Trane 4TWR4036N - Compressor Start Troubleshooting; Outdoor TXV;Heating Mode Troubleshooting

20 18-BC95D1-5E-EN
Section 17. Troubleshooting
Is contactor
engergized?
(contacts closed)
Compressor fails to start
Contactor check
YES
YES
YES
YES
NO
NO
NO
NO
NO
If applicable, is TDR
input voltage
present
Go To: Compressor won’t run
Check for 24 volts AC
across contactor coil
Is voltage
present at
contactor coil?
Replace contactor
Check control
transformer and
control fuse
Is the control
transformer
and fuse good?
Jumper R to Y low
voltage terminals
at thermostat sub
base.
Does the
contactor
energize?
Replace the room
thermostat
Repair or replace
transformer or fuse.
Investigate cause for
failure (possible short in
field wiring)
Repair or replace
connecting wiring
NO
Check ID Low
voltage
transformer
YES
Wait 3 minutes and
check contactor
coil again
Measure sub-cooling at
the outdoor unit.
Is subcooling greater
than 8°?
NO
YES
Is outdoor
ambient above
55 °F?
Remove sensing bulb from the
suction line. Observe liquid
pressure and suction pressure while
holding the bulb in bare hand for
one minute.
Does Liquid pressure decrease and
suction pressure increase?
YES
Replace the
TXV
TXV is OK
Measure superheat on suction
line at TXV sensing bulb.
Is superheat over 6°F and
under 20°F?
NO
YES
Verify system charge
using Service Facts
Before starting, insure proper fan motor
operation and both indoor and outdoor
coils are clean and clear of ice.
Stop. Outdoor
ambient is too
warm for this
test
NO
YES
NO
Troubleshooting Outdoor TXV / Heating Mode