Disconnect all power
sources from air handler
Using ohm meter, place
leads across A & B
heaters NTCO.
NOTE: If NTCO / Element open fault
occurs at power up and all NTCO and
elements indicate to be good, verify that
all heat relays are operating correctly.
See Fault Code #3 instructions
Troubleshooting Communicating EHC
Fault Code #4 – NTCO / Element Open
Are zero ohms
read across the
NTCO?
NTCO is good YES
Element(s) is open
Replace heater
assembly
Reset Fault History
and check operation
Verify all wiring
and connections
are correct.
YES
Replace NTCO
Check operation
NO
Is heating element(s)
resistance between 11-
13 ohms? See element
layout.
Elements are good
YES
NO
Heating Element Layout
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