Indoor Fan Off Delay; Defrost Speedup Functions; Electric Heaters - Carrier WeatherMaker 50TCQ 17-24 Series Service And Maintenance Instructions

1 2
1
1
  0
0
90 minutes
At the end of the continuous run period, the defrost control will
test for a need to defrost. On the single circuit compressor designs,
DFT1 controls the start and termination of the defrost cycle. If
DFT1 is still open, the defrost test/run window is closed and the
control repeats the continuous run period. If DFT1 is closed, the
defrost cycle is initiated. The defrost period will end when DFT1
opens (indicating the outdoor coil has been cleared of frost and
ice) or a 10 minute elapsed period expires, whichever comes first.
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 initi-
ated in Circuit 2. The defrost period will end when DFT2 opens
(indicating 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
can 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 cy-
cle, Circuit 1 will also enter a defrost cycle. Circuit 1's defrost cy-
cle will end when DFT1 opens (indicating the upper portion of the
outdoor coil is cleared of frost and ice) or the Circuit 2 defrost cy-
cle is terminated.
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
terminated, 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 tempera-
ture 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 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 delay fea-
ture. Setting SW3 in the OPEN position turns the Fan Off Delay
feature on; setting SW3 in the CLOSED position disables this fea-
ture. 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 jump-
er wires JMP17 and JMP18 together (see Fig. 30); use a straight-
edge screwdriver.
Shorting the jumpers for a period of 1 to 3 seconds reduces the de-
frost timer periods by a factor of 0.1 sec/minute. (For example, 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.
Table 9 — Dip Switch Position
1 2 1
 1 
 0
60 minutes 30 minutes
2 1
1 
 0
120 minutes
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 de-
frost 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 50TCQ units may be equipped with field-installed accesso-
ry electric heaters. The heaters are modular in design, with heat-
er frames holding open coil resistance wires strung through ce-
ramic insulators, line-break limit switches and a control contac-
tor. One or two heater modules may be used in a unit. See Fig. 33
for control connections.
Heater modules are installed in the heater section access panel lo-
cated just below the blower access panel. Heater modules slide
into the compartment on tracks along the bottom of the heater
opening. See Fig. 34-36.
Not all available heater modules may be used in every unit. Use
only those heater modules that are ETL listed for use in a specific
size unit. Refer to the label on the unit cabinet for the list of ap-
proved heaters. See Table 10.
Unit heaters are marked with heater model numbers. But heaters
are ordered as and shipped in cartons marked with a correspond-
ing heater sales package part number.
NOTE: The value in position 9 of the part number differs between
the sales package part number (value is 1) and a bare heater model
number (value is 0).
CTB
CONTL
BOARD
2
VIO
3
ORN
12
BRN
ORN
TB4
VIO
Field
Connections
Fig. 33 — Accessory Electric Heater Control
Connections
23
2 3
 1
0 
Fan Delay
VIO BRN
1 2 3
VIO BRN BRN
Elec Htr
VIO HR2 BRN
VIO HR1 BRN
HR1: On Heater 1 in Position #1
HR2: On Heater 2 in Position #2 (if installed)
On
Off