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Do's & Don'ts - 2008 1
Good Servicing Practices
Do’s & Don’ts
Do's & Don'ts - 2008 2
Areas of Focus
• Brazing
• Cleaning and Flushing
• Leak Testing
• Evacuation
• Measurement / holding of vacuum
• Charging of Refrigerant
Do's & Don'ts - 2008 3
Essentials of Brazing
• Melts at temperature lower than that of base metals
• Rod should melt by contact with heated base metal
• Melted Rod Material flows into clearance between walls of the two tubes through capillary action
Brazing Filler Rod
Torch
Base Metal
Brazing Filler Rod
Do's & Don'ts - 2008 4
Good Brazed Joints: Prerequisites
Right techniqueRight temperature
Right Joint preparation
• Surface preparation
• Joint clearances
Right brazing alloys; Right Flux
Do's & Don'ts - 2008 5
Suitability of Brazing Equipment
• Oxy Acetylene: Best suited
• Oxygen-LPG: Better suited than Air-LPG
• Air-LPG: May be inadequate, but O.K. for Cu tubes up to 3/8” with Swirljet (or Cyclone) Torches
• Kerosene Blow-lamp:
Should be avoided
Do's & Don'ts - 2008 6
Cleaning and Flushing
USE .
• Dry Nitrogen
• Trichloroethylene
(for chemical cleaning)
(ensure trichloroethylene vapourises and does not remain as liquid after cleaning, by application of gentle heat)
DO NOT USE• CTC (Being phased out)
• Air (Contains moisture, lubricant & other gases, detrimental to the system)
• Oxygen – not O.K. for compressor oil
• Petrol (has a lot of impurities which can destroy the compressor)
Do's & Don'ts - 2008 7
Leak Testing
USE .
• Dry Nitrogen (after the system has been reassembled) Should have a dew
point of at least -400C
• Commercial nitrogen with a drier (to reduce moisture content)
DO NOT USE
• Compressed air
(Contains moisture, lubricant & other gases, detrimental to the system)
• Refrigerant
Do's & Don'ts - 2008 8
Dry Nitrogen
• Different types of N2 available
• For refrigeration service, following specification recommended : Purity : 99.995% Dew Point: -40 oC at least
• Approximate price:
Rs. 325/- per cylinder of 7 m3 (with security deposit ranging from Rs. 5000/- to Rs. 10,000/-)
• Makes: Bombay Oxygen, Inox & others
Do's & Don'ts - 2008 9
Equipment for Evacuation
DO NOT USE
• Refrigeration System’s compressor
• Other Hermetic / Semi Hermetic / Open Refrigeration compressors
May lead to compressor failure as:
moisture gets deposited in compressor’s discharge chamber
there can be loss of lubricant
Creates inadequate vacuum for moisture to boil and vacate the system
Do's & Don'ts - 2008 10
Why Vacuum Pump is needed
Temp
(OC) Microns (Hg)
mm (Hg)
Inches (Hg)
psia Millibar Pascals
100 760,000 760 0 14.7 1013 101,30070 233,680 234 -20.8 4.52 303 30.350 92,456 92 -26.36 1.79 12 12,00040 55,118 55 -27.83 1.07 72 7,20030 31,750 32 -28.75 0.61 45 4,50025 23,000 23 -29.1 0.44 30 3,00020 17,500 17.5 -29.3 0.34 23 2,30010 10,000 10 -29.65 0.196 13 1,3000 4,572 4.5 -29.82 0.088 6 600
Pressure
Do's & Don'ts - 2008 11
2 CFM Pump (1/4 HP)
3 CFM Pump (1/3 HP)
½ H
P C
ompr
esso
r
3.0
2.5
2.0
1.0
Vacuum in Microns of Hg10 100 1000 10,000 100,000 1,000,000
Comparison of Vacuum Pump vs Compressor
Do's & Don'ts - 2008 12
Equipment for Evacuation (Cont)
• Use specially designed vacuum pumps, capable of developing blank off pressure of 20 - 50 microns Hg
• Micron gauge capable of reading pressures in 5 - 5000 Microns range
Most preferred:
• Two stage, Rotary, multi-vane pump
Do's & Don'ts - 2008 13
Measuring Vacuum Accurately
• Use Pirani / Thermocouple vacuum gauge having a range from 5-5000/10000 microns
a. Evacuate to about 500 microns or lower
b. Isolate the vacuum pump & observe the rise in the vacuum for 5-10 minutes
c. Repeat (a) & (b) till the vacuum in (b) stabilises at around 1500 microns or lower. The lower the stabilised vacuum the better.
Do's & Don'ts - 2008 14
If Micron Level Vacuum Gauge is not Used
• If micron level vacuum gauges are not available Bourdon type vacuum gauges cannot read vacuum in
microns – hence actual vacuum reached cannot be known
In the absence of a micron vacuum gauge, the vacuum pump should be run at least half an hour after the Bourdon type vacuum gauge reading shows -30” / -760 mm / 0 millibar (at sea level).
Neither the vacuum level nor vacuum holding can be known from this. Therefore superior quality of evacuation & assurance using micron gauge will be absent in this case.
Do's & Don'ts - 2008 15
Charging
• Charge the same weight of refrigerant in the system, as recommended by the appliance manufacturer instead of charging by feel (To ensure good cooling performance and low energy consumption)
• Charging apparatus must provide for accurate weighing scales or calibrated charging cylinders (HFC-134a & HCs particularly are even more sensitive to charge quantity than CFC-12)
Do's & Don'ts - 2008 16
Use of Anti-Moist
Don’t Use Anti-Moist
• It has a harmful effect on compressor motor (Causes embrittlement of insulation leading to
premature motor failure)
• Strictly prohibited for HFC-134a systems
Instead, evacuate system properly and use the appropriate drier
Contamination &Cross Contamination
Contamination by : • Moisture• Non-condensables• Chemical residues• Dirt, dust metal particles• Organic contaminants
Cross-Contamination through:• Import of contaminants from other systems
or servicing equipment
Contaminants: • Other refrigerants, other lub. Oils, chemical
residues from other systems
Cross-Contamination due to Refrigerant Mixing
• Even at 10-20% of CFC-12 in HFC-134a & vice-versa, the azeotrope formed will have properties quite different from either
• This will seriously affect appliance performance
• Similar problems will arise with mixtures of CFC-12 & HCFC-22 or HCFC-22 & HFC-134a
• As full data on HCs / CFC-12 or HCs / HFC-134a mixing is not available, it is better to avoid their mixing.
CAUTION: Ensure that refrigerants do not mix.
AVOID.
Likely Sites for Refrigerant Cross-
Contamination
• Charging stills of E&C units, used for multiple refrigerants
• Recovery & R&R machines used for multiple refrigerants
• Recovery cylinders• Hoses & Manifolds• Old systems retrofitted with non-CFC
refrigerants
How to avoid Refrigerant Cross-Contamination
(Cont)• Ensure that all traces of the previous
refrigerants is removed from the charging still / recovery machine & the unit is evacuated to a deep vacuum (1000 microns) before switching to a new refrigerant
• If possible use separate E&C & Recovery machines for each type of refrigerants
• Use separate recovery cylinders for each refrigerant
Wrong Installation
Gap is less than 2”, after some
time wall will be
hot
Wrong v/s. right Installation
√
U Trap is must for drains
Wrong v/s. right Installation
X
Do's & Don'ts - 2008 24
LET US INSIST ON
GOOD SERVICE PRACTICES
WITH PHD .
THANKS!!
Do's & Don'ts - 2008 25
Contamination & Cross Contamination
Contamination by : • Moisture• Non-condensables• Chemical residues• Dirt, dust metal particles• Organic contaminants
Cross-Contamination through:• Import of contaminants from other systems or
servicing equipment
Contaminants: • Other refrigerants, other lub. Oils, chemical residues
from other systems
Do's & Don'ts - 2008 26
Cross-Contamination due to Refrigerant Mixing
• CFC-12 & HFC-134a when mixed, form high pressure azeotropes with pressure higher than either refrigerant
• Even at 10-20% of CFC-12 in HFC-134a & vice-versa, the azeotrope formed will have properties quite different from either
• This will seriously affect appliance performance
• Similar problems will arise with mixtures of CFC-12 & HCFC-22 or HCFC-22 & HFC-134a
• As full data on HCs / CFC-12 or HCs / HFC-134a mixing is not available, it is better to avoid their mixing.
CAUTION: Ensure that refrigerants do not mix
Do's & Don'ts - 2008 27
Cross-Contamination due to Refrigerant Mixing
Indicative Influence of Mixing of Refrigerants
0
25
50
75
100
125
150
0 25 50 75 100
% of CFC-12 in HFC-134a (by weight)
% o
f C
om
pre
sso
r d
isch
arge
pre
ssu
re
Do's & Don'ts - 2008 28
Likely Sites for Refrigerant Cross-Contamination
• Charging stills of E&C units, used for multiple refrigerants
• Recovery & R&R machines used for multiple refrigerants
• Recovery cylinders• Hoses & Manifolds• Old systems retrofitted with non-CFC
refrigerants
Do's & Don'ts - 2008 29
How to avoid Refrigerant Cross-Contamination (Cont)
• Ensure that all traces of the previous refrigerants is removed from the charging still / recovery machine & the unit is evacuated to a deep vacuum (1000 microns) before switching to a new refrigerant
• If possible use separate E&C & Recovery machines for each type of refrigerants
• Use separate recovery cylinders for each refrigerant
Do's & Don'ts - 2008 30
Common Practices• Use of blow lamp
• Brazing with Cu electrode for brazing Cu tubes Bundy/steel tubes
• Flushing with air / refrigerant
• Use of CTC / petrol for cleaning
• Leak testing using air/refrigerant
• Self-evacuation using system compressor or old / used compressor as vacuum pump
• Improper assessment of vacuum achieved
• Charging by feel (inaccurate)
• Use of anti moist
• Contamination / Cross Contamination of Refrigerants
Do's & Don'ts - 2008 31
Essentials of Brazing (Cont)
Melted Filler Rod material wets base metal and penetrates surface
& forms metallurgical bond.
Boundary locking layers (dotted) show metallurgical bond
Outer tube end (swaged)
Filler material
Spigot (inner tube)
Tube hollow
Do's & Don'ts - 2008 32
Temperatures for Brazing
Desired temperature range for Phos Cu Alloys
Average temperature for Phos Cu Alloys
Right temperature for Cu Ag alloys (Ag >35%)5900C
6000C
7050C
8150C