Installer’s Guide
f. defroSt controL
(HEAT PUMPS ONLY)
The demand defrost control measures heat pump outdoor ambi-
ent temperature with a sensor located outside the outdoor coil. A
second sensor located on the outdoor coil is used to measure the
coil temperature. The difference between the ambient and the
colder coil temperature is the difference or delta-T measurement.
This delta-T measurement is representative of the operating state
and relative capacity of the heat pump system. By measuring the
change in delta-T, we can determine the need for defrost. The coil
sensor also serves to sense outdoor coil temperature for termina-
tion of the defrost cycle.
faULt IdentIfIcatIon
A fault condition is indicated by the fault LED on the control board
inside the heat pump control box.
In normal operation, the status LED will flash once each second. If
the light is flashing more than once per second or not at all, refer to
the Service Facts for that unit.
PIn IdentIfIcatIon
(SEE FIGuRE 6.)
1. TEST_COMMON (Shorting any of the other pins to this pin
causes the function of the other pin to be executed. Leaving
this pin open results in the normal mode of operation.)
2. TST = Test (Shorting TEST_COMMON to this pin speeds up
all defrost board timings.)
3. FRC_DFT = Forced Defrost (Short TEST_COMMON to this
pin for two [2] seconds to initiate a forced defrost. Remove the
short after defrost initiates.)
defroSt controL checkoUt
Normal operation requires:
a. Status LED on board flashing 1 time/second.
b. 12VDC between D & B.
c. Defrost initiation when FRC_DFT pin is shorted to TEST_
COMMON pin.
If a defrost control problem is suspected, refer to the service infor-
mation in control box.
frc_dft
teSt_coMMon
tSt
6
oUtdoor controL
Board – PIn
IdentIfIcatIon
G. coMPreSSor Start UP
After all electrical wiring is complete, SET THE COM-
FORTLINK™ II CONTROL SWITCH IN THE OFF POSITION SO
COMPRESSOR WILL NOT RUN, and apply power by closing the
system main disconnect switch. This will activate the compressor
sump heat (where used). Do not change the ComfortLink™ II con-
trol Switch until power has been applied for one (1) hour. Following
this procedure will prevent potential compressor overload trip at
the initial start-up.
4
18-BC53D2-3
