[Supras] R134a pressure switch; buying refrigerant

[berniek@technicaldevelop.com]

Jim:

    At least as of last year it was not illegal to vent R134a to the atmosphere, as it is not a clorofluorocarbon as R12 is.  Beyond that, the temperatures and pressures are different for R134a than for R12.  It may be that your pressure switch is OK, but you may really need one for R134a.  Its been a long time since I looked at this, and stocked up on LOTS of R12 instead of pursuing R134a, having a few old cars.  But you can find the information at a refrigerant manufacturer's website, like Forane.  You want the pressure-temperature charts for both.  

    A quick check of ebay shows that R134a is sold without need of an EPA license, not true of R12.  The commercial establishments like Grainger do sell only to "licensed commercial establishments".  

    If you ever need to get a license to buy refrigerant, you can buy any one (including R-22 for home use) with just the lowest level license, available by correspondence test over the internet from epatest.com.  You can download a study guide first, free.  This license will entitle you to work commercially on car systems, but not fixed systems, for which a proctored test is required.

    In the short term, you could also get an O-ring sealed tubing piercing valve, and plumb it to a new pressure switch before installing it.  A potential problem is that they may not be made in metric sizes.  A quick check on the internet will tell you this.  There are one or two very big refrigeration supply houses on the first page or two, if I recall correctly.  One other problem with piercing valves is that the leak over the long term.  

    If you vent the system slowly so as not to lose oil, you can change the pressure switch quickly  so as not to get air into the system.  Just be all ready to do so first.  Doing this will avoid the need of pulling the system down with a vacuum pump.  When refilling it, you can get by with just a low side gauge, or a "recharge" kit although a complete high and low side gauge kit is best (again check ebay).  I'm sure you are aware of this, but gauge port fittings for R12 and R134a are different.  Set the system to maximum cool, and add R134a into the suction port just to the point where bubbles in the dryer sight glass disappear, then add maybe 2-3 ounces more.  You can turn the container upside down to liquid charge, but be VERY careful with charging rate to avoid sucking liquid refrigerant into the compressor.  


    Hope this helps.


                BernieK