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: Service Manual
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13
A220833
Fig. 16 – DFT Sensor Location 060
Troubleshooting
If unit will not run:
1. Does the Y input has 24 volts from thermostat? If not, check
thermostat or wire. If yes proceed to #2
2. The Y spade terminal on the circuit board should have 24 volts if Y
input is energized. This output goes through the pressure switches
and to the contactor. If 24 volts is present on the Y spade terminal,
and the contactor is not closed, check voltage on contactor coil. If
no voltage is present, check for opened pressure switch.
3. If voltage is present and contactor is open, contactor may be
defective. Replace contactor if necessary.
4. If contactor is closed and unit will still not run, check wiring,
capacitor and compressor.
Defrost Speedup
To test the defrost function on these units, speed up pins are provided on
the circuit board. To force a defrost cycle, the defrost thermostat must be
closed, or the defrost thermostat pins must be jumpered. Follow the steps
below to force a defrost cycle:
1. Jumper the DFT input .
2. Short the speed up pins. This speeds up the defrost timer by a factor
of 256. The longer the defrost interval setting, the longer the pins
must be shorted to speed through the timing. For example, if
interval is 90 min, the speed up will take (90/256) min x (60
seconds /minute) = 21 seconds max. This could be shorter
depending on how much time has elapsed since the defrost
thermostat closed.
3. Remove the short immediately when the unit shifts into defrost.
Failure to remove the short immediately will result in a very short
forced defrost cycle (the 10 minute timer will be sped through in 2
seconds).
4. When defrost begins, it will continue until the defrost thermostat
opens or 10 minutes has elapsed.
NOTE:
The T1 terminal on the defrost board powers the defrost timing
function. This terminal must be energized before any defrost function
will occur.
If defrost thermostat is stuck closed:
Whether the unit is in heating or cooling mode, it will run a defrost cycle
for 10 minutes each time the compressor has been energized for the
selected time interval. The board will terminate automatically after 10
minutes of defrost time regardless of defrost thermostat position.
If defrost thermostat is stuck open:
The unit will not defrost
If unit will not defrost:
1. Perform the speedup function as described above to test the defrost
function of the circuit board.
2. If the unit does not go into defrost after performing the speed up,
check for 24 volts on the T1 terminal. This terminal powers the
defrost circuit, and must be energized before any defrost function
can occur. The T1 should be energized once the Y terminal is
energized and the pressure switches are closed. Ensure the T1 wire
is connected at the contactor, and that 24 volts is present on the T1
terminal.
3. If all voltages are present and unit will still not run defrost, remove
thermostat pigtail harness from board and perform checks directly
on input pins with jumper wires. The pigtail may have a bad
connection or be mis-wired.
To fully troubleshoot defrost thermostat and control function :
1. Turn thermostat to OFF. Shut off all power to outdoor unit.
2. Remove control box cover for access to electrical components and
defrost control board.
3. Disconnect defrost thermostat leads from control board, and
connect to ohmmeter. Thermostat leads are black, insulated wires
connected to DFT and R terminals on control board. Resistance
reading may be zero (indicating closed defrost thermostat), or
infinity (¥ for open thermostat) depending on outdoor temperature.
4. Jumper between DFT and R terminals on control board as shown in
5. Disconnect outdoor fan motor lead from OF2. Tape lead to prevent
grounding.
6. Turn on power to outdoor unit.
7. Restart unit in heating mode, allowing frost to accumulate on
outdoor coil.
8. After a few minutes in heating mode, liquid line temperature at
defrost thermostat should drop below closing set point of defrost
thermostat of approximately 32°F (0ºC). Check resistance across
2. Defrost switch can either be located on the bottom of tube
(as shown) or on the top and must not interfere with any other
tubing.
060 13.4 SEER2