Service manual

4-6T-294-01
4.4.5 Heating Mode
The unit will heat only when the controller set point is
above --10_C(+14_F), or --5_C(+23_F) optionally, as
relay THis electronically locked out to prevent heating
when the controller set point is below -- 1 0 _C(+14_F),
or --5_C(+23_F) optionally.
If the air temperature decreases 0.5_C(0.9_F) below
controller set point, TH closes (see Figure 4-2) and the
system enters the heating mode which is designed to
raise the container air temperature. When TH closes,
power flows through TH contacts and the heat
termination thermostat to energize the heatercontactor
(HR). This i n turn energizes the heaters and heat light.
The evaporator fans continue to run to circulate air
throughout the container.
As the supply air decreases to the in-range tolerance
below set point, relay TI and the in-range light
de-energize (after a 15 minute time delay) and will
remain de-energized until the supply air increases to a
tolerance below set point.
(Refer to section 3.1.4, Code 30.)
When thetemperature rises to 0.2_C(0.4_F) belowset
point, TH opens (heating off) and the system again
enterstheholding zone.Thecompressorandcondenser
fan motor are not running as contactors CH and CF
remain de-energized. The evaporator fans continue to
run to circulate air throughout the container.
A safetyheat termination thermostat (HTT) attachedto
an evaporator coil support, set to open at 54.5_C
(130_F), will open the heating circuit if overheating
occurs.