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GRANT LAIDLAW
Grant Laidlaw is currently the owner of the Air Conditioning and Refrigeration Academy ( ACRA ) in Edenvale . He holds a Bachelor of Business Administration and an associate degree in educational administration . He has a National Technical Diploma and completed an apprenticeship with Transnet . He has dual-trades status : refrigeration and electrical . He has been involved with SAIRAC for 17 years and has been a Johannesburg committee member for the past eight ( chairman in 2011 and 2012 ). Currently he is the treasurer ( Johannesburg council ) as well as president ( national council ).
CHEST FREEZERS - MAINTENANCE ESSENTIALS
By Grant Laidlaw
Freezer maintenance too should include replacement of the drier that could fail disastrously .
Chris asks : Grant , we have just seen a refrigerant drier quite literally explode . A technician was working on a chest freezer when this happened , really quite a bang ! Any advice ? Are people aware of this ?
Hi Chris . Well yes , some people do know about this and given the fact that you did not mention fire being part of this particular incident I assume that the freezer in question was an older model utilising R134a , or a really older model utilising R12 . If this had been a newer model utilising R600a ( a flammable hydro carbon ) things would have been somewhat more interesting .
Let me paint a picture : A chest freezer compressor becomes faulty . A technician replaces the compressor , recharges the system and invoices the customer . Job done – but , in this scenario , the drier was not replaced , vacuum was not drawn and no nitrogen was used when brazing the joints .
Moisture has entered the system , oxidation occurred inside the system when the pipes where joined and the drier may have
been already saturated . The moisture circulates through the system forming a droplet which passes through the saturated drier and enters the capillary tube . As the droplet reaches the end of the capillary tube it is exposed to the below freezing evaporator temperature and freezes , blocking the capillary tube .
The compressor now begins to draw higher amperage as the high-side pressures climb due to the blockage . As the electrical current increases , the overload protection is activated and cuts the power to the compressor . The overload resets after a few minutes and power is restored to the compressor . The start winding attempts to start the compressor but the very high pressure at the outlet remains , preventing the compressor from starting . High amperage again trips the overload . This very damaging cycle is then repeated and the compressor start winding fails .
The worried owner notices the increase in temperature and this time calls you : “ Chris , my freezer made funny noises and is now getting warmer , it ' s still freezing but something is wrong .”
You attend to the call-out , and on testing the compressor , discover the burnt-out winding . As luck would have it you just happen to have a replacement with you . Great . You put your piercing pliers on the process tube and discover that there is no refrigerant pressure . A Leak ? Next , let ' s begin the job by removing the old drier . Tools are ready , you light up your oxy-acetylene torch and apply heat to the drier ' s connection .
But wait , there was no leak . All of the refrigerant has been pumped into the condenser and that drier you are about to heat up is full of high pressure liquid refrigerant . Any heat applied will increase the pressure to the point when the drier will violently rupture ( explode ) expelling its contents , possible copper fragments , and in the case of hydrocarbons , burning liquid refrigerant in all directions including to where you are at that moment . There is no doubt that you will not be very happy at this point .
So , the moral : Always take a pipe cutter or a side cutter and safely , away from any ignition source , in a well-ventilated area , puncture a hole in a pencil drier before attempting removal . That ' s it – simple .
I must add that it is good practice to always replace the drier when replacing a compressor and draw a vacuum to remove moisture and non-condensables ( air ) from the system . Using nitrogen when brazing refrigeration pipes prevents oxidisation and carbon formation in the system which in turn may cause issues including blockages .
Thanks for the question Chris , I hope nobody got injured ! RACA
REFERENCES : 1 . ACRA
www . hvacronline . co . za RACA Journal I March 2021 39