Defrost Thermostats; Indoor Fan Off Delay; Defrost Speedup Functions - Carrier WeatherMaster 50HCQ04-12 Service And Maintenance Instructions

At the end of the continuous run period, the defrost control will
test for a need to defrost. On unit sizes 04-07 (single compres-
sor designs), DFT1 controls the start and termination of the de-
frost 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 peri-
od will end when DFT1 opens (indicating the outdoor coil has
been cleared of frost and ice) or a 10 minute elapsed period ex-
pires, whichever comes first.
ON UNIT SIZES 08 AND 12 (TWO CIRCUIT DESIGNS)
DFT2 (located on the bottom circuit of the outdoor coil on the
08-09 size and the outdoor coil with two bends on the 12 size)
controls the start and termination of the defrost cycle. If DFT2
is still open, the defrost test/run window is closed and the con-
trol 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 (indicating the outdoor coil has been
cleared of frost and ice) or a 10 minute elapsed period expires,
whichever comes first.
ON SIZES 08-12
Circuit 1's defrost thermostat DFT1 (located on the upper cir-
cuit of the outdoor coil on 08-09 size and the outdoor coil with
one bend on the 12 size) 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 cycle, Circuit 1 will also enter a defrost cycle.
Circuit 1's defrost cycle will end when DFT1 opens (indicating
the upper portion of the outdoor coil is cleared of frost and ice)
or the Circuit 2 defrost cycle 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 terminat-
ed, the defrost control will remember where the run period was
interrupted. On restart in Heating, the defrost control will re-
sume unit operation at the point in the run period where it was
last operating.
1 2
1
0 J J
90 Minutes
Table 9 — DIP Switch Positions
1 2
1 J 1
0 J 0
60 Minutes

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 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 position dis-
ables 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. 34); 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 De-
frost 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 Defrost cycle.
1 2 1
J 1 J
J 0
30 Minutes 120 Minutes
23
2 3
J 1
0 J
Fan Delay
On
Off