Retrofit a cooler from R-502 to R-134a

I am not sure about that oil. I have an old car that I retrofitted the ac. I was told to be sure to purge the entire system and to use the 134a refrierant that had the oil in it so that you get the right amount as well. If you get to little it will not lubricate well and you will burnup the compressor. Too much and it will not cool well. Also be sure to put a NEW filter on the system. Please note that some manufactures call the filter different names. Also it would be a good idea to change the control valve. That is a small inexpensive valve that is the cause of more failures. When it is working it will not kick the compressor in should you not have the correct pressure (caused by a small leak).

Hi a couple of points arrise first due to the different evaporating temperature of R502 and R134a you are going to lose a lot of duty, the compressor may not be suitable for R134a and could suffer damage due to excessive head / valve plate temperature or hydrulic du to flood back.

Regards the oil POE is fine with R134a and R502 but you cannot use mineral oil with R134a, before retro fitting with R134a you must carry out sufficient oil changes using POE until the mineral oil content is<5%

Instead of R134a consider R404a, you will still need to do the oil change procedure and will end up with system operating criteria closer to R502

POE is the correct oil for your application. Please identify which compressor is being used in this so I can verify its compatibility with R134A. The TXV should be replaced as the orifice size needs correction for R-134A refrigerant and if the temperature of the evaporator is going to be different. Typically a low temperature R-502 compressor will operate efficiently in a high temperature R-134A application. As a previous post stated if low temperature application R-404A is a better selection than R-134A.

R-502 and R-134a are two radically different refrigerants in regards to their applications.

R-502 was a low temperature refrigerant, now usually replaced by R-404a.

R-134a is the replacement for R-12 a medium to high temperature refrigerant.

The compression ratios for the two are very different as well as discharge and suction pressures. Very few compressors are able to handle this range of refrigerants.

Oil:

(ABO) Alkylbenzenes was for the old refrigerant's and the temporary replacements.

(POE) Polyol-esters are for the new hydroflorocarbon refrigerants. It is totally compatible with all other refrigerants.

Other notes:

Refrigeration metering devices:

A change in refrigerants will require a change in the method of metering the flow of refrigerant. You will have to change either the thermal expansion valve, capillary tube, piston, etc., device in order to match the refrigerant application.

At this point in time it is more probably more cost effective to just replace the equipment as refrigerant change outs have historically no guaranteed record of performance.

R-134a performs well @ evaporator temperatures of 20 degF and above. R-502 is a low evaporator temperarture refrigerant (-40 degF to 10 degF). The best long term options for R-502 are the HFC's (R-507A, or R-404A). Both require POE oil. If the equipment is very difficult to flush (complex piping circuits), an interim replacement for R-502, such as R-408A can be used. R-408A will accept Alkylbenzene oil, thereby avoiding the oil charge retrofit. R-408A is more efficient than R-502 and will require a smaller capacity metering device. The most popular long term retrofit seems to be R-404A which is a blend with a small glide. R-507A on the other hand, is an Azeotrope (no glide) and has a higher efficiency than R-404A. Go figure. Call your local refrigeration wholesaler, or check out refrigerant manufacture websites (Honeywell, Dupont, Atofina, ICI, ICOR) for specific instructions. Good Luck.

I miss R-502: simple, prdictable and a true azeotrope. Your correct in that R-507 gets the short end of the stick. Poor marketing perhaps. That said I believe that R-507 is considerd as a near azeotrope due to its blend.