Automotive Air Conditioning Information Forum

Hi Everyone,

I'm finishing up a head gasket replacement on my truck and decided to fix the ac. Years ago, a battery cell leaked acid on one of the refrigerant lines (didn't realize this had happened until I tore the motor down).

I bought a replacement line, a new receiver/dryer, expansion valve, and o-rings. I am also going to flush the system and replace the compressor. The thing I'm stuck on is the OEM replacement compressor (Denso) apparently comes pre-filled with ND-6 mineral oil. As I understand it, this oil is compatible with R12, but not R134 refrigerant. I'm fairly certain the system was converted to run R134 (adapters were placed on the service ports before I bought the truck).

My question is: can I drain the oil and flush it a couple times with PAG, then fill it? Most of the aftermarket brands say it comes pre-filled with "OEM-specified oil," but don't say what kind, so I'm assuming it's also ND-6. The Valeo comes "dry," but I've read a lot of less than favorable reviews about their compressors. I'd prefer to go with the OE manufacturer, but just don't know what to do and only want to do this once.

TIA for any advice - I've been unable to find much info online so far.

Although Toyota began converting to R-134a late in model year 1993, your '93 Pickup used R-12 and ND-6 mineral oil, according to the documentation I have.

I think you're right to presume that your truck was converted to R-134a sometime in its past based on the fittings on the service ports. Do you also see a sticker, usually placed near the compressor, the R/D, or on the radiator support indicating how much R-134a and PAG-46 (ND-8) were used at that time?

Regardless, I think your plan is a good one: Drain the oil that the compressor came with, rotate the mainshaft several times while tipping the compressor in different directions to ensure that you get out as much of the ND-6 as possible. Then flush it several times by filling it with PAG-46 and repeating the above process, thereby removing all the remaining mineral oil.

You didn't mention the condenser, but the system will probably cool better using R-134a if you replace the original serpentine condenser with a parallel-flow type.

For reference, the original specifications that I have for your truck are as follows: 29 ounces net weight of R-12, and 7.0 fluid ounces of ND-6 mineral oil. Right...Denso is OE for your truck.

seanzthekid wrote: ↑Sat Jul 06, 2024 10:27 pm the OEM replacement compressor (Denso) apparently comes pre-filled with ND-6 mineral oil. As I understand it, this oil is compatible with R12, but not R134 refrigerant.

My question is: can I drain the oil and flush it a couple times with PAG, then fill it?

TIA for any advice - I've been unable to find much info online so far.

I say YES !!!

I had the OPPOSITE situation a decade or so ago when I bought a brand-new compressor for my 1988 Mazda truck from the board sponsor (Tim had quite a time finding it brand-new too). My truck was staying R-12. I worked in a chemistry lab, and took a drop of the new compressor's oil in to work and tested it in 3 minutes (used an instrument called FTIR) which identified it as a PAG oil. So I drained the PAG oil out, added a few ounces of new R-12 525 mineral type oil, rotated the compressor drive plate about 10 times by hand, then dumped that oil. Then I flushed again with a few ounces of new R-12 525 mineral type oil, rotated and drained that again. I don't remember if I did a 3rd flush, but after draining I added the appropriate amount of new R-12 525 mineral type oil and installed the compressor. It's still working.

Funny, a couple of months later a co-worker asked for my help to install a new compressor into his 1990 Mazda Protege (also keeping R-12), and he also bought his compressor from Tim/AMA, and we tested its oil too, and HIS compressor came with R-12 525 mineral type oil, go figure !!!