Staging; Compressor Clutch Control; Ram Air Control; Startup - Carrier 68G5-105 Series Operation & Service Manual

2.3.9 Staging

When the system is started, the fans are staged on to
reduce the total starting current. There is no staging
required for the driver evaporator fan motors, as they
start immediately. Staging for the evaporator and
condenser fan motors are given in the Table 2-2.
Table 2-2. Main area Staging
Time
Ref.
(seconds)
Time 0 0 Main Evaporator Fan Low
Time 2 Time 0 + 2 Main Evaporator Fan High
Time 3 Time 0 + 4 Condenser Fan 1 Low
Time 4 Time 3 + 1 Condenser Fan 2 Low
Time 5 Time 3 + 3 Both Condenser Fans High

2.3.10 Compressor Clutch Control

A belt driven electric clutch is employed to transmit en-
gine power to the air conditioning compressor. De-ener-
gizing the clutch electric coil disengages the clutch and
removes power from the compressor. The clutch will be
engaged whenever any area is calling for cooling. The
clutch will be disengaged when the system is off, when
all areas are in heating or during high and low pressure
conditions. The clutch coil is controlled by the main con-
troller.
The clutch coil is prevented from engagement when the
ambient temperature is below 32_F (0_C).
The clutch coil will be de-energized if the discharge
pressure rises to 350 psig (2.4 mPa), the setting of the
compressor mounted high pressure switch. The clutch
coil will energize when the discharge pressure falls to
240 psig (1.7 mPa).
The clutch coil will be de-energized if the suction press-
ure decreases below 6 psig (41 kPa).

2.3.11 RAM Air Control

The RAM air control regulates admission of outside air
into the system.
T-312
Controller Action
a. Display Override
The RAM air can be automatically controlled or set to
open or closed by the display.
b. RAM Air Auto Mode
1. If the passenger return air temperature is greater
than controller set point plus 2_F (1.1_C) or less than
set point minus 2_F (1.1_C), the RAM air will be
closed.
2. Otherwise, RAM air is open.
An exception to the above is that there is a five minute
delay to open RAM air once it is closed in the auto mode.
There is no delay to close RAM air.

2.3.12 Startup

At startup, the controller will power on and perform all
power up tests.

2.3.13 Input Processing

The system determines correct operation by reading
temperature sensors
transducers and the humidity sensor. Refer to section
1.5 for electrical specifications for input devices and
sections 1.2.1, 1.2.2 and 1.2.6 for functional
descriptions.

2.3.14 Self Tests

With the engine running, self tests are automatically
executed.
"ER5" indicates a data memory failure. "ER6" indicates
a program memory failure. If any of these or any other
errors are displayed on the screen, proceed to
Table 3-1.

2.3.15 Alarm Description

Alarm descriptions and troubleshooting procedures are
provided in section 3.

2.3.16 Hour Meters

An hour meter records the compressor run time in
hours. The maximum reading is 999,999.
An Hourmeter records the total elapsed time the
controller has been on in hours. The maximum reading
is 999,999.
2.3.17 Communications (Driver Display -
Controller)
The controller uses communications to transmit data to
the display. The communications link is RS232.
2-6
(thermistors), pressure