AirComm Corporation Cessna 414 421 Air Conditioning System Service Manual R134a

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2.2 Electrical Driven Compressor Systems 
 
Electrically operated systems use the aircraft electrical system and are operable 
in most normal flight modes.  Air conditioning may be operated with ground 
external power or the aircraft electrical system providing voltage to the proper 
bus. 
 
The compressor and condenser are manufactured on an assembly pallet. In 
most cases, the compressor drive and condenser fan drive are both driven by a 
common, double shafted motor.  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 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.  Some electrically driven 
systems have separate compressor drive and condenser fan motors.  After 
passing through the condenser coil, the air is exhausted to the outside.  The 
compressor takes low pressure refrigerant gas and compresses it to a higher 
pressure and temperature.    
    
On the ground, the electrical system allows operation of the air conditioning 
system from either aircraft generator or from an active GPU prior to engine start. 
Some 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 aircraft generators on line.  Loss of aircraft generator power 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 and 
over temperature 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 safety overpressure 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.  
						

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2.3  Engine Driven Compressor Systems 
 
Engine driven systems use compressors that are engine mounted; or on some 
rotorcraft, driven off the tail rotor drive shaft.  A pulley via a V type belt turns the 
compressor.    A clutch mounted on the compressor engages the compressor 
when the air conditioning system is selected ON. 
 
The condenser uses a separate fan with electrical motor to supply cooling air.  
The condenser cooling air (ambient air) is drawn in through a cutout in the 
fuselage skin of the aircraft and passes through the condenser coil to remove 
heat from the system.  After passing through the condenser coil and blower, the 
air is exhausted to the outside of the aircraft.  
 
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.  This switch will open at approximately 350 PSIG and will 
interrupt power to the compressor clutch at which point the system pressures will 
drop. The switch will also interrupt power to the compressor clutch under low 
pressure conditions.   The second overpressure safety device is a fuse plug 
which will vent the system refrigerant in the event of a system pressure in excess 
of 425 PSIG.  It is located on the receiver/drier.   
						

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3.0 REFRIGERANT SERVICING 
 
3.1 General 
 
The air conditioning system uses refrigerant R134a and the compressor 
lubricating oil used is Polyolester Oil viscosity grade (ISO) 68.  No other 
refrigerant or compressor oil should be used. 
 
Refrigerant R134a is non explosive, non-flammable, non -corrosive, has 
practically no odor, and is heavier than air.  Although R134a is classified as a 
safe refrigerant, certain precautions must be observed to personnel and property 
when working with R134a refrigerant. 
 
WARNING:   
 
A.  Liquid R134a, at normal atmospheric pressure and temperature, 
evaporates so quickly that it tends to freeze anything that it contacts.  Care must 
be taken to prevent any liquid refrigerant from coming into contact with skin. 
 
B.  Always wear safety goggles when servicing any part of the refrigerant 
system to prevent refrigerant from coming into contact with the eyes. 
 
C.  To avoid explosion, never weld, use a blow torch, solder, steam clean, or 
use excessive amounts of heat on, or in, the immediate area of the air 
conditioning system, or refrigerant supply tank, full or empty, while they are 
closed to atmosphere. 
 
D.  The refrigerant service cart/container has a safe strength.  However, if 
handled incorrectly, it will explode.  Therefore, always follow the instruction on 
the label.  In particular, never store it in a hot location (above 126F, 52C) or 
drop it. 
 
CAUTION:  Do not operate air conditioning system with condenser air outlet 
blocked.  
						

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3.2 Discharging System 
 
A. General 
 
The air conditioning system refrigerant must be discharged prior to disconnecting 
or removing components in the refrigerant loop.  Federal law prohibits 
discharging refrigerant into the atmosphere.  Use only an R134a compatible 
recycling/recovery unit when discharging the air conditioning system. 
 
 
B. Tools and Equipment 
 
 
Designation Ref. No.  
Qty  
Remarks 
 
 
Service Pressure Gauge  Comm. Avail.  
1  
None 
 
R134a Compatible 
Recycling/Recovery 
Unit Comm. Avail.  
1  
None 
 
 
C. Discharging Procedure 
 
1)  Connect R134a compatible recycling/recovery unit to the R134a service 
valves on the aircrafts air conditioning system.  If recovery unit does not 
have pressure gauges, connect service pressure to air conditioning system. 
 
2)  After cart oil level has been verified, evacuate the system, per recovery 
unit’s instructions.  Let the system sit for approximately 5-10 minutes to let 
any residual refrigerant boil from the system oil. Note the amount of post 
recovery oil in cart.  The amount of oil in the cart prior to recovery should be 
subtracted from the amount of oil after recovery. This is the amount of oil 
that needs to be added to the system before charging. 
 
3)  Remove recovery unit when discharging is complete.  
						

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3.3 Evacuating System 
 
A. General 
 
The air conditioning system must be evacuated prior to charging the system with 
refrigerant.  Evacuating the system removes any moisture that may be in the 
system.  Use only an R134a compatible recycling/recovery unit when evacuating 
the air conditioning system. 
 
 
B. Tools and Equipment 
 
 
Designation  
Ref. No.  
Qty  
Remarks 
 
 
Service Pressure Gauge  
Comm. Avail.  
1  
None 
 
R134a Compatible 
Recycling/Recovery 
Unit  
Comm. Avail.  
1  
None 
 
 
C. Evacuating Procedure 
 
1)  Connect R134a compatible recycling/recovery unit to the R134a service 
valves on the aircrafts air conditioning system.  If recovery unit does not 
have pressure gauges, connect service pressure to air conditioning 
system. 
 
2)  Evacuate the air conditioning system in accordance with the recovery 
units instructions for a minimum of 15 minutes. 
 
3)  Once the air conditioning system has been evacuated, it is then ready 
for charging with new/recycled R134a refrigerant.  
						

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3.4 Charging System 
 
A. General 
 
Use only R134a refrigerant when charging air conditioning system.  Federal law 
prohibits discharging refrigerant into the atmosphere.  Use only R134a 
compatible recycling/recovery unit when charging the air conditioning system. 
 
B. Tools and Equipment 
 
 
Designation  
Ref. No.  
Qty  
Remarks 
 
 
Service Pressure Gauge  
Comm. Avail.  
1  
None 
 
R134a Compatible 
Recycling/Recovery 
Unit  
Comm. Avail.  
1  
None 
 
Polyolester Oil  
Comm. Avail  
A/R  
Viscosity ISO 68 
 
C. Charging Procedure 
 
1)  Connect R134a compatible recycling/recovery unit to the R134a service 
valves on the aircrafts air conditioning system.  If recovery unit does not have 
pressure gauges, connect service pressure to air conditioning system. 
 
2)  Add the amount of compressor oil recovered during discharging.  Add new 
polyolester oil, viscosity ISO 68 to the compressor oil fill port. 
 
3)  Charge the air conditioning system in accordance recovery unit’s 
instructions, until: 
a. The sight glass just clears of bubbles.  This can also be 
accomplished by first initially charging the system with 1.5 lbs of 
refrigerant and then VERY slowly, with the system operating, 
introduce small amounts of refrigerant in .1 lb increments until the 
sight glass is clear of bubbles. (If sight glass is present.) 
b.  The charge pressure reaches the range specified in the Table A.1.  
(If no sight glass is present) 
 
NOTE:  Keep the low side closed and the high side open during charging so 
that liquid R134a passes through the evaporator and evaporates into a gas 
before entering the compressor.  Liquid R134a entering the compressor can 
cause permanent damage!  
						

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3.5 Flushing System 
 
A. General 
 
The following procedure is used to whenever the compressor is replaced and 
when system contamination is suspected. 
 
B. Tools and Equipment 
 
Designation Ref. No. Qty Remarks 
ACC Hose Coupler Tool  See Procedures  A/R  None 
Service Pressure Gauge  Comm. Avail.  1  None 
R134a Compatible 
Recycling/Recovery Unit Comm. Avail.  1  None 
Polyolester Oil  Comm. Avail.  A/R  Viscosity ISO 68 
 
System Flushing Procedure 
 
1.  Connect the refrigerant recovery cart to the normal service ports. 
 
2.  Empty the refrigerant recovery cart’s oil collection tube so that it begins with 
zero oil collected. 
 
3. Discharge the air-conditioning system and recover the refrigerant per the 
refrigerant cart’s instructions.  Do not empty the oil collection tube. 
 
4.  Disconnect the refrigerant recovery cart from the normal service ports. 
 
5.  Remove the compressor and connect the service valve couplers to the suction 
and discharge plumbing hoses. 
 
  O-ring Style Coupler P/N’s JBS6020-7 and JBS6020-8. 
  Flare Style Coupler P/N’s JBS6020-9 and JBS6020-10.  
 
6.  Bypass the binary pressure switch.  If located on the condenser assembly, 
attach the plumbing hose directly to the condenser.  If located on the 
compressor then bypass per previous step. 
 
7.  Remove the receiver/drier bottle from the aircraft and properly dispose.  Attach 
the hose coupler tool in place of the receiver/drier bottle.  
 
  O-ring Style Coupler P/N JBS6009-1. 
  Flare Style Coupler P/N JBS6020-6.  
						

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8.  Disconnect all of the expansion valves from the evaporator assemblies.  Attach 
the hose coupler tool in place of the expansion valves on all evaporator 
assemblies.  Use caution in handling the expansion valves.  Do not support the 
expansion valve by its remote bulb tubing.  Do not disconnect the external 
equalization port fitting if the expansion valve is an externally equalized style 
(ES26105-1 and ES26106-1). 
 
  O-ring Style Coupler P/N JBS6020-3 
  Flare Style Coupler P/N JBS6020-4 
 
9.  Connect the refrigerant recovery cart to the service port couplers located where 
the compressor was removed to create a refrigerant loop with the refrigerant 
cart. 
 
10. Evacuate the system thru the HIGH side port only per the refrigerant recovery 
cart’s instructions for a minimum 10 minutes. 
 
11. Charge the system thru the LOW side port only with 1.5 to 2 times a normal 
refrigerant charge of refrigerant.  Do not add any oil to system. 
 
12. Recover the system thru the HIGH side port only per the refrigerant recovery 
cart’s instructions. 
 
13. Repeat previous three steps two additional times. 
 
14. Disconnect the refrigerant recovery cart from the service ports. 
 
15. Remove the compressor and drain all of the oil from the compressor into an 
empty graduated cylinder.  It will be necessary to rotate the clutch plate several 
times to get as much oil as possible from the compressor. 
 
16. Empty the refrigerant recovery cart’s oil collection tube into the graduated 
cylinder with the drained compressor oil.  Inspect the oil for debris 
contamination and replace compressor if necessary. 
 
17. New compressors come serviced with 5 ounces of oil and do not require oil 
adjustment.  If the existing removed compressor is reused or other replacement 
compressor for which the oil level is unknown, then completely drain the 
compressor and then add 5 ounces of new polyolester oil ISO grade 68 to the 
compressor.  Torque the oil plug to 6 to 9 ft-lbs. 
 
18. Install the compressor.  Use new o-rings. 
 
19. Inspect the expansion valves for damage and debris.  Replace if any 
contamination is found.  Use new o-rings.  
						

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20. Inspect the binary pressure switch for damage and debris.  Flush with dry 
nitrogen or clean dry compressed air before re-installing.  Use new o-rings. 
 
21. Install a new receiver/drier bottle.  Do not reuse the old bottle under any 
circumstance.  Use new o-rings. 
 
Caution:   Receiver/drier bottles left open to the atmosphere for more than 10 
minutes must be discarded and replaced with new. 
 
22. Evacuate the system per the refrigerant recovery cart’s instructions for a 
minimum 15 minutes. 
 
23. Add 1 ounces of new polyolester oil ISO grade 68 for each 7 feet of plumbing 
over 15 feet total length to the system thru the HIGH side port only. 
 
24. Charge the system per Charging Procedure.  
						

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4.0 GENERAL SERVICING 
 
4.1 General 
 
General service procedures are provided to keep the air conditioning system 
operating at peak efficiency.  Procedures are provided for general maintenance 
tips, inspection intervals, maintenance of the plumbing system, to repair hoses, 
and to clean coils.  Procedures are also provided for removal and installation of 
the expansion valve. 
 
CAUTION:  Do not operate air conditioning system with condenser air outlet 
blocked. 
 
4.2 Inspection Intervals 
 
A. General 
 
Periodic inspections of the air conditioning system will keep the system operating 
at peak efficiency.   The inspections are simple visual inspections requiring a 
minimal amount of time.  
 
B. Inspection Intervals 
 
 
ITEM  
INSPECT FOR INTERVAL  
ACTION 
 
Air Conditioning 
System 
Components  
Dirt , Damage *Every 500 hours 
and annualy  
Clean or replace 
component as 
necessary 
 
Compressor Belt  
Tension, Wear Within 5 hours of 
installing new belt 
*Every 500 hours 
and annualy  
Tension or replace 
as necessary 
 
Sight Glass  
(if so equipped)  
Proper refrigerant 
level When problem is 
suspected  
Discharge/charge as 
necessary per 
Refrigerant Servicing 
section 
 
Evaporator and 
condenser coils  
Dirt *Every 500 hours 
and annualy  
Clean as necessary 
 
*Recommended inspection interval maximums.  Actual inspection times should 
be conducted around the aircrafts existing regularly scheduled maintenance 
checks.