Carrier CH16NA Installation Instructions Manual page 7

Defrost
The defrost control is a time/temperature control which includes a
field selectable (quick–connects located at board edge) time period
between defrost cycles (30, 60, or 90 minutes), factory set to either
60 or 90 minutes.
The electronic defrost timer sequence is enabled when the T1 input
on the board is energized. The timer starts only when the defrost
thermostat is closed and the contactor is energized.
Defrost mode is identical to cooling mode except that outdoor fan
motor stops and second–stage heat is turned on to continue
warming conditioned spaces.
To initiate defrost, the defrost thermostat must be closed. This can
be accomplished as follows:
1. Turn off power to outdoor unit.
2. Disconnect outdoor fan motor lead from OF2 on control
board for units using PSC motors and from ODF terminal
on units with ECM motor (see Fig. 12). Tape lead to pre-
vent grounding.
3. Restart unit in heating mode, allowing frost to accumulate
on outdoor coil.
Fig. 11 – Defrost Control HK32EA001 for Units with PSC
Motors
PARAMETER
30–minute cycle
50–minute cycle
90–minute cycle
10–minute cycle
5 minutes
A05332
Table 3 – Defrost Control Speedup–Timing Sequence
MINIMUM
(MINUTES)
27
45
81
9
4.5
4. After a few minutes in heating mode, liquid line temperat-
ure should drop below closing point of defrost thermostat
(approximately 30°F/–1.11°C).
5. Short between speedup terminals with a flat–blade screw-
driver. This reduces the timing sequence to 1/25th of origin-
al time. (See Table 3.)
6. When you hear reversing valve change position, remove
screwdriver immediately; otherwise, control will terminate
normal 10–minute defrost cycle in approximately 2
seconds.
NOTE: Length of defrost cycle is dependent upon length of time
it takes to remove screwdriver from test pins after reversing valve
has shifted.
7. Unit will remain in defrost for remainder of defrost cycle
time or until defrost thermostat reopens at approximately
65°F (18.33°C) coil temperature of liquid line.
8. Turn off power to outdoor unit and reconnect fan motor
lead to OF2 on control board for units using PSC motors
and to ODF terminal on units with ECM motor.
Fig. 12 – Defrost Control HK32EA009 for units with ECM
Motor
MAXIMUM
(MINUTES)
33
55
99
11
5.5
7
A170138
SPEEDUP
(NOMINAL)
7 sec
12 sec
21 sec
2 sec
1 sec