Trane ACONT900AC43UA Service Manual page 79

Step 2
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 3). 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 cooling.
Figure 3
Step 3
Place the metal end of a screwdriver near the end of
the reversing valve coil (Figure 4). Magnetic pull on the
screwdriver will indicate that the coil is working prop-
erly. The valve would then be considered as having
failed, replace the valve.
Figure 4
Refrigeration Cycle Problems
Step 4
If no voltage is present at the coil during a call for
cooling, check for 24 volts at the defrost control board
(Figure 5). If voltage is present at the defrost control
board, check for a defective wiring harness. No volt-
age at the defrost control board indicates a defective
defrost control board or thermostat/wiring.
Figure 5
HEATING MODE
When operating in the heat pump mode, and the out-
door unit exhibits severe frosting, it is possible the
defrost cycle is not being performed. To check this
function, a forced defrost cycle will need to be initi-
ated.
Step 1
With the unit operating, use a screwdriver and short
between the TEST_COMMON pin and the FRC_DFT
pin on the defrost control board. (Hold the screwdriver
in place for at least 2 seconds.)(Figure 6.)
Figure 6
HP - G 3