Table of Contents
Advertisement
DEFROST
The defrost control mode is a time/temperature sequence.
There are two time components: The continuous run period
and the test/defrost cycle period. The temperature compo-
nent is provided by the defrost thermostats (DFT1 and
DFT2) mounted on the outdoor coil.
The continuous run period is a fixed time period between
the end of the last defrost cycle (or start of the current Heat-
ing cycle) during which no defrost will be permitted. This pe-
riod can be set at 30, 60, 90 or 120 minutes by changing the
positions of DIP switches SW1 and SW2 (see Fig. 25 and
Table 13). The default run period is 60 minutes.
Fig. 25 — DIP Switch Settings — Defrost Board
At the end of the continuous run period, the defrost control
will test for a need to defrost. DFT2 (located on the bottom
circuit of the outdoor coil) controls the start and termination
of the defrost cycle. If DFT2 is still open, the defrost test/run
window is closed and the control repeats the continuous run
period. If DFT2 is closed, the defrost cycle is initiated in
Circuit 2. The defrost period will end when DFT2 opens (in-
dicating the outdoor coil has been cleared of frost and ice)
or a 10 minute elapsed period expires, whichever comes
first.
Circuit 1's defrost thermostat DFT1 (located on the upper
circuit of the outdoor coil) cannot initiate a unit defrost cycle;
only DFT2 may do this. But once Circuit 2 is in defrost, the
DFB will monitor the status of DFT1. If DFT1 closes during a
Circuit 2 defrost cycle, Circuit 1 will also enter a defrost cy-
cle. Circuit 1's defrost cycle will end when DFT1 opens (indi-
cating the upper portion of the outdoor coil is cleared of frost
and ice) or the Circuit 2 defrost cycle is terminated.
1
2
1
•
0
•
30 minutes
CHS-180-240-01SI Rev. A
Table 13 — Dip Switch Position
1
2
1
•
1
0
•
0
60 minutes
Specifications subject to change without notice.
At the end of the unit defrost cycle, the unit will be returned
to Heating cycle for a full continuous run period. If the space
heating load is satisfied and compressor operation is termi-
nated, the defrost control will remember where the run peri-
od was interrupted. On restart in Heating, the defrost control
will resume unit operation at the point in the run period
where it was last operating.
DEFROST THERMOSTATS
These are temperature switches that monitor the surface
temperature of the outdoor coil circuits. These switches are
mounted on the liquid tube exiting the outdoor coil heating
circuits. These switches close on temperature drop at 30°F
(–1°C) and reset open on temperature rise at 80°F (27°C).
INDOOR FAN OFF DELAY
The DFB can provide a 30 sec delay on Indoor Fan Off if the
thermostat's fan selector switch is set on AUTO control.
DIP Switch SW3 on the DFB selects use of the fan off time
delay feature. Setting SW3 in the OPEN position turns the
Fan Off Delay feature on; setting SW3 in the CLOSED posi-
tion disables this feature. The delay period begins when Y1
demand or W1 demand by the space thermostat is
removed.
DEFROST SPEEDUP FUNCTIONS
The DFB permits the servicer to speed-up the defrost cycle.
There are two speed-up sequences: relative speed-up and
an immediate forced defrost. Speed-up sequences are initi-
ated by shorting jumper wires JMP17 and JMP18 together
(see Fig. 23); use a straight-edge screwdriver.
Shorting the jumpers for a period of 1 to 3 secs reduces the
defrost timer periods by a factor of 0.1 sec/minute. (For ex-
ample, the 90 min run period is reduced to 9 secs.) The
DFB will step the unit through a Heating cycle and a Defrost
cycle using these reduced time periods. This mode ends af-
ter the Defrost cycle.
Shorting the jumpers for a period of 5 to 20 secs bypasses
the remaining continuous run period and places the unit in a
Forced Defrost mode. If the controlling DFT is closed when
this mode is initiated, the unit will complete a normal defrost
period that will terminate when the controlling DFT opens or
the 10 minute defrost cycle limit is reached. If the controlling
DFT is open when this mode is initiated, the Defrost cycle
will run for 30 secs. Both modes end at the end of the De-
frost cycle.
SWITCH NO.
1
2
1
1
•
•
0
90 minutes
1
2
3
•
•
1
0
•
Fan
120 minutes
Delay
On
Off
27
Advertisement
Table of Contents
