Carrier 38GXC - Manual (Page 14)

14
Heating Mode
In this mode, the system heats the room air with the indoor fan
running at either the selected speed or on Auto. As the cooling
mode, the indoor fan will run continuously unless interrupted by
the cold blow algorithm. This algorithm will not allow the fan to
run if the indoor coil temperature drops below a preset value.
Compressor and fan operation
As shown below, the compressor and outdoor fan cycle on and off
based on the actual room temperature versus the set point. The
outdoor fan is de--energized 30 seconds after the compressor is
de--energized. The reversing valve is energized in heating and will
stay energized for 2 minutes after the compressor is de--energized.
The reversing valve is energized 2 seconds before the compressor
is energized.
Compressor
Outdoor Fan
Indoor Fan
Reversing Valve
T
S
+ 3.6°F
T
S
+ 9°F
T
S
+ 9°F
T
S
+ 3.6°F
30 S
≥ 3 minutes
2 S
Compressor
matches load
Cold Blow
prevention
2 minutes
A09252
Fig. 20 – Heat Mode
Indoor Fan Operation – Heating
When in heating mode, as long as the coil temperature is above the
threshold for cold blow prevention, the fan runs continuously
either at the chosen set speed, or in Auto mode, where the speed is
determined by the microprocessor based on the difference between
the room temperature and the temperature set point as shown
below:
T
S
+ 5.4°F
Medium
Low
High
T
S
+ 1.8°F
A09254
Fig. 21 – Auto Fan -- Heat Mode
Cold Blow Prevention
This function prevents the cold air from blowing into a space when
in heat mode. When there is a demand for heating one of the
following conditions occurs:
S If the indoor coil temperature is < 106_F (41.1_C) and
the room temperature is < 75_F (23.4_C), there will be a
3 minute time delay before the indoor fan runs at low
speed for 5 minutes.
S If the indoor coil temperature is ≥106_F (41.1_C) and
the room temperature is ≥75_F (23.4_C, the indoor fan
will run at low speed for 1 minute.
After one of the above steps occur, the indoor fan speed will be
determined as shown below:
Low
Medium
High
User selected
100.4 °F 109.4 °F
A09354
Fig. 22 – Cold Blow Prevention
Defrost
Defrost is controlled by the microprocessor and will occur if the
unit operated in the heating mode for at least 45 minutes and any of
the conditions below lasted for more than 3 minutes.
32 23 41 °F
Outdoor Temperature
10.4
14
21.2
28.4
Coi
l T
e
mperature
32 23 41 °F
A09355
Fig. 23 – Defrost
The defrost cycle will terminate 12 minutes after the initiation of
the defrost cycle or when the coil temperature is ≥50_F (10_C).
The defrost algorithm is shown below:
Defrost Initiated Defrost Terminated
Indoor Fan
Outdoor Fan
Reversing Valve
Compressor
75 S
12 min or tube
temp ≥ 50°F
25 Hz
Cold Blow
Prevention
A09256
Fig. 24 – Defrost (continued)
38/
40GX
C
(Q
)