R134a refrigerant amounts being critical

[Cusser]

I have a question after reading several times that R134a refrigerant amount is more critical than such had been in the R-12 days.

Is it that modern AC receiver-driers have smaller capacity to save manufacturers when adding R134a, and that's why the R134a amount is so critical? It seems that as long as liquid refrigerant is pushed forward to the expansion valve then the level of liquid refrigerant in the receiver-drier can be a few inches/few ounces additional?

I was just wondering....see somewhat related topic for my 1998 Frontier also posted today https://autoacforum.com/viewtopic.php?f=3&t=14612

[tbirdtbird]

Most systems today are CCOT thus have an accumulator as you know.
I believe the critical charge has something to do with that. No longer a reserve in the non-existent FD

I have long wondered why you couldn't have both (custom) , but that question has never come up.

[Tim]

Most systems today are CCOT thus have an accumulator as you know.

Many newer vehicles are going with a condenser-mounted drier.

[Cusser]

My 1998 and 2004 Frontiers both have condenser-mounted driers (2004 shown).

[DetroitAC]

Systems are smaller in refrigerant charge than they used to be, meaning a 2022 model sedan will have much less charge than a 1996 model. Seals and hoses are generally better so the "reserve" amount is usually 100 to 150g (4 to 6 oz) older systems were 8oz or more.

So, are they more sensitive? I guess so, personally seems to me like it's still a pretty big window of good performance, not that hard to hit when the total charge is 600g, and 450g performs just fine.

[tbirdtbird]

Those numbers lookin' good, Cusser

[Cusser]

Those numbers lookin' good, Cusser

Thanks. Funny how my 1998 and 2004 Frontiers share same engine, transmission, and AC, and the 1998 compressor is running strong at 267K miles (yes, I removed a compressor shim a few years ago to solve a slipping issue) and yet the 2004 AC compressor seized at about 107K miles.

Yes, the 2004 got a new condenser, drier, compressor, and I backflushed the high pressure lines....

Both these Frontiers do great AC in the Arizona desert, I must say !!!