Carrier 40GXC Service Manual page 18

DIAGNOSTIC CHARTS (CONT.)
Reset circuit breaker. Is Reset circuit breaker. Is
problem fixed? problem fixed?
No No
Check the wires (type) and Check the wires (type) and
connections between connections between
Indoor and outdoor units Indoor and outdoor units * *
Yes Yes
Reset main power and Reset main power and
restart system using remote. restart system using remote.
Problem persists? Problem persists?
Yes Yes
Measure Volts DC on Measure Volts DC on
outdoor TB between S & N. outdoor TB between S & N.
Ok? ** Ok? **
No No
Replace outdoor board. Replace outdoor board.
* Thermostat wires cannot be used. Wires should be connected
communication error. Polarity needs to be maintained between indoor and outdoor units
** There is 3 minutes to make the measurement before the diagnostic light comes back on.
Yes Yes
Problem fixed Problem fixed
Fix connection or Fix connection or
No No
replace wiring replace wiring
No further action is No further action is
No No
required required
Measure Volts DC on Measure Volts DC on
Yes Yes
indoor TB between S & N. indoor TB between S & N.
Ok? ** Ok? **
No No
Replace indoor board. Replace indoor board.
per connection diagrams. Failure to do that will result in a
Fig. 30 – Communication Error
Reset main power and Reset main power and
restart system using remote. restart system using remote.
Problem persists? Problem persists?
Yes Yes
Check sensor connector Check sensor connector
at ID or OD board at ID or OD board
Connection good? Connection good?
Yes Yes
Check input and output Check input and output
on indoor or outdoor board. on indoor or outdoor board.
Yes Yes
Check sensor resistance. Check sensor resistance.
Appendix A4 Appendix A4
Yes Yes
Double check connection, Double check connection,
for corrosion or high for corrosion or high
resistance. resistance.
Fig. 31 – Temperature Sensor
Notes: Notes:
Before measuring the Volts DC on outdoor TB, Before measuring the Volts DC on outdoor TB,
disconnect the field wire on terminal S. disconnect the field wire on terminal S.
Before measuring the Volts DC on Indoor TB, Before measuring the Volts DC on Indoor TB,
disconnect the field wire on terminal S. disconnect the field wire on terminal S.
Have the red probe of the meter on terminal S Have the red probe of the meter on terminal S
and the black probe on terminal N. Reconnect and the black probe on terminal N. Reconnect
wiring when measurements are complete. wiring when measurements are complete.
Recheck wiring and Recheck wiring and
Yes Yes
connections connections
No No
No further action is No further action is
required required
No No
Fix connection Fix connection
No No
Replace board Replace board
No No
Replace sensor Replace sensor
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