[Supras] Refrigeration service

[berniek at technicaldevelop.com]

PS:  Under NO circumstances is any of the mineral oil used as a compressor lubricant used in R-12 systems to be left in the system if an R-134a conversion is done.  It is not easy to remove all of the mineral oil, since it circulates in the system with the refrigerant.  Mineral oil is NOT soluble in R-134a, not a good happening since the compressor requires oil mist circulation, with most of the oil in the compressor sump.  The popular conversion kits that say the mineral oil "goes to a place in the system where it will not be harmful" is bogus.  It winds up in the evaporator, the cooling chamber, where it reduces active surface area and thus cooling capacity.  There is no really good reason to convert to R134a.  Some hoses have to be changed because they are 134a permeable (smaller molecular structure of 134a than R-12).  Getting all of the mineral oil out of the system correctly requires disassembly, and flushing out the condenser, evaporator, compressor, etc,. before installing so-called polyalkaline glycol (PAG) or polyester oils which are R134a compatible.  

            BernieK
  ----- Original Message ----- 
  From: berniek at technicaldevelop.com 
  To: jdc25180 at cmsu2.cmsu.edu 
  Cc: Supras at supras.com 
  Sent: Thursday, March 01, 2007 10:41 PM
  Subject: Re: Refrigeration service


  Darren and list:

      Refrigeration service is not difficult or mysterious once the fundamentals are understood.  Take some alcohol on your hand, blow on it to make it evaporate, and your hand gets cold.  Refrigerant works in a similar way.  You evaporate a liquid in the system by dropping the pressure through a valve which allows expansion (the expansion valve), and the so-called "latent heat of vaporization" drives down the temperature, since the liquid boils at a lower temperature once the pressure is let down through the expansion valve.  You then compress the vapor, cool it in the condenser to liquify it (like condensing steam to water from a teakettle on the back of a spoon) and evaporate it again.  The cycle repeats.  

      If you have a vacuum pump and bell jar, you can place a cup of water in the belljar and make it boil at room temperature once you lower the pressure by pulling a vacuum.  Refrigerant works the same way but at a higher pressure, to pull heat out of the evaporator by boiling at a much lower temperature than water does.  Latent heat of vaporization of water pulls heat out of a pot of boiling water, so the temperature cannot get above 212F (at sea level), but refrigerant does the same thing at a much lower temperature as stated.  If you turn up the heat under a pot of water, it will boil away faster, but the temperature does not increase.  

      There are several classes of refrigeration technician licenses.  As of about 18 months ago, you could study and take the exam over the internet for car service, which interestingly enough will let you buy all refrigerants, even those used in fixed applications.  The site to go to for that is www.epatest.com.

      You wil then need a vacuum pump, gauge set to read high and low side pressures (suction and discharge of the compressor) and miscellaneous accessories like an oil injector.  It will cost a few hundred dollars, but these are tools you will have all of your life.  Just so you know, R-12 and R-134a take different hose end fittings.  If the EPA has not changed the rules, you can also buy R-22 to recharge your home air conditioner, even window types.  I've done a couple of those, using charging fittings and small copper tubing soldered into a hole punched in the copper suction line of the compressor.  The fittings and such are available on the internet of from Grainger.  

      One consideration:  NEVER let moisture into the system.  Once it is opened, it should be capped off.  If you are charging a system from scratch, you will need to pull a deep vacuum to get all of the water vapor (and any residual air) out of the system.  You are supposed to recover refrigerant according to EPS rules, but I don't think the refrigeration police are going to come to your garage.  Technically, you can recover used refrigerant in a propane cylinder as long as it is painted the right color and has the right fittings.  If fact, the on-line license test is mostly about rules such as that.  

      One look on ebay shows that the price of R-12 is coming down.  Wish I'd sold some of mine when the price was higher.  Legally, you do need at least the on-line license to buy the stuff.  

              BernieK