Pioneer YN020GMFI22M2D Service Manual page 48

Pic 1: Use a multimeter to test the
DC voltage between 2 (previously:
L2) port and S port of outdoor unit.
The red pin of multimeter connects
with 2 (previously: L2) port while
the black pin is for S port.
(Set the multimeter to read DC volts
When AC is normal running, the
voltage will move alternately
between positive value and
negative value.