AirComm Corporation Bell 412 Air Conditioner Instructions for Continued Airworthiness User Manual

							AIR CONDITIONER SERVICE MANUAL 412AC-208M 
 
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CHAPTER 1 
INTRODUCTION 
1. SCOPE 
The scope of this manual encompasses the scheduled and unscheduled maintenance 
procedures for the continued airworthiness of the Air Comm Corporation air conditioning 
system installed in the Bell 412 series helicopter. 
 
2. PURPOSE 
The purpose of this manual is to provide the aircraft mechanic in the field the necessary 
information to maintain the air conditioning system. 
 
3. ARRANGEMENT 
This manual is arranged by chapters which are broken down into paragraphs and sub-
paragraphs. All of the chapters and paragraphs are listed in the front of this manual in 
the Table of Contents, and are further identified by their individual page number. 
 
4. APPLICABILITY 
This manual is applicable to Bell Helicopter models 412, 412SP, 412HP, 412EP, and 
412CF that are both Non-NVIS and NVIS equipped with an Air Comm Corporation kit 
number 412AC-102-1 thru 412AC-102-6 air conditioner system. 
 
5. DEFINITIONS 
The following terms are provided to give a ready reference to the meaning of some of 
the words contained within this manual. These definitions may differ from those given by 
a standard dictionary. 
A. Ambient air temperature: The temperature of the air surrounding a person or 
object. 
B. Charging station: A piece of air conditioning equipment which normally contains 
a vacuum pump, manifold set, and a method of measuring and dispensing 
refrigerant into a system. 
C. Condensation: The process of changing a vapor into a liquid. 
D. Desiccant: A material used in the receiver/drier bottle, designed to absorb 
moisture from the refrigerant. 
E. Evaporate: To change from a liquid into a vapor. 
F. Heat load: The amount of heat which the air conditioner is required to remove 
from the aircraft cabin. 
G. Inches of mercury: A measurement of pressure, normally used for pressures 
below atmospheric, one inch of mercury is equal to approximately one half pound 
per square inch. 
H. Pressure, ambient: The pressure of the air surrounding a body, normally 
measured in Pounds per Square inch, or PSI. 
I. Refrigerant: A fluid which is used in an air conditioning system to absorb heat 
from the cabin and carry it outside the helicopter where it can be transferred to 
the outside air. 
J. Relative humidity: The ratio of the amount of water vapor in the air to the 
amount of water vapor required to saturate the air at the existing temperature. 
K. Thermostat: An air conditioning control which senses the temperature of the 
evaporator coil and causes the system to cycle or by-pass to maintain the proper 
temperature of cooling air. 
L. Vacuum: A negative pressure, or pressure below atmospheric; it is usually 
expressed in inches of mercury. 
M. Vapor: The gaseous state of a material. 
  
						

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6. ABBREVIATIONS 
InHg:  Inches of Mercury 
Lbs:  Pounds 
Oz:  Ounces 
Psig:  Pounds per Square Inch (guage) 
gr:  Grams  
kg:  Kilograms 
Kg/Cm: Kilograms per Centimeter 
ml:  Milliliters 
mm:  Millimeters 
Nm                  Newton-meters 
 
7. PRECAUTIONS 
The following precautions are found throughout this manual, and will vary depending on 
the seriousness of the Hazard or Condition: 
 
a. WARNING: May be a maintenance procedure, practice, condition, etc., which 
could result in personal injury or loss of life. 
b. CAUTION: May be a maintenance procedure, practice, condition, etc., which 
could result in damage or destruction of equipment. 
c. NOTE: May be a maintenance procedure, practice, condition, etc., or a 
statement which needs to be highlighted. 
 
8. UNITS OF MEASUREMENT 
 All measurements contained within this manual are given in the United States standard 
measurement, followed by the metric conversion in parentheses.  
 
9. INFORMATION ESSENTIAL TO THE CONTINUED AIRWORTHINESS OF THE AIR 
CONDITIONER 
This manual provides information which is required for operation and maintenance of the 
Air Comm, air conditioning system installed in the Bell model 412 series helicopter. After 
completion of the air conditioner installation this document must be placed with the 
appropriate existing aircraft documents. 
 
10. REFERENCE DOCUMENTS 
The documents that are listed below are General Arrangement and Installation drawing 
packages. While these drawings are primarily for the installation of the air conditioner 
system, they are of equal importance in aiding the operator and mechanic in the field to 
ensure the continued airworthiness of this system. 
 
1. Dwg. 412AC-102-1 / -2 / -3 General Arrangement – Bell model 412, 412SP, 
412EP, 412HP, and 412CF Air Conditioning system with Temperature Control. 
2. Dwg. 412AC-304 Compressor Installation. 
3. Dwg. 412AC-508 / -518(CF) Plumbing Installation. 
4. Dwg. 412AC-608 Forward Evaporator Installation. 
5. Dwg. 412AC-604 Aft Evaporator Installation. 
6. Dwg. 412AC-712 Condenser Installation. 
7. Dwg. 412AC-818 Electrical Installation. 
8. AC43.13-1A Acceptable Practices, Aircraft Maintenance and Repair. 
9. Bell Airframe Repair Manual. 
  
						

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11. DISTRIBUTION 
This  document  is  to  be  placed  with  the  aircraft  maintenance  records at  the  time  of 
system installation. 
Changes  will  be  made  to  this  document  in  response  to  “Safety  of  Flight”,  and  or  “Non-
safety of Flight” issues. Any changes will result in a revision to this document. Revisions 
shall be noted in the Record of Revisions (page i), and on the List of Revisions (page ii) 
of this manual. 
In addition to the revision of the manual, those changes categorized as “Safety of Flight” 
shall  have  a  Service  Bulletin  issued  to  the  operator  providing  the  necessary  information 
to comply with, and or to correct, the “Safety of Flight” issue. 
Replacement, and or revised copies of this manual maybe acquired by contacting: 
Air Comm Corporation Service Department 
1575 W. 124th Ave STE 210 
Westminster, CO.80234 
Phone No. 303-440-4075 Fax No. 303-440-6355 
[email protected] 
 
12. CHANGES TO THIS MANUAL 
Changes made to a line or paragraph of this document will be indicated by a vertical bar 
in the right hand margin, while a complete page change will be indicated by a vertical bar 
next to the page number. 
 
(Example: Any changes will appear with a vertical bar next to that change). 
 
13. AIR CONDITIONER FEATURES 
 The vapor cycle air conditioner features two forward mounted evaporators (cockpit), one 
aft mounted evaporator (main cabin), one condenser, and a compressor driven by the 
main transmission drive shaft. These components combine to provide “conditioned air” 
through the existing air distribution system, when the engines are operating during both 
ground and flight operations. 
 
 This system can be operated in either the Air Condition (A/C), or Blower mode.  
 
In the A/C mode, conditioned air is provided by the forward and aft evaporators to the 
cockpit and main cabin areas respectively. 
 
 In the Blower mode, the evaporator blowers are used to circulate cabin air, while the 
compressor clutch remains disengaged. 
 
If desired, the cabin heater can be operated simultaneously with the A/C or blower mode 
to achieve the desired cabin temperature, or help defog the cabin windows. 
 
 The air conditioning system is connected electrically to the aircraft’s non-essential bus, 
thus the air conditioner drops off-line in the event of a failure of either engine. 
 
The control panel for the air conditioner system is located in the center pedestal between 
the pilots and co-pilots seats. This panel consists of a temperature control knob, 
annunciator light (which shows on when the system is operating), the A/C & Blower 
on/off switch, and the Hi/Lo switches for the forward and aft evaporator blowers. 
  
						

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Figure 1:  Cockpit A/C Control Panel 
The blower motors are two speed operation (Hi/Lo), and may be operated in conjunction 
with the A/C or Blower modes.  
 
The compressor is mounted on the aft side of the main rotor transmission housing. This 
compressor is driven by two V-belts and three pulleys arranged to reduce the speed 
transmitted by the transmission input quill. 
 
Airflow through the condenser heat exchanger is provided by two (2) seven inch 
diameter 28 volt DC high performance vane axial blowers. The airflow is further 
augmented by ram air provided through two cutouts located on the front of the upper 
transmission cowling, while the helicopter is in forward flight. 
 
The aft evaporator assembly is equipped with a thermistor / electronic temperature 
control unit. The thermistor probe is located in the core of the evaporator heat 
exchanger. This unit performs two functions; 1. It acts to prevent coil freeze-up by 
limiting the minimum coil temperature to 32º F (0º C), and 2. It acts as a cabin air 
temperature control system, by controlling the by-pass of refrigerant through the 
evaporator coil when the temperature control switch on the control panel is turned up. 
 
The refrigerant plumbing for this system installation incorporates two different types of 
O-ring fittings: 
 
1. INSERT O-RING FITTINGS: These fittings have formed ends that, along with an O-
ring, create a seal. Care should be taken when assembling these fittings not to 
damage the O-ring (i.e. nicking, splitting, or crushing, etc.). The insert O-ring hose 
and tube ends are identified by green bands adjacent to the fitting. The band color 
corresponds to the color of the O-ring to be installed at that location. The black 
O-rings must not be used on these fittings. (See page 6-1 for torquing procedures). 
 
2. TORQ LOK® O-RING FITTINGS: These fittings feature a face type O-ring seal. 
These fittings are much easier to assemble then that of the insert type. Care should 
be taken when assembling these fittings not to damage the O-ring. The TORQ LOK® 
O-ring hose and tube fittings are identified by a black band adjacent to the fitting. The 
band color corresponds to the color of the O-ring to be installed at that location. The 
green O-rings must not be used on these fittings. (See page 6-1 for torquing 
procedures). 
 
The system is also equipped with a Hi/Lo pressure switch. This switch is designed to 
protect the system against over-pressure situations, or in the event of refrigerant loss 
from the system. The switch also prevents the system from operating in low ambient 
temperatures below 50º F (10º C).  
						

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The switch operating pressures are: 
 
Low Pressure Function: 
Cut-out at 28.4 ± 2.8 psi (2.0 ± 0.2 Kg/Cm²) 
Cut-in at 30.0 ± 4.3 psi (2.1 ± 0.3 Kg/Cm²) 
 
High Pressure Function: 
Cut-out at 290 ± 28.4 psi (20.4 ± 2.0 Kg/Cm²) 
Cut-in at 200 ± 42.7 psi (14.0 ± 3.0 Kg/Cm²) 
 
14. DESCRIPTION OF THE AIR CONDITIONER AND ITS INSTALLATION 
This section contains a general overview of a Vapor-cycle air conditioning system and 
how it functions. As the name implies, this type of system operates in a closed loop in 
which the refrigerant picks up heat from the cabin, and takes it to be released into the 
outside air. The refrigerant then returns to the cabin to repeat the cycle. The operation of 
the system is described below. 
 
Liquid refrigerant is contained in the receiver-drier under pressure from the compressor. 
The receiver-drier also filters the refrigerant through a material know as desiccant. The 
desiccant ensures that the fluid leaving this component is free of any water or other 
contaminants. 
 
The low pressure (suction line) from the compressor is attached to the evaporator lines, 
and causes the refrigerant to be pulled out of the receiver-drier and through the 
expansion valves. The expansion valves serve as a controlled spray orifice, to spray the 
correct amount of refrigerant into the evaporator. 
 
 This regulation of refrigerant allows the liquid to absorb the heat from the cabin air, and 
transforms it to a vaporous state just prior to exiting the evaporator assembly. This 
extraction of heat is the cooling action that the system is designed to achieve. 
 
The low pressure vapor is then drawn into the compressor where its pressure is raised 
to approximately 200 psi, and its temperature to around 200º F (93.3º C). This high 
pressure / high temperature vapor then travels to the condenser, (a heat exchanger 
cooled by a flow of outside air). Heat is extracted from the refrigerant, and as it cools it 
condenses back into a liquid and flows into the receiver-dryer, ready to repeat the cycle. 
  
						

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15. Refrigeration Cycle Illustration 
NOTE: This illustration is provided as a reference only and may not match actual  
   installation 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
 
  
 
        High pressure liquid 
        High pressure vapor 
        Low pressure liquid 
        Low pressure vapor 
        Expansion valve        
         By pass line 
 
Figure 2:  Refrigeration Cycle Illustration 
 
 
Receiver-Dryer 
Aft Evaporator 
Forward 
Evaporators 
Compressor 
Condenser 
Bypass Valve  
						

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CHAPTER 2 
AIRWORTHINESS LIMITATION SECTION 
 
 
1. Airworthiness Limitations 
 
The  Airworthiness  limitations  section  is  FAA  approved  and  specifies  inspections  and 
other  maintenance  required  under  Sections  43.16  and  91.403  of  Federal  Aviation 
Regulations unless an alternative program has been FAA approved. 
 
 No airworthiness limitations are associated with this type design change. 
 
 
 
FAA approval: 
       
ACO Representative                                                                             Date 
						

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CHAPTER 3 
 INSPECTIONS   
1. INSPECTION REQUIREMENTS 
 
PERIODIC INSPECTIONS  
          (Hours are aircraft time)  
Item Prior to Cooling Season 
Every 25 Hours of Operation, +/- 3 hrs. 
Every 100 Hours of Operation, +/- 10 hrs. Special Inspection Information  
Evaporator Blower Hi/Lo Operation X  X Check for operation and security.  
Condenser Blower Motor & Fan Assy. X  X Check for operation and security. See Overhaul / Replacement Schedule below. 
 
Condenser Assy. Mounting & Housing X  X Check for blockage of heat exchanger fins, operation, and security. 
 
Compressor Drive Belts for Tension & Wear X X X Check belt tension for signs of excessive wear, check drive pulleys for security and wear. 
 
Placards & Markings X  X Check for security and legibility.  
Compressor Assy. X X X 
Check for operation, security of attaching hardware, and signs of oil or refrigerant leaks. See Replacement Schedule below. 
 
Compressor Mount X X X Check for operation of the speed reducer drive pulley, and security of the attaching hard ware. 
 
Aft Evaporator Foam Insulation X   Check for security and signs of deterioration, replace as necessary.  
Plumbing and Fittings X  X Check for security and signs of oil or refrigerant leaks.  
Speed Reducer Bearing X X X 
Apply a 2 to 3 lb (.9 to 1.4 Kg) force to the edge of the pulley, as shown by Figure 110, Page 32 Any free-play of the pulley/bearing assembly in the direction X-X is cause for immediate replacement of bearing. 
 
 
  
2. COMPONENT OVERHAUL / REPLACEMENT SCHEDULE 
(Hours are aircraft time)  
Description Part Number Overhaul / Replacement Hours  
Condenser Blower 412AC-7058-15 Motor & Fan replacement 
ES73131-1 (New) ES73131-2 (Overhauled) 
The blower manufacturer recommended TBO is 600 hrs. At the discretion of the operator it is acceptable to operate the blower until failure. A blower failure will result in a reduction in cooling. 
 
Compressor Assy. 412AC-3542-2 
The compressor manufacturer recommended TBO is 900 hrs. At the discretion of the operator it is acceptable to operate the compressor until failure. A compressor failure will result in a loss of cooling. 
 
Speed Reducer Bearing 
 ES33100-3  (35BD219DUM Obsolete Bearing) 
It is recommended that the Speed Reducer Bearing be replaced every 900 hours of operation.  A bearing failure could result in a broken belt and loss of cooling. 
 
  
						

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3. INSPECTION PROCEDURES  
 
NOTE 
Refer to “Chapter 4 location and access” to locate all components for inspection. 
 
A. Inspection of the FWD and AFT evaporator blower motors 
 
CAUTION 
Fans are designed to operate with the resistance of the entire ducting system. 
Operation of the evaporator fans with any part of the distribution system removed may 
cause permanent damage to the fan motor. 
 
WARNING 
Fans may take up to 10 seconds to start after the switch is turned on. Keep hands 
away from fan whenever switch is in BLOWER or A/C positions. 
 
a. At the Cockpits Air Conditioner Control Panel place the AIR COND 
switch in the BLOWER position and verify: 
1. That both the fwd and aft fans are activated and operating – 
Place blower switches to “low” and “high” to verify blowers 
increase and decrease speed accordingly. 
2. That the condenser fan is non-operational. 
3. That the compressor clutch is disengaged. 
 
b. Place the AIR COND switch in the OFF position and verify that: 
1. That both the fwd and aft fans deactivate 
2. That the compressor clutch remains disengaged.  
 
B. Inspection of the air conditioner condenser 
 
NOTE 
This inspection may be performed with the air conditioner charged with refrigerant 
or it may be performed with no refrigerant in the system. In the case where there is 
no refrigerant in the system or the system is low on refrigerant or in the case where 
the ambient temperature is low, the binary switch will need to be jumpered. The 
temporary installation of a jumper wire across the terminals of the binary switch will 
do no harm even if it was not necessary. 
 
CAUTION 
 
The temporary jumper must be removed after this inspection is completed. 
 
a. Visually inspect condenser air inlet for any obstructions or debris. 
Airflow in this area is critical for air conditioner operation. 
b. Install a jumper between the contacts of the binary switch if required. 
c.  Connect 28V ground power to the aircraft and place the A/C mode 
switch in the “A/C” position and verify that: 
1. Condenser fan is activated and operating. This fan should pull air 
into the aircraft. 
2. Compressor clutch is engaged. Verify compressor clutch 
engagement by visually observing the clutch plate clamp to the 
compressor rotor or an audible click when the switch is moved to 
“on”.  
						

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d. Place the A/C mode switch into the Off position and verify that the 
condenser fan is deactivated. 
e. Ensure that the jumper wire is removed from the binary switch. 
 
C. Inspection of compressor drive belt 
a. Remove transmission cowling to gain access to compressor drive 
belt and visually inspect the A/C compressor drive belt for the 
following: 
1. Any signs of excessive wear. 
2. Any signs of glazing. 
3. Any cracks or missing pieces. 
4. Any exposed fibers. 
b. Verify proper belt tension as shown in the illustration shown in Figure 
3. Below. 
 
 
Figure 3:  belt tension inspection 
 
D. Inspection of air conditioner placards and markings. 
a. Check all air conditioner placards and markings for security and 
legibility. 
 
E. Inspection of air conditioner compressor assembly 
NOTE: 
The air conditioning system must be serviced with refrigerant to perform this 
inspection 
a. Connect 28V ground power to the aircraft and place the A/C mode 
switch in the “A/C” position and verify: 
1.  Compressor clutch is engaged. 
b. Place air conditioner switch to the OFF position and verify: 
1. Compressor clutch is disengaged.  
c. Visually inspect the compressor assembly for the following:  
1. Security of all attaching hardware. 
2. Signs of refrigerant or oil leaks.  
3. Signs of excessive belt slippage or excessive heat.