Carrier 25HCC5 Installation Instructions Manual page 7

Once defrost termination conditions have been met, the following
sequence will occur: The compressor will be de- -energized for
approximately 1 minute, then the reversing valve will be
de- -energized. A few seconds later, the compressor will be
re- -energized and the normal heating cycle starts.
Defrost
The defrost control is a time/temperature control which has field
selectable settings of 30, 60, 90, or 120 minutes, factory set to 90
minutes. These settings represent the amount of time that must pass
after closure of the defrost thermostat before the defrost sequence
begins.
The defrost thermostat senses coil temperature throughout the
heating cycle. When the coil temperature reaches the defrost
thermostat setting of approximately 32 _F (0 _C), it will close,
which energizes the DFT terminal and begins the defrost timing
sequence. When the DFT has been energized for the selected time,
OF2
DFT
T1
T2 C C O
O R W Y C
2
Fig. 11 – Defrost Control HK32EA008
PARAMETER
30–minute cycle
50–minute cycle
90–minute cycle
10–minute cycle
5 minutes
ON
120
30 60
QUIET
SHIFT
60 30
90
INTERVAL TIMER OFF
P3
Y
P1 DFT
J1
SPEEDUP
A05378
Table 4 – Defrost Control Speedup–Timing Sequence
MINIMUM
(MINUTES)
27
45
81
9
4.5
the defrost cycle begins. Defrost cycle is terminated when defrost
thermostat opens, or automatically after 10 minutes.
Defrost Speedup
To initiate a forced defrost, speedup pins (J1) must be shorted with
a flat head screwdriver for 5 seconds and RELEASED. If the
defrost thermostat is open, a short defrost cycle will be observed
(actual length depends on Quiet Shift- -2 switch position). When
Quiet Shift- -2 is off, only a short 30 second defrost cycle is
observed. With Quiet Shift- -2 ON, the speedup sequence is
approximately 3 minutes; 1 minute compressor off period followed
by 30 seconds of defrost with compressor operation. When
returning to heating mode, the compressor will turn off for an
additional 1 minute.
If the defrost thermostat is closed, a complete defrost cycle is
initiated. If the Quiet Shift- -2 switch is turned on, the compressor
will be turned off for two 1 minute intervals as explained
previously.
Fig. 12 – Defrost Control HK32EA010
MAXIMUM
(MINUTES)
33
55
99
11
5.5
7
A170130
SPEEDUP
(NOMINAL)
7 sec
12 sec
21 sec
2 sec
1 sec