HVAC and Safety
Refrigeration cycle and airflow
The cycle is compressor, condenser, metering device, evaporator: the compressor raises pressure and temperature, the condenser rejects heat outdoors, the metering device drops pressure, and the evaporator absorbs heat indoors. Most cooling complaints trace to airflow or charge, in that order. Check the filter (monthly is the standard), return air path, blower, and evaporator coil before adding refrigerant. A measured 15-20 degree F temperature split between return and supply air indicates a normally operating system; a frozen coil or suction line points to low airflow, low charge, or a restriction, never to "just add refrigerant."
Heating and components
Gas furnace sequence: call for heat, draft inducer, ignition, flame proving, then blower delay. A dirty flame sensor causes short cycling. Heat pumps add a reversing valve, defrost cycle, and auxiliary or emergency heat, and electric strip heat draws high amperage. Verify combustion air and venting; a cracked heat exchanger is a carbon monoxide hazard and must be tagged out of service.
Refrigerant law and safety
Refrigerant is regulated under EPA Section 608: never vent it, certification is required to handle it, and cylinders stay upright, secured, and capped. Liquid refrigerant can cause frostbite. Safety underpins every domain: PPE, ladder and lift rules, lockout/tagout, SDS access, bloodborne pathogen precautions, fire extinguisher classes, and carbon monoxide response. For a gas odor, do not operate switches or phones inside; get everyone out first, then call.
Worked example
Warm air, cooling complaint: confirm the thermostat setting, replace a loaded filter, verify the outdoor unit and compressor are running, then measure the temperature split. If the filter is clean, the compressor runs, and the split is well below 15 degrees F, stop and call a certified technician rather than adding refrigerant.