Which do I use — superheat or subcooling?

It depends on the metering device, not preference. Fixed-orifice systems are charged by superheat; TXV systems by subcooling. Identify the device first — the lab makes you do it before the gauges come out.

Can I charge correctly without checking airflow?

No. A dirty filter, matted coil, or weak blower distorts both readings. Prove airflow first or every later number is suspect.

Do target values change by country?

The physics does not change, but the units and nameplate conventions do. Work in the units on the equipment in front of you — the lab shows this region's nameplate readings.

Superheat vs subcooling — what to do before you charge

Superheat says one thing, subcooling says another, and the refrigerant cylinder is already in your hand. Charging on a hunch is the most expensive guess in residential air conditioning.

The field sequence

Identify the metering device first. Fixed orifice: superheat is your charge check. TXV: the valve holds superheat steady — subcooling is the charge check.
Measure before you touch anything: suction and liquid line pressures and temperatures, converted with the refrigerant's pressure–temperature table.
Check airflow before the charge: filter, coil, blower. Starved airflow skews both numbers and sends technicians to the recovery machine for nothing.
Read the pair together. High superheat with high subcooling points at restriction, not charge. Low on both points at undercharge — after airflow is proven.
Only then adjust charge, in small increments, re-measuring each time. Work in the nameplate's units — °C and kelvin on most international equipment; the lab skin shows this region's readings.

Common wrong moves

Adding gas on a TXV system because superheat looks high.
Lab fail: on a TXV, high superheat usually means airflow or restriction — charging masks it and overcharges.
Hooking up gauges before looking at the filter and coil.
Lab fail: airflow not proven — every later reading is built on sand.
Applying memorised target numbers from one market to a nameplate in another unit system.
Lab fail: wrong-unit readings — use the regional nameplate values the lab shows.

Run it, don't just read it

The lab grades the same sequence you just read — isolation, measurement order, and the decision — with a debrief on every call.

Play the superheat/subcooling lab Start exam-prep path

After the labs, you know which exam to book

After the labs, you know which exam to book. Prep here for EPRA, NABCEP, EPA 608, NATE, CEC, SAQCC Gas and ESSCI, then book with that body when the labs are done.
EcoPowerHub Academy is the prep and issues its own completion record. The examining body is the issuer of the credential you sit for.
Work on photovoltaic, battery, and electrical systems involves potentially lethal voltages and must only be performed by qualified persons, in accordance with applicable codes, regulations, and employer safety programs.
Labs and materials are educational. The technician and their employer remain solely responsible for safe work practices, isolation, PPE, and compliance on actual jobs.
Exam and licence fees are paid to the examining body. Academy completion is training.

The field sequence

Common wrong moves

Run it, don't just read it

Keep going

After the labs, you know which exam to book