermostat is calling for heat. Blower may run, but there is no useful heat from the supply.
Unlock with Paths A–D →RTU First Start-up Sequence
New packaged RTU has been set on the curb. Electrical and duct connections are complete. You are called to perform first start-up and basic verification before handover.
Unlock with Paths A–D →No Cool, First Call — Work the Order
“It stopped cooling sometime yesterday. The fan blows but the air is room temperature.”
Start the free lab →Running But Only 8°F Split
“It runs all day and the house never really gets cold. It used to shut off by lunchtime.”
Unlock with Paths A–D →28°F Split, Weak Air at the Registers
“The air coming out is freezing but the bedrooms never cool down.”
Unlock with Paths A–D →Condenser Dead, Indoor Blower Running
“The inside fan runs but the box outside never comes on anymore.”
Unlock with Paths A–D →Ice on the Suction Line, Filter Black
“There is ice all over the copper at the outdoor unit and water dripping in the closet.”
Unlock with Paths A–D →Short-Cycling After a Capacitor Swap
“Another company put a capacitor in last week. Now it starts, runs a minute, and clicks off.”
Unlock with Paths A–D →Heat Pump Running on Strip Heat Only
“The house stays warm but the electric bill doubled. The little heater light is on all the time.”
Unlock with Paths A–D →Inverter Mini-Split (R-32) Will Not Pull the Room Down
“The head runs all the time but the office sits at 28°C. It was fine last summer.”
Start the free lab →Communicating RTU — No Cool, No Fault Code
“The front half of the store is warm. The unit says everything is normal on the display.”
Unlock with Paths A–D →Occupied Retail, Warm Air, “The Last Tech Said It Was Fine”
“Two techs have been out. Both said it is working correctly. My staff are standing in 29°C.”
Unlock with Paths A–D →Leak Smell on a Current-Refrigerant System
“There is a sharp smell in the plant room and the unit keeps tripping. Can you just braze it up today?”
Unlock with Paths A–D →Commissioning Day — Drawings Versus As-Built
“We need the start-up sheet signed today so the fit-out can hand over.”
Unlock with Paths A–D →