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!