AirComm Corporation Cessna 414 421 Air Conditioning System Service Manual R134a

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4.3  Plumbing System Maintenance Procedures 
 
A. General 
 
The following procedures are used to perform typical maintenance on the air 
conditioning system plumbing.  Procedures are provided for hose or fitting 
replacement.  New ACC air conditioning systems use swaged hose fittings.  
Some systems that have been converted from R12 to R134a refrigerant use Barb 
Lok hose fittings.  Fittings are either o-ring type or use flared connections. 
 
B. Tools and Equipment 
 
 
Designation  
Ref. No.  
Qty  
Remarks 
 
 
R134a Compatible Hose Swaging 
Kit  
Available from 
ACC  
1  
None 
 
Sharp Knife  
Comm. Avail.  
1  
None 
 
Impact Wrench  
Comm. Avail.  
1  
None 
 
Light Machine Oil  
Comm. Avail.  
A/R  
None 
 
Polyolester Oil  
Comm. Avail.  
A/R  
Viscosity ISO 68 
 
Sealant  
ES49000-1  
A/R  
None 
 
C.  Hose or Fitting Replacement (Swaged Hose Fittings) 
    
NOTE:  If it is found that a hose or fitting has a leak, it will be necessary to 
replace the entire hose assembly.  Follow the Hose Swaging Instruction below: 
 
1.  Hose should only be cut with a sharp knife.  (Note:  Use of serrated 
blades or saws to cut hose will leave particles that can contaminate system.) 
2.  Insert the proper size die in the swaging tool. 
3.  Insert fitting in swaging tool so that it is centered in the die and hand 
tighten. 
4.  Insert hose in fitting until it bottoms (Note:  Indicating hole is in base of 
fitting). 
5.  Using impact wrench, tighten nut until die housings contact.  (Note:  It is 
important to keep hose pushed into fitting while swaging). 
6.  Reverse impact and back off nut until housing contacts rubber stops.  
						

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D.  Hose or Fitting Replacement (Barb-Lok Hose Fittings) 
 
NOTE:  If it is found that a hose or fitting has a leak, it will be necessary to 
replace the entire hose assembly.  Follow the Hose Barb-Lok Instruction below: 
 
1.  Hose should only be cut with a sharp knife.  (Note:  Use of serrated 
blades or saws to cut hose will leave particles that can contaminate system.) 
2.  Slide the Barb-Lok socket onto the hose fitting with the round end towards 
the stop.  Apply a few drops of machine oil to nut to ease installation.  (Note:  Do 
not lubricate fitting barbs.) 
3.  Push hose on barbed end of fitting until all barbs are covered.  Hose end 
shall be about 1/8 inch past last barb. 
4.  Hold hose in place.  Pull socket towards hose and thread onto hose 
counter-clockwise. Use wrench to turn socket onto hose.  The round end of the 
socket should be 0.82 inch (or one socket length) from the push-on hose stop. 
5.  About 1/8 inch of hose should protrude past the socket.  This may be 
trimmed to improve the appearance of the hose assembly. 
 
E.  Connection to Components - O-Ring Replacement 
1.  Place the appropriate o-ring over the tube O end of the fitting.   
2.  Lubricate o-ring with polyolester oil or sealant prior to assembly. 
3.  Apply sealant to all fitting mating surfaces prior to assembly. 
 
F.  Recommended standard dry torque specifications. 
 
Thread 
Size O-Ring Flare 
FT-Lb N-M  FT-Lb N-M 
5/8” 11-13 15-18 20-25 27-34 
3/4 15-20 20-27 35-40 47-54 
7/8” 21-27 29-37 50-60 68-81 
1 1/16”  28-33  38-45 70-80 95-108 
 
G.  Connection to Components - Flared Fittings 
1.  Apply sealant to all fitting mating surfaces prior to assembly. 
 
H. Receiver/Drier Replacement 
1.  Replace receiver/drier whenever the compressor is replaced or 
when the air conditioning system plumbing is left open to the atmosphere for a 
period of time greater than 10 minutes.  
						

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4.4  Coil Cleaning Maintenance Procedures 
 
A. General 
 
The following procedure is used for cleaning either evaporator or condenser coil. 
B. Tools and Equipment 
 
 
Designation  
Ref. No.  
Qty  
Remarks 
 
 
Vacuum Cleaner  
Comm. Avail.  
1  
None 
 
Coil Cleaner  
Comm. Avail.  
A/R  
Non-acid based 
 
C.  Coil Cleaning Procedure 
1.  Use vacuum cleaner to remove large debris from upstream and 
downstream coil faces. 
2.  Spray coil cleaner on both coil faces.  Wash off with water. 
3.  Allow coil to dry thoroughly prior to additional maintenance.  
						

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4.5  Expansion Valve Removal and Installation 
 
A. General 
 
The following procedure is used to remove or install the air conditioning system 
expansion valve. 
 
B. Tools and Equipment 
 
Designation 
  
Ref. No.  
Qty  
Remarks 
 
Sealant  
ES49000-1  
A/R  
None 
 
Polyolester Oil  
Comm. Avail.  
A/R  
Viscosity ISO 68 
 
C. Expansion Valve Replacement 
 
1.  Discharge system in accordance with Refrigerant Servicing section. 
2.  Disconnect liquid line from inlet of expansion valve, and cap. Remove the 
thermal sense bulb from its clamp located on the suction tube of the 
evaporator and carefully remove insulation covering bulb. 
3.  Disconnect the fitting that connects the valve to the coil and plug coil 
fitting. 
4.  Install new expansion valve and o-ring (for o-ring fitting systems) in the 
reverse order.  
5.  Lubricate o-ring with polyolester oil or apply sealant to fitting mating 
surfaces prior to assembly. 
6.  Install the thermal sense bulb such that it makes contact with the suction 
tube along its entire length. When viewing the suction tube extruding out 
of the evaporator, the sense bulb should be in the three or nine o’clock 
position (Figure 4-1 and 4-2).  Attach the sensor bulb using two zip ties.  
Insulate the bulb and expansion valve thoroughly with insulation (Figure 4-
3).  
						

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Figure 4-1 
 
Figure 4-2 
 
Figure 4-3 
  
						

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4.6  Compressor Maintenance Procedures 
 
A. General 
 
The following procedure is used whenever the compressor is replaced or 
contamination is suspected. 
 
B. Tools and Equipment 
Designation Ref. No. Qty Remarks 
None - - None 
 
C. Compressor Replacement 
 
Flush system and replace compressor per the Refrigerant Servicing section.  
						

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5.0 TROUBLESHOOTING 
 
5.1 General 
 
The procedures below present troubleshooting charts for the air conditioning 
system and the compressor.  A diagnoses chart is presented for insufficient air 
conditioning system cooling.  The performance characteristics of an aircrafts 
particular system are dependent upon the design parameters of the systems 
components.  The performance of any one particular system varies with ambient 
temperature and humidity.  The information below presents possible air 
conditioning system problems and solutions. 
 
CAUTION:  Do not operate air conditioning system with condenser air outlet 
blocked. 
 
5.2  Air Conditioning System Diagnosis Chart 
 
Figure 3 shows a procedure for diagnosing air conditioning system problems.  
Following this procedure will expedite the troubleshooting process.  
						

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Figure 3.  Air Conditioning System Diagnosis Chart  
						

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5.3  Air Conditioning System Troubleshooting 
 
 
 CONDITION  
SERVICE PRESSURE 
GAUGE READING  
 PROBABLE CAUSE  
CORRECTIVE ACTION 
INSUFFICIENT 
REFRIGERANT 
CHARGE 
 
Insufficient cooling.  
Bubbles appear in sight 
glass (if so equipped).   SUCTION  
PRESSURE:  below 
normal 
 
DISCHARGE 
PRESSURE:  below 
normal Refrigerant is low, or leaking 
a little. 1.  Leak test. 
2.  Repair leak. 
3.  Charge system. 
 
Evacuate as necessary 
and recharge system. 
ALMOST NO 
REFRIGERANT 
 
No cooling action.  A lot 
of bubbles or something 
like mist appears in sight 
glass (if so equipped). SUCTION  
PRESSURE:  much 
below normal 
 
DISCHARGE 
PRESSURE:  much  
below normal Serious refrigerant leak.  Stop compressor 
immediately. 
 
1. Leak test. 
2. Discharge system. 
3. Repair Leak(s). 
4. Replace receiver drier, 
if necessary. 
5. Check oil level. 
6. Evacuate and recharge 
system. 
FAULTY EXPANSION 
VALVE 
 
a) Slight cooling. 
Sweating or frosted 
expansion valve outlet. 
 
 
 
 
 
b) Insufficient cooling. 
Sweated suction line. 
 
 
 
 
 
 
 
c) No cooling. 
Sweating or frosted 
suction line.  
 
 
a) SUCTION  
PRESSURE:  below 
normal 
 
DISCHARGE 
PRESSURE:  below 
normal 
 
b) SUCTION  
PRESSURE:  above 
normal 
 
DISCHARGE 
PRESSURE:  above 
normal 
 
 
c) SUCTION  
PRESSURE: above 
normal 
DISCHARGE 
PRESSURE: below 
normal  
 
 
a) Expansion valve restricts 
 refrigerant.  Or, expansion 
valve is clogged.  Or, 
expansion valve is 
inoperative.  Or, valve stuck 
closed.  Thermal bulb has 
lost charge. 
 
b) Expansion valve allows  
too much refrigerant through 
evaporator. 
 
Sensing bulb on suction line 
not well insulated or properly 
attached to line. 
 
 
c) Faulty expansion valve.  
 
 
a) 
1.  Discharge system. 
2.  Replace valve. 
3.  Evacuate and recharge 
system. 
 
 
 
b) 
1. Check valve for 
operation.  If suction side 
does not show a pressure 
decrease, replace valve. 
2. Check security and 
insulation on sensing bulb. 
 
 
c) 
1.  Discharge system. 
2.  Replace valve. 
3.  Evacuate and recharge 
system. 
  
						

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 CONDITION  
SERVICE PRESSURE 
GAUGE READING  
 PROBABLE CAUSE  
CORRECTIVE ACTION 
AIR IN SYSTEM 
 
Insufficient cooling.  
 
Sight glass (if so 
equipped) shows 
occasional bubbles.   SUCTION  
PRESSURE:  above 
normal 
 
DISCHARGE 
PRESSURE:  above 
normal Air mixed with refrigerant in 
system. 1. Discharge system. 
2. Replace receiver drier. 
3. Evacuate and charge 
system. 
 
MOISTURE IN SYSTEM 
 
After operation for a 
while, pressure on 
suction side may show 
vacuum pressure 
reading.  During this 
condition, discharge air 
will be warm.  As 
warning of this, reading 
shows approx 6 psi 
oscillation. SUCTION  
PRESSURE:  below 
normal 
 
 
DISCHARGE 
PRESSURE:  above 
normal Drier is saturated with 
moisture.  Moisture has 
frozen at expansion valve.  
Refrigerant flow is restricted. 1. Discharge system. 
2. Replace receiver drier 
 (twice if necessary). 
3. Evacuate system  
completely.  (Repeat 30 
minute evacuating three 
times.) 
4. Recharge system. 
 
FAULTY CONDENSER 
 
Insufficient cooling. 
 
Bubbles appear in sight 
glass of drier. 
 
Suction line is very hot. 
 
 
 SUCTION  
PRESSURE:  above 
normal 
 
 
DISCHARGE 
PRESSURE:  above 
normal Condenser air or refrigerant 
flow is restricted. Check condenser for dirt 
accumulation. 
 
Check for refrigerant 
overcharge. 
 
If pressure remains high in 
spite of all above actions 
taken, remove and inspect 
the condenser for possible 
oil clogging. 
 
HIGH PRESSURE LINE 
BLOCKED 
 
Insufficient cooling.  
 
Frosted high pressure 
liquid line.   SUCTION  
PRESSURE: much  
below normal 
 
DISCHARGE 
PRESSURE:  much 
above normal Drier clogged, or restriction 
in high pressure line. 1. Discharge system. 
2. Remove receiver drier 
and replace it. 
3. Evacuate and charge 
system.