Main Controller Automatic Control Sequence - Carrier 68G5-105 Series Operation & Service Manual

COOLING MODE
HIGH SPEED MAIN EVAP FAN
COMPR FULLY LOADED (6 CYL)
COOLING MODE
COMPR FULLY LOADED (6 CYL)
COOLING MODE
LOW SPEED MAIN EVAP FAN
COMPR FULLY LOADED (6 CYL)
COOLING MODE
LOW SPEED MAIN EVAP FAN
COMPR SEMI-LOADED (4 CYL)
REHEAT MODE
HUMIDITY LESS THAN 49%
LOW SPEED MAIN EVAP FAN
COMPR UNLOADED (2 CYL)
OR
HUMIDITY CONTROL MODE
HUMIDITY GREATER TAN 50%
HIGH SPEED MAIN EVAP FAN
COMPR FULLY LOADED (6 CYL)
HEAT MODE
LOW SPEED MAIN EVAP FAN
COMPR FULLY UNLOADED
(CLUTCH DISENGAGED)
HEAT MODE
COMPR FULLY UNLOADED
(CLUTCH DISENGAGED)
HEAT MODE
HIGH SPEED MAIN EVAP FAN
COMPR FULLY UNLOADED
(CLUTCH DISENGAGED)
FALLING
TEMP.
For humidity control refer to 2.3.4
Figure 2-4. Main Controller Automatic Control
Sequence
b. Cooling/Reheat
Cooling and reheat require various combinations of
evaporator fan speeds and compressor unloading.
Cooling is accomplished by energizing the compressor
and condenser, opening the liquid solenoid valve and
T-312
EVAPORATOR
RETURN AIR TEMP
ABOVE SET POINT
_ _ _ _ F _ _ _ _ C)
8.5 (4.75
_ _ _ _ F ( _ _ _ _ C)
8 4.5
_ _ _ _ F ( _ _ _ _ C)
6.75 3.75
_ _ _ _ F ( _ _ _ _ C)
5.5 3.0
SET POINT
_F (
- - 3.5 - - 2.0 _C)
_ _ _ _ F ( _ _ _ _ C)
- - 8 - - 4.5
_ _ _ _ F ( _ _ _ _ C)
- - 8.5 - - 4.75
RISING
TEMP.
2-4
closing the heating valve. The compressor clutch and
condenser fan motors are energized as appropriate.
Reheat allows for both net cooling and net heating by
varying the time that the heat valve is open. The time is
automatically calculated by the controller and is based
on a 20 second period.
c. Heating
In the heat capacity state, the liquid solenoid valve is
closed to stop cooling and the compressor will shut
down. The heating capacity can then be varied by
adjusting the time the heat valve is open. The time is
automatically calculated by the controller and is based
on a 20 second period.
d. Driver Area Control
The Driver's A/C switch on the left side console is turned
on when cooling is desired in the driver area.
The driver area conditions are controlled by manually
adjusting the Defrost and Heat slide switches on the
dash board. These controls operate in conjunction with
the main coach controller. Temperature control is ac-
complished by regulating the flow of engine coolant
through the heating coil in the driver evaporator (with the
Heat slide switch) by controlling a normally open electric
solenoid valve. The volume of air flow directed about the
driver area is controlled (with the Defrost slide switch) by
the speed of the drivers evaporator fan motors.
The heating coil reheats the precooled air to maintain
the desired temperature at the set point. During heat-
ing, the driver area liquid solenoid valve is closed and
the heating valve is opened and closed for a percentage
of the heat valve period.
e. Passenger Area Control
The passenger area temperature is controlled by
maintaining the return air temperature as measured by
the return air sensors located at the rear of the coach in
the return air ducts. The return air sensors are averaged
together to provide input for the controller.
If cooling is required for the passenger area, the
compressor and condenser will start and the main liquid
line solenoid valve is opened and the heat valve is
closed.
During reheat, the main liquid solenoid valve is opened
and the heating valve is opened and closed for a
percentage of the heat valve period (20 seconds).
To enter the heat mode for the passenger area, the
controller must be calling the heat valve to be cycling at
51% or higher. If this condition is not met, the area
requiring heat is put into reheat. During heating, the
main evaporator liquid solenoid valve is closed and the
heating valve is opened and closed for a percentage of
the heat valve period (20 seconds). Once the heat mode
has been entered, the controller will not re--enter heat
until the heat valve has closed to less than 25%.