8
SERVICING
When servicing, it may be necessary to rapidly advance
the system through a defrost cycle. To do this:
WARNING
To avoid electrical shock or death,
disconnect the electrical power.
1. If the outdoor coil temperature is above 30°F, place
a jumper wire from R on the low voltage terminal strip
to 24V on the defrost control.
2. Place a jumper wire from TST to TST on the defrost
control.
3. Reconnect the electrical power.
4. Place the system into heating operation.
5. The defrost cycle is now 256 times faster than normal:
90 minute run time now equals 21 seconds, 1
0
minute defrost time now equals 2 to 3 seconds.
6. After servicing is completed, disconnect the power,
then remove R-24V and TST-TST jumper wires, re-
place panels, reconnect the power.
DEMAND DEFROST CONTROL
Defrosting of the outdoor coil is determined by both coil
temperature and the length of the last defrost cycle. The
compressor run time between defrost periods is automati-
cally adjusted with every defrost cycle (minimum of 30
minutes and maximum of 360 minutes).
WARNING
To avoid electrical shock or death,
disconnect the electrical power.
When servicing, it may be necessary to rapidly advance
the system through a defrost cycle. To do this:
1. If the outdoor coil temperature is above 30°F, place
a jumper wire from R on the low voltage terminal strip
to one of the sensor (SEN) pins on the defrost control
board.
2. Place a jumper wire from TST to COM on the defrost
control board.
3. Reconnect the electrical power.
4. Place the system into heating operation.
NOTE: The HOLD (HLD) terminal must also be energized
by 24VAC to indicate compressor operation.
5. The defrost cycle is now 180 times faster than normal:
360 minute run time now equals 2 minutes, 30 minute
run time now equals 10 seconds, 10.5 minute maxi-
mum defrost time now equals 3 to 4 seconds.
6. After servicing is completed, disconnect the power,
then remove R-24V and TST-COM jumper wires,
replace panels, reconnect the power. The next pro-
grammed run time will be 30 minutes, if defrost is
terminated during the jumper test.
Figure 6
