Nordic AH4P Series, Service Manual

Page: 17 / 30

5-Jul-2022 Page 17 002596MAN-01
POWER SUPPLY TROUBLESHOOTING
Fault Possible Cause Verification Recommended Action
No power to the
air handler
Disconnect switch open
(if installed)
Verify disconnect switch is in the
ON position.
Determine why the disconnect
switch was opened, if all is OK
close the switch.
Fuse blown /
breaker tripped
Breaker is tripped at panel; or at air
handler disconnect box, voltmeter
shows 230VAC on the line side but
not on the load side.
Reset breaker or replace fuse with
proper size and type. (Time-delay
type “D”)
No display on
thermostat.
Transformer impedance
protection has been acti-
vated due to a short cir-
cuit, or faulty transformer
230VAC is present across L1 and
L2 of the air handler power strip but
24VAC is not present across R and
C of the terminal strip.
Replace transformer.
Faulty wiring between air
handler and thermostat
24VAC is not present across R and
C of the thermostat.
Correct the wiring.
Faulty Thermostat 24VAC is present across R and C
of the thermostat but thermostat
has no display.
Replace thermostat.
STEP 1: If there is a thermostat powered from the air handler’s R and C terminals, verify that the display is present.
If it is not, proceed to POWER SUPPLY TROUBLESHOOTING; otherwise proceed to STEP 2.
STEP 2: If a 24VAC signal does not appear across G and C of the air handler’s terminal strip (or a DC signal across
0-10VDC+ and GND for –VSP models) within 6 minutes, proceed to the THERMOSTAT TROUBLESHOOT-
ING section; otherwise, proceed to the FAN/BLOWER TROUBLESHOOTING section.
Troubleshooting Guide
THERMOSTAT TROUBLESHOOTING
Fault Possible Cause Verification Recommended Action
Incorrect thermostat or
controller setup
Thermostat or controller does not
indicate a call for heating or cooling.
No output signal from thermostat or
controller.
Correct the setup.
Faulty thermostat or con-
troller to air handler wiring
Signal present at output of the ther-
mostat or controller but not present
across G and C (or 0-10VDC+ and
GND) of the air handler’s terminal
strip.
Correct or replace wiring.
Faulty thermostat or con-
troller
No output signal from thermostat or
controller when a demand is indicat-
ed.
Replace thermostat or controller.
No G signal to air
handler
(or 0-10VDC
signal for –VSP
models)