R12 Guage set on R134a?

[kmdigital]

Get a set of the proper gauges. They sell on ebay all the time for around $25-$35. Otherwise you need to use a T/P chart to determine what temps the system is seeing instead of being able to read it directly from the gauges. This can be done, but it is a nuisance. You can buy adapters on ebay also for around $10 to convert the older gauges to use with 134a, but then you still have the issue of oil contamination if you switch between different systems, so generally you are better off having different gauges for different systems.

 

[slowrev]

this would be comparison of pressure /temperature relationships between R12 and R 134a for those who care..


http://www.fjcinc.com/pdffiles/tprc.pdf

Are those pressures in the same system designed for r12? Or in seperate systems designed for the proper refrigerant ?

 

[grunewald]

My comparison of R12 and R134 as close to the same pressure/temp is my experience with other refrigerants, R22 , R410, and so on. Y'all are correct, R134 is a little higher than R12. I don't work on automotive a/c except my own. Do work on chillers with R22 and R134 up to 500 tons. Not too worried about oil contamination on systems this size, but small system, yes. Gauges are the same pressures, just the temp. scale for those pressures are different. I use two sets of gauges, for R22 and R134 because it is easier to see my refrig. temp. but the gauges are still 30 " to 120 psig.

 

[KICK]

Are those pressures in the same system designed for r12? Or in seperate systems designed for the proper refrigerant ?

134a was designed to replace/ not interchange with, the old R12. relatively the same pressure temperature relationship ,although on the hot end R134a has more pressure at a certtain temp, roughly comparable on low side

If I'm following what you are asking, you are missing the point of a pressure temperature chart for refrigerants.

what you want in an a/c system in a vehicle is to maintain an evaporator pressure just above the freezing point, and the metering device used in that a/c system was designed to maintain that evaporator pressure at a certain point.

that evaporator pressure has a corresponding temperature which you can read off the chart.

 

[dqdave1]

most important part of this question deals with the non compatibility of the oils in R12 and 134. Do not mix it. That means ; do not use same guages for both

 

[slowrev]

134a was designed to replace/ not interchange with, the old R12. relatively the same pressure temperature relationship ,although on the hot end R134a has more pressure at a certtain temp, roughly comparable on low side

If I'm following what you are asking, you are missing the point of a pressure temperature chart for refrigerants.

what you want in an a/c system in a vehicle is to maintain an evaporator pressure just above the freezing point, and the metering device used in that a/c system was designed to maintain that evaporator pressure at a certain point.

that evaporator pressure has a corresponding temperature which you can read off the chart.

No I am not missing the point on the pressure/temp chart. I was thinking of retrofitting R12 systems to R134. Does this pressure chart hold true in those cases ? And yes I know they are designed differently that was why I asked.

 

[normde2001]

Everything you need, low side gauge, freon, adapters, oil, and instructions is in the $30 r134a conversion kit at your local autoparts store. No need to worry about the high side pressure.

 

[KICK]

No I am not missing the point on the pressure/temp chart. I was thinking of retrofitting R12 systems to R134. Does this pressure chart hold true in those cases ? And yes I know they are designed differently that was why I asked.

I believe the reason the automotive industry settled on 134a was that it operated at similar temperatures and pressures, as compared to R12.

so if you do a retrofit, its a simple as cleaning up the old system and
changing the oil and fittings and adding the 134a.

the pressures obtained are relative to the operating conditions of the system, if everything is working properly you wont see much difference in the operating pressures between the two types of refrigerant.

if there is a low side problem with the metering device, whether its an orfice tube or a expansion valve, then the system wont run at the proper pressures. same holds for the condenser or high side..

all in all, changover is mostly invisible.

 

[greenedeere]

I also use the r-12 gages on the older cars, I always purge the lines before and after using the gages. I use a parts store r134 adapter to charge while watching the high pressure side and connect the low pressre hose between each can of r134 mostly for a feel good.As already said watch the two differant oils, the O rings should be changed if the system uses them, they are green in color, have found the older black ones have caused me some slow leaks,coat them in the proper oil before installing.R-134 is the best of the afforable replacements verses R-12 because all new and rebuilt compressors available are compatable with both,R-12 is harder to find and always cost more.All IMHO.