Mixing R-143a PAG and Ester oils

Masospaghetti wrote:
> Steve wrote:
>
>> Masospaghetti wrote:
>>
>>> Sorry for three posts in a row. Just got finished under the hood and
>>> its been awhile.
>>>
>>> Napa dude says they will mix fine and that they're actually "the same
>>> thing". I have Ester in the system now, its been retrofitted. Its a
>>> 1985 Corolla. Only reason i'm asking is because those e-z charge
>>> bottles with the press top come with oil in them and only come with
>>> PAG. (my system leaks slowly so it'd be more convienent for me)
>>>
>>> Thanks
>>
>>
>>
>>
>> They ARE NOT the same thing. They are chemically different. Ester oil
>> is a slightly poorer lubricant than PAG, but PAG is highly reactive
>> with any trace of chlorine left over from when the system was running
>> R-12. Newer PAG oils labelled "double-end-capped" are chemically
>> stabilized so they won't react with chlorine, and are sold as being
>> fully compatible with R-12. I'm not sure I trust the chemical
>> stabilization process over the long haul, but that's just me. In a
>> retrofitted system, I would always gravitate toward sticking with
>> ester oil, simply because I *know* it won't break down from chlorine
>> contamination. Even though its not as good an oil as PAG I figure
>> non-degraded ester beats the heck out of PAG that's turned to brown
>> grittyt mud due to reaction with chlorine residues from R-12.
>>
>> The oils are compatible with each other and both are compatible with
>> R-134, so oil circulation won't be the problem. IF there is any
>> problem, it will be one of two things- breakdown of the PAG due to
>> reaction with chlorine, OR a problem I haven't mentioned yet:
>>
>> ALL R-134a oils (PAG and POE aka 'ester') are extremely hygroscopic
>> and absorb water from the air very quickly. They come with a little
>> water already absorbed, no matter how good the packaging. When you
>> open the cap to add some oil, they absorb a little humidity before you
>> can close it again. Even the "oil charge" cans have traces of water in
>> the oil inside absorbed in the factory where its packaged. Every time
>> you add a little oil to an R-134a system, you ARE adding a little
>> water. Over time continually adding oil to a leaky R-134a system will
>> put in enough water to overwhelm the dessicant in the drier, and when
>> that happens acids will start forming in the system and you'll
>> ultimately have oil breakdown and compressor failure.
>>
>> Short version: fix the leak.
>>
>>
>>
> Thanks for the info.
>
> How will I know when I need to add more oil? I've had to add about 4
> ounces of straight refrigerant in the past six months or so but I
> haven't added any oil yet.

At best its a guessing game. The last time I tried to estimate how much
oil to add over time, I underestimated and wound up with a dry (and
seized) compressor in addition to the evaporator core that was leaking
in the first place. Thats why I say just fix the leak.