Nordic ATWC Series, Installation And Service Manual, Page: 63 / 106

PRELIMINARY: 24-Sep-2021 Page 63 002536MAN-00
OPERATION TROUBLESHOOTING - HEATING MODE
Fault Possible Cause Verification Recommended Action
Outdoor tempera-
ture reading is
incorrect by a
large amount
Outdoor EEV is mechani-
cally faulty and causing
electromagnetic interfer-
ence
Verify EEV operation (EEV3 or
EEV4) - see EEV Troubleshooting
section
Replace outdoor EEV if faulty.
Faulty outdoor tempera-
ture sensor or outdoor
MODBUS board
Outdoor EEV verified to be good, no
loose connections in indoor to out-
door control wiring
Replace outdoor temperature
sensor or outdoor MODBUS
board.
High or low suc-
tion or discharge
pressure
Faulty sensor Compare pressure sensor reading
against a known reference such as a
new refrigeration manifold set.
Check wiring, replace sensor. If
problem persists, replace con-
trol board.
High discharge
pressure:
Stage 1 - R410a or
Stage 2 - R134a
Low indoor loop flow rate Verify that indoor delta T is 8-12°F
(4-7°C)
Increase flow rate if new instal-
lation, check for fouled heat ex-
changer if existing installation.
Outdoor unit’s EEV3 or
EEV4 stuck almost closed
or partially blocked by for-
eign object
Manually adjusting the outdoor EEV
does not affect the superheat or the
suction pressure. High superheat,
low suction pressure.
Go to EEV troubleshooting sec-
tion.
Filter-dryer plugged Feel each end of the filter-dryer; they
should be the same temperature. If
there is a temperature difference then
it is plugged. Also causes low suc-
tion pressure.
Replace filter-dryer.
Unit is overcharged High subcooling, low Indoor Loop
delta T.
Remove 1/2 lb of refrigerant at
a time and verify that the dis-
charge pressure reduces.
Low suction
pressure:
Stage 1 - R410a or
Stage 2 - R134a
Indoor OUT temperature
too cold (on startup or if
unit has been off for ex-
tended period)
Ensure Indoor OUT temperature is
above the low limit indicated in the
Model Specific Information section.
Reduce flow temporarily until
Indoor Out temperature has
risen sufficiently.
Low or no outdoor unit
airflow
Visually check outdoor fan to see if it
is operating.
Go to Outdoor Fan Trouble-
shooting section.
TS1 or TS2 temperature
sensors not reading
properly
If the sensor is reading low it will
cause the superheat to appear high,
which causes the EEV to continually
close.
Verify EEV position is low com-
pared to normal. Check tem-
perature sensor, replace if nec-
essary.
Filter-dryer plugged Feel each end of the filter-dryer; they
should be the same temperature. If
there is a temperature difference then
it is plugged. Also causes high dis-
charge pressure.
Replace filter-dryer.
Outdoor unit’s EEV3 or
EEV4 stuck almost closed
or partially blocked by for-
eign object
Manually adjusting the outdoor EEV
does not affect the superheat or the
suction pressure. High superheat
and high discharge pressure.
Go to EEV troubleshooting sec-
tion.
Low refrigerant charge Superheat is high, outdoor EEV posi-
tion is high.
Locate the leak and repair it.
Spray Nine, a sniffer, and/or
dye are common methods of
locating a leak.