The compressor oil circulates through the entire a/c system via refrigerant.
Therefore, if you are converting to R134a, you will be forced to use different oil spec from R12 mineral oil and thus, better to use new R134a compressor filled with proper oil designed for R134a usage.
By the way, this is the reason why you should disable your compressor if your refrigerant level is very low.
The oil can't return to the suction port of the compressor and thus, low oil level yet the compressor keeps spinning despite the triple pressure switch that meant to disable the compressor at extremely high/low pressure condition.
It will only disable the compressor when the refrigerant is really low but by that time, it could be too late.
Recently, one UK owner contacted me with his a/c issue and his system only had 140g left in the system yet the compressor kept engaging.
Glad he reacted early enough before splashing metal flakes from the compressor.
He now has good a/c again.
If you want the OEM R134a compressor, go for the P9K spec. Parts #38810-P9K-E01
Manufactured by Denso and shared among several Honda models.
Much quieter and improved friction loss than the original R134a compressor fitted to earlier models.
This is the one I used for my A/C Refresh.
It is much more expensive than the aftermarket one and it does not
come with the new pulley/clutch/pressure plate/field coil so you must re-use your existing one (if it's not the cause of your noise) or get new assy.
If going for the aftermarket one, since OEM is by Denso, I don't see the point of selecting other brands.
Denso compressor is one of the most reliable and durable model out on the market.
One of the benefit of going for the aftermarket compressor is that you will get not only the compressor body but also the pulley/clutch/pressure plate/field coil included at significantly cheaper price than the OEM P9K one.
Remember, P9K is only the compressor body and those are not included.
Please note that the information on densoautoparts.com is not correct for some of the year models (mainly for the geometry offset of the compressor bracket and the pulley from 97+ models) so please be careful when selecting the aftermarket compressor.
Here in UK, I know several owners bought Denso compressor #471-1193
Please note that I never installed these two aftermarket models by myself so I can't confirm the following information based on my own experience.
The difference between the two models seemed to be only the pulley/clutch area (diameter/offset) and the compressor body itself seemed to be the same.
is for the R134a up to 96 NSX.
However, for some reason, Denso fitted smaller diameter pulley/clutch (about 125mm) for this -1194 that you may need to find alternative smaller a/c belt.
Without it, you may not be able to achieve the ideal belt tension with the existing adjuster.
Not a problem if you are planning to transfer your existing pulley/clutch/pressure plate/field coil on this new compressor.
is for the R134a on 97+ NSX although densoautoparts website doesn't show it like that.
Honda modified the design of compressor bracket attached to the eng block for 97+ MT/AT models.
This will shift the compressor body towards the right wheel yet the crank pulley and idle pulley position didn't change.
In order to compensate for the changes in geometry, Honda also changed the offset of the pulley/clutch on OEM compressor.
With -1193, it will have the correct pulley offset when used together with 97+ bracket.
Also, it comes with larger diameter pulley (and thus, can use existing belt/adjuster) of about 140mm compared to -1194.
Again, you could use this one if you are planning to transfer your existing pulley/clutch/pressure plate/field coil on this compressor.
Or, if you have aftermarket header and want to shift the compressor body away from the front header (but the difference is very small that it may not worth it unless you can find used bracket), then you can use this compressor without transferring your existing pulley assy and just replace the bracket to the 97+ spec although the new one is fairly expensive (for the price, you can buy another new aftermarket compressor….).
What goldnsx mentioned is this;
When you get the new compressor, it will be delivered like this.
(Please note that this is OEM Denso P9K compressor so it doesn't include the pulley assy. With the aftermarket Denso one, it does.)
The yellow marked parts is the shipping plate.
When you remove your existing compressor, it will look like this.
The blue marked parts is the service plate/valve.
Mine is R134a from the factory so the label and appearance (safety valve) would be different from your R12 one but the idea is the same.
So, as you can see, before you install the new compressor, you must swap the yellow and blue parts.
Please note that under the service plate, there is an octagonal shape seal.
You must install new one on the new compressor.
With the aftermarket Denso compressor, you should find new one in the bag inside the box.
However, with OEM P9K one, it doesn't include it so please get it (38839-PR7-A01) in advance.
Not expensive any way and you can find aftermarket one as well.
The PAG oil used on R134a system absorb moisture really quickly so same for the drier, deal with it at the very last moment just before the evacuation of the system.