Carrier WeatherMaker 50KCQ A04 Series Installation Instructions Manual page 24

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 terminat-
ed, the defrost control will remember where the run period 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 tem-
perature of the outdoor coil circuits. These switches are mount-
ed 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 60 second 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 de-
lay feature. Setting SW3 in the OPEN position turns the Fan
Off Delay feature on; setting SW3 in the CLOSED position
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 initiated by
shorting jumper wires JMP17 and JMP18 together (see
Fig. 36); use a flat-blade screwdriver.
Shorting the jumpers for a period of 1 to 3 seconds reduces the
defrost timer periods by a factor of 0.1 sec/minute. (For exam-
ple, the 90 minute run period is reduced to 9 seconds.) The
DFB will step the unit through a Heating cycle and a Defrost
cycle using these reduced time periods. This mode ends after
the Defrost cycle.
Shorting the jumpers for a period of 5 to 20 seconds 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 seconds. Both modes end at the end of the Defrost
cycle.
Electric Heaters
The 50KCQ units may be equipped with field-installed acces-
sory electric heaters. The heaters are modular in design, with
heater frames holding open coil resistance wires strung through
ceramic insulators, line-break limit switches and a control con-
tactor. One or two heater modules may be used in a unit.
Heater modules are installed in the compartment below the in-
door (supply) fan outlet. Access is through the indoor access
panel. Heater modules slide into the compartment on tracks
along the bottom of the heater opening. See Fig. 39-41.
Not all available heater modules may be used in every unit.
Use only those heater modules that are UL listed for use in a
specific size unit. Refer to the label on the unit cabinet for the
list of approved heaters.
DISCONNECT MOUNTING
LOCATION
UNIT BLOCK-OFF
PANEL
Fig. 39 — Typical Access Panel Location (3-5 Ton)
DISCONNECT EMT OR RIGID CONDUIT
MOUNTING (FIELD-SUPPLIED)
LOCATION
SINGLE POINT
MAIN BRACKET AND BOX
CONTROL CONDUIT MOUNTING
BOX DRIP BOOT SCREW
CONTROL WIRE TERMINAL BLOCK
Fig. 40 — Typical Component Location
Fig. 41 — Typical Module Installation
24
INDOOR
OUTDOOR
ACCESS
ACCESS PANEL PANEL
SINGLE CENTER MANUAL RESET
POINT BOX POST LIMIT SWITCH
HEATER
COVERS
HEATER HEATER HEATER
MODULE MODULE MOUNTING
(LOCATION 1) (LOCATION 2) BRACKET
TRACK
FLANGE