Trane ACONT900AC43UA Service Manual page 80

Refrigeration Cycle Problems
Step 2
The reversing valve 24 volt coil will become energized
and the valve will shift. If not, check for the presence of
24 volts at the coil (Figure 7).
Figure 7
Step 3
If voltage is present, shut the system down, discon-
nect power to the unit, remove one wire from the coil,
and perform an Ohms check on the coil (Figure 8).
An infinite reading will indicate an open coil. If the coil
is open, replace the coil, restore power, and check for
proper operation. If the ohms reading is good, recon-
nect the wire, restore power, and call for heat (Heat
pump mode).
Figure 8
HP - G 4
Step 4
Let the unit run for several minutes, then force a de-
frost cycle again. Place the metal end of a screw-
driver near the end of the reversing valve coil (Figure
9). Magnetic pull on the screwdriver will indicate that
the coil is working properly. The valve would then be
considered mechanically defective, replace the valve.
Figure 9
Step 5
If no voltage is present at the coil during a forced de-
frost cycle, check for 24 volts at the defrost control
board (Figure 10). If voltage is present at the defrost
control board, check for a defective wiring harness.
No voltage at the defrost control board indicates a de-
fective defrost control board. Replace the board.
Figure 10