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