Automotive Air Conditioning Information Forum (Archives)

TRB on Mon August 11, 2003 10:49 AM

Minimum requirements for converting a system to R134a.

If system has any refrigerant R12 left in the system it must be reclaimed by an approved recovery machine.

Accumulator/drier must be replaced with an R134a compatible replacement. Conversion fittings and label must be added to the system. Label should have the amount of R134a used and quantity and oil type listed. If vehicle is not equipped with a high pressure cut off switch it must be added. That is the required minimum! While complying with the EPA laws may not provide the best performance.

Flushing the system to remove the mineral oil and debris should also be done. R134a and mineral oil do not work well together so leaving it in the system with R134a is not recommended! O-rings should be replaced with either NBR or HNBR replacements. Adjustment of the pressure cycling switch may also be needed to achieve the best performance. In some cases an upgrade of the condenser may be required to achieve the original performance. In many cases the parallel flow condenser will not be available as a direct replacement. Using a universal parallel flow is an option. A new custom hose set would be needed for the different style fittings used on the various parallel flow condensers.

There are many different suggestions when charging a R12 system with R134a. System must be evacuated before starting the charging procedure. I suggest you start with about 70 percent of the original R12 charge and add an ounce at a time until vent and pressure readings reach the best available results. Remember it is easy to over charge a system with R134a so patience is important.


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Edited: Sat September 27, 2014 at 12:59 PM by TRB

ice-n-tropics on Tue May 20, 2014 9:08 AM

Might recheck the recommendation for NBR elastomers because I've seen split NBR O-rings that absorb R-134a as a liquid and when the pressure is suddenly reduced the absorbed refrigerant changes state to a gas and quickly expands splitting the ring along the molding parting line.
hotrodac

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Isentropic Efficiency=Ratio of Theoretical Compression Energy/Actual Energy.
AMAZON.com: How To Air Condition Your Hot Rod

wptski on Tue May 20, 2014 12:38 PM

Quote
Originally posted by: ice-n-tropics
Might recheck the recommendation for NBR elastomers because I've seen split NBR O-rings that absorb R-134a as a liquid and when the pressure is suddenly reduced the absorbed refrigerant changes state to a gas and quickly expands splitting the ring along the molding parting line.

hotrodac
A split ring that's splitting??? I'm confused!

ice-n-tropics on Tue May 20, 2014 7:00 PM

Your a senior member with lots of smarts so I'll explain this in detail, one time.
An o-ring is molded in a 2 sided mold. each mold half is a half hemisphere so that the round cross section o-ring can be ejected from the mold with out undercuts. The mold parting line usually leaves flashing which is minimized by a post molding tumbling process. The expansive internal force of expanding absorbed refrigerant separates/cracks the o-ring at the weakest point which is the mold parting line.
hotrodac

-------------------------
Isentropic Efficiency=Ratio of Theoretical Compression Energy/Actual Energy.
AMAZON.com: How To Air Condition Your Hot Rod

wptski on Tue May 20, 2014 10:33 PM

Maybe its an "O" ring brand problem. I use core tools and just went through an issue. I was sent some new "O" rings and quickly found out that the old ones had swelled. I have read that it's normal caused by exposure to refrigerant and oil. I had asked them what their "O" rings were but they couldn't answer that. My problem was first blamed on using a Heptane based cleaner on the CRT. NBR and HNBR are both compatible with Heptane.