AirComm Corporation Cessna Citation 550 560 Maintenance Manual
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Products, Inc.
Maintenance Manual
21-50-00
May 15/95 Page 1
AIR CONDITIONING SYSTEM - SYSTEM DESCRIPTION
1. GENERAL
The air conditioning system for the Cessna 500 series aircraft consists of a refrigerant
R134a vapor cycle cooling system. This system allows the co-pilot to control cooling
for a comfortable aircraft cabin. Figure 1 shows a general arrangement of the air
conditioning system.
The co-pilots control panel contains the cooling system ON/OFF/FAN switch, the
FWD fan LOW/HIGH switch, the AFT fan OFF/LOW/HIGH and a blue A/C system ON
indicator.
2. COOLING SYSTEM
The cooling or air conditioning system, as designed and manufactured by Keith
Products for the Cessna 500 Series aircraft, is a vapor cycle type cooling system
using refrigerant R134a. The system is electrically operated using the aircraft 28 VDC
electrical system and is operable in all normal flight modes up to 18,000 feet MSL. Air
conditioning may be operated with ground external power or the aircraft electrical
system providing 28 vDC to the non-essential buss.
The major components of the system are the compressor/condenser assembly with
blower, and two evaporator/cabin blower units. Refrigerant plumbing and electrical
systems connect the major component to provide a closed loop system.
The compressor/condenser assembly is mounted either forward of the rear baggage
door; or in the baggage compartment. The compressor drive and condenser fan drive
are both driven by a common, double shafted motor which turns at approximately
4500 RPM. The compressor is belt driven from the shortest shaft while the condenser
fan is attached directly to the longer motor shaft. Condenser cooling air (ambient air)
is drawn in through a cutout in either underside of the engine pylon or the right side of
the fuselage of the aircraft by the condenser fan. The air passes over the compressor
and drive motor to provide cooling airflow for those components prior to passing
through the condenser coil to remove heat from the system. After passing through the
condenser coil, the air is exhausted to the outside through an exhaust duct located
either on the underside of the fuselage; or through a cutout on the left side of the
aircraft. The compressor takes low pressure refrigerant gas and compresses it to a
higher pressure and temperature.
Products, Inc.
Maintenance Manual
21-50-00
May 15/95 Page 2
An evaporator/blower unit is located in the aft cabin at the end of the recessed isle
(at floor level) within the aircraft interior. It provides cooling airflow for the cabin
area of the interior. A forward evaporator is located at the cockpit floor and
provides cooling airflow to the flight crew through a floor mounted air outlet or
through dedicated ducting at the pilots and co- pilots control stick. Both
evaporators are of a design wherein the cabin air is drawn into the evaporator coil
and the fan then delivers the conditioned air to the cabin. This recirculating system
continues to dry and cool the air each time it passes through the evaporator.
Moisture removed from the air by the cold coil (condensate) is collected within the
evaporator housing and is forced overboard. Each evaporator is equipped with a
thermal expansion valve which regulates the amount of refrigerant entering the coil
to provide optimum cooling effect. The evaporator blowers can be operated in the
FAN position to re-irculate cabin air without cooling. Each blower is operated from
an independent fan speed control.
The plumbing which connects the compressor, condenser and the evaporators,
consists of rubber based hoses with a nylon barrier. The fittings are permanently
swaged onto the hoses. All fittings are o-ring type connections with sealant on the
fitting mating surfaces to prevent refrigerant leaks. Two R134a service valves are
located near the compressor/condenser pallet assembly. They are sized differently
to avoid incorrect cross-connecting when gaining access to the plumbing for system
recharging.
On the ground, the electrical system allows operation of the air conditioning system
from either aircraft power or from an active GPU prior to engine start. System safety
features include electrical interlocking and load shedding. In flight, the air
conditioning system can be operated from the aircraft electrical system only with
both generators on line. Loss of either generator will automatically shed the air
conditioning system electrical loads except for the minimal loads of the evaporator
fans.
The entire air conditioning refrigerant loop is protected against over pressure
conditions by two separate safety devices. The first device is a binary high/low
pressure switch that activates in the event of an overpressure and is on the
compressor discharge port. This switch will open at approximately 350 PSIG and
will interrupt power to the compressor control circuit. This in turn will de-energize
the compressor motor relay and remove power to the compressor motor. The
refrigerant system pressures will then drop. The switch will also interrupt power to
the compressor control circuit under low pressure conditions. The second
overpressure safety device is a fuse plug which will vent the system refrigerant
safely overboard in the event of a system pressure in excess of 425 PSIG. It is
located on the receiver/drier.
Products, Inc.
Maintenance Manual
21-50-00
May 15/95 Page 3
Figure 1. Air Conditioning System General Arrangement
Products, Inc.
Maintenance Manual
21-50-01
May 15/95
Page 1
ELECTRICAL
DESCRIPTION AND OPERATION
1. GENERAL
The air conditioning system consists of one high energy compressor/condenser
drive motor and two centrifugal evaporator blowers (Fwd) and (Aft). The system is
controlled by a mode switch with Air Conditioning Off and Fan Only position. Each
evaporator has a high and low position switch. A blue indicator light will illuminate
whenever the compressor/condenser is selected. The system incorporates a binary
pressure switch to sense an over pressure or under pressure condition in the
system.
The air conditioning system in controlled by a Logic Card which monitors generator,
GPU and battery inputs to ensure operation or shedding of the system if a fault
exists.
The system is protected by a 15 amp control and blower breaker and a 100 amp
breaker for the compressor/condenser drive motor.
This section of the maintenance manual describes the electrical system and
presents electrical troubleshooting procedures. An Illustrated Parts List is included
in Figure 1.
2. LOAD/SHED DESCRIPTION
The system incorporates a logic control PC card that enables the system to operate
or be shed under various conditions. The table below shows operation under
various conditions.
CONDITIONS
EVAP FANS COMP/COND
Gnd Power Cart/On On On
Gnd Power Cart Connected/Off On Off
Battery Only On Off
One Generator on Ground On On
Both Generators on Ground On On
Refrigerant Over/Under Pressure On Off
One Generator in Flight On Off
Both Generators in Flight On On
Products, Inc.
Maintenance Manual
21-50-01
May 15-95
Page 101
TROUBLESHOOTING
1. GENERAL
The following procedures are used for troubleshooting the electrical system and the
electrical interfaces with the other assemblies of the air conditioning system.
2. TOOLS AND EQUIPMENT
Designation
Ref. No.
Qty
Remarks
Service Pressure Gauge
Comm. Avail.
1
None
Multi-meter
Comm. Avail.
1
None
28vdc Source
A/R
None
3. ELECTRICAL TROUBLESHOOTING PROCEDURES (REF. IPL Fig. 1)
NOTE: Always attach a service gauge set to system prior to beginning trouble
shooting to insure proper refrigerant charge is present.
A. Air Condition Selected, Compressor/Condenser Motor Does Not Turn.
1. Connect service pressure gauge to service ports located near
compressor/condenser pallet.
2. Connect ground power to aircraft.
3. Select air conditioning system to ON.
4. Check that load shed start conditions in the Description and Operation
paragraph are met.
5. Check for power at comp/cond relay located on the pallet assembly, if not
present check 100A circuit breaker (4). Replace if necessary.
6. Check continuity of pressure switch (Ref. 21-50-03 IPL Fig. 1, item 11). If
no continuity and gauge set reads adequate pressure, replace pressure
switch. Switch can be removed without discharge of refrigeration. Back
switch off in a counter clockwise direction. Re-install in reverse order.
Lubricate o-ring in switch per 21-50-02 page 202.
Products, Inc.
Maintenance Manual
21-50-01
May 15/95
Page 102
7. Check for power at motor . If power is present, proceed to step 8. If
power is not present on either pin and load/shed conditions of step 4 are
met, check power on the load shed unit at connector Pin 1. If power is
present, system problem exists in load shed system start unit. If power is
not present, check 15 amp CB (3) and mode switch (26).
8. Fault is isolated to compressor/condenser motor. Unit should be
replaced.
9. Select air conditioning OFF, remove electrical power, disconnect service
gauge when troubleshooting is complete.
B. FWD Evaporator Blower will not operate in high or low speed.
1. Connect ground power to aircraft.
2. Select air conditioning system to ON.
3. Check if power and ground present at fan wire splices and GND terminal
strip. If power and ground are present, blower motor (Ref. 21-50-04 IPL
Fig.1, item 15, or IPL Fig. 2, item 24) has failed.
4. Select air conditioning OFF, remove electrical power.
5. Remove blower assy from aircraft. Remove the four screws attaching the
motor to the housing. Using a 1/8 allen wrench remove blower wheel
(use extreme care not to bend blower wheel). Cut power wires at splice
and remove Gnd wire from GND terminal. Install new motor in reverse
order.
C. FWD Evaporator Blower will not operate in the low speed setting.
1. Connect ground power to aircraft.
2. Select air conditioning system to ON.
3. Check if power is present at wire EVAP-FL (at splice). If power is
present, the low speed resistor (Ref. 21-50-04 IPL Fig. 1, item 17, or IPL
Fig. 2, item 23) has failed.
4. Select air conditioning OFF, remove electrical power.
5. Remove blower assembly and using a #21 drill remove the two rivets
securing the resistor. Cut the wires at the splice and remove GND wire
from GND terminal. Install new resistor in reverse order.
D. AFT Evaporator Blower will not operate in high or low speed.
1. Connect ground power to aircraft.
2. Select air conditioning system to ON.
3. Check if power and ground present at fan wire splices and GND terminal
strip. If power and ground are present, blower motor (Ref. 21-50-05 IPL
Fig.1, item 15) has failed.
4. Select air conditioning OFF, remove electrical power.
Products, Inc.
Maintenance Manual
20-50-01
May 15/95
Page 103
5. Remove blower assy from aircraft. Remove the four screws attaching the
motor to the housing. Using a 1/8 allen wrench remove blower wheel (use
extreme care not to bend blower wheel). Cut power wires at splice and
remove Gnd wire from GND terminal. Install new motor in reverse order.
E. AFT Evaporator Blower will not operate in the low speed setting.
1. Connect ground power to aircraft.
2. Select air conditioning system to ON.
3. Check if power is present at wire EVAP-AL (at splice). If power is present,
the low speed resistor (Ref. 21-50-05 IPL Fig. 1, item 9) has failed.
4. Select air conditioning OFF, remove electrical power.
5. Remove blower assembly and using a #21 drill remove the two rivets
securing the resistor. Cut the wires at the splice and remove GND wire from
GND terminal. Install new resistor in reverse order.
Products, Inc.
Maintenance Manual
21-50-01
May 15/95
Page 1001
Figure 1. Electrical System
Products, Inc.
Maintenance Manual
21-50-01
May 15/95
Page 1002
FIG. ITEM
PART
NUMBER
NOMENCLATURE
EFFECT
UNITS
PER
ASSY
1 1
2
3
4
5
6
7
8
9
10
11
12
13
14
82-02-106
JBS11001-1
MS3320-15
MS25361-100
ES32036-1
JBS5005-1
JBS2030-3
JBS2048-3
MS25181-2
MS25036-101
ES50162-1
MS25036-125
MS25036-157
MS25036-123
Electrical Installation
Light (Blue)
Circuit Breaker
Circuit Breaker
Grommet
Compressor/Condenser
FWD Evaporator
AFT Evaporator
Butt Connector
Terminal
Lamp
Terminal
Terminal
Terminal
RF
1
1
1
1
1 ref
1 ref
1 ref
7
5
1
1
1
1
Air Conditioning System - Electrical System
IPL FIGURE 1
Products, Inc.
Maintenance Manual
21-50-01
May 15/95
Page 1003
FIG. ITEM
PART
NUMBER
NOMENCLATURE
EFFECT
UNITS
PER
ASSY
15
16
17
18
21
22
23
24
25
26
MS25036-106
MS25036-108
84-00-07-8
ES57016-3
ES53010-3
MS25036-124
MS25036-156
ES55077-2
ES57016-6
ES57016-5
Terminal
Terminal
Load Shed Assy
Switch
Connector
Terminal
Terminal
Terminal
Switch
Switch
15
3
1
1
1
1
1
1
1
1
Air Conditioning System - Electrical System
IPL FIGURE 1