Trane ACONT900AC43UA Service Manual page 73

If the relay is closed, 0 volts should be present. If line
voltage is measured, the relay contacts are open and
the Sump Heater Relay is defective. Replace the Sump
Heater Relay.
If 0 volts is measured, the relay contacts are closed
and line voltage is being switched to the Sump Heaters.
Check the electrical connections to the heaters. If
the wiring between the Sump Heaters and the Sump
Heater Relay check out good, the heaters have failed.
Sump heater fails to turn OFF
during compressor operation
Step 1
Call for either heat or cool mode compressor operation.
Step 2
Check for 24 volts between Sump Heater Relay
terminals 1 and 3 (Figure 4). 0 volts should be
measured as the relay should be de energized. If 0
volts is measured, continue to Step 3.
Figure 4
If 24 volts is present, check for 24 volts at terminal T2
on the Integrated Control Board. If 24 volts is present,
replace the Integrated Control Board.
Sump Heater
Step 3
If 0 volts is measured between the Sump Heater Relay
terminals 1 and 3, measure the voltage potential
between Sump Heater Relay terminals 2 and 4 (Figure
5). Line voltage should be measured. If 0 volts is
measured, the relay contacts are stuck closed.
Replace the Sump Heater Relay.
Figure 5
HP - E 3