Do s & Don ts in Refrigeration & Air-Conditioning Servicing
Who is Better? OR
Common Practices that are damaging to the Refrigeration & Air-conditioning Systems Brazing with Cu electrode for brazing Cu tubes Bundy/steel tubes Flushing with air / refrigerant Use of CTC, 141b, 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) Contamination / Cross Contamination of Refrigerants
Areas of Focus Good Tools Tube Cutting, Deburring Flare fitting Swaging Bending Brazing Cleaning and Flushing Leak Testing Evacuation Measurement / holding of vacuum Charging of Refrigerant Cross contamination
Good Tools
Tube Cutting and deburring Pipe end shape of after cutting Deburring
Flare fitting Flaring Best?
Swaging
Bending Manual bending of pipe Bending by pipe bender
Essentials of Brazing Base Metal Brazing Filler Rod Melts at temperature lower than that of base metals Torch Rod should melt by contact with heated base metal Brazing Filler Rod Melted Rod Material flows into clearance between walls of the two tubes through capillary action
Essentials of Brazing Boundary locking layers (dotted) show metallurgical bond Filler material Spigot (inner tube) Tube hollow Outer tube end (swaged) Melted Filler Rod material wets base metal and penetrates surface & forms metallurgical bond.
Good Brazed Joints: Prerequisites Right Joint preparation Surface preparation Joint clearances Right brazing alloys; Right Flux Right temperature Right technique
Temperatures for Brazing 815 0 C Desired temperature range for Phos Cu Alloys 705 0 C Average temperature for Phos Cu Alloys 600 0 C 590 0 C Right temperature for Cu Ag alloys (Ag >35%)
Brazing by passing dry nitrogen
Brazing Good or Poor
Flame
Caution!! AVOID Objects even 450 mm away from the flame may get hot enough to cause ignition Keep all flammable material at least 2 meters away from the brazing zone
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 Cyclone or Powerjet Torches
Cleaning and Flushing USE Dry Nitrogen ODS free chemical for flushing (for chemical cleaning) DO NOT USE 141b (Going to be 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)
Leak Testing USE Dry Nitrogen (after the system has been reassembled) Should have a dew point of at least -40 0 C DO NOT USE Compressed air (Contains moisture, lubricant & other gases, detrimental to the system) Commercial nitrogen with a drier (to reduce moisture content) Refrigerant
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
Why a Vacuum Pump is needed?
Comparison of Vacuum Pump v/s Compressor
Equipment for Evacuation Use specially designed vacuum pumps, capable of developing blank off pressure of 20-50 microns Hg Most preferred: Micron gauge capable of reading pressures in 5-5000 Microns range Two stage, Rotary, multi-vane pump
Measuring Vacuum Accurately Use 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) stabilizes at around 1500 microns or lower.
Charging The best method of charging is charge by weight. Charge the same weight of refrigerant in the system, as recommended by the appliance manufacturer instead of charging by feel or back pressure. (To ensure good cooling performance and low energy consumption) Charging apparatus must provide for accurate weighing scales or calibrated charging cylinders
Contamination & Cross Contamination Contamination by : Moisture Non-condensable 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
Likely Sites for Refrigerant Cross-Contamination Charging stills of Evacuation & Charging (E&C) units, used for multiple refrigerants Recovery & Recycling machines used for multiple refrigerants Recovery cylinders Hoses & Manifolds
How to avoid Refrigerant Cross-Contamination 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 Evacuation & Charging (E&C) and Recovery machines for each type of refrigerants Use separate recovery cylinders for each refrigerant