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Hi, greenberet.
I think you got confused by the superseded parts no..
Until 1997, all NSX left the factory with PR7 spec compressor regardless of the R12 or R134a system used.
There are at least 3 different PR7 spec compressors available (one of them only used on certain VIN range of Type-R) and those are the ones used up to and including the 1996 models.
The P9K spec compressor was only introduced in 1997 for the NSX (together with the later spec bracket) and it superseded all of the previous PR7 R134a spec compressors apart from the R12 one, obviously.
So, if you just look up the parts system, the P9K compressor will be displayed for the pre-97 NSX that left the factory with the R134a gas.
As mentioned, the compressor body dimension is the same regardless of R12/R134a spec, PR7/P9K, year model, etc, etc.
You just need to keep the correct combination between the CL/Pulley and the Bracket.
Because the body dimension is the same, if the bracket shifted the compressor outward towards the RR wheel arch, you need to change something further, as you stated correctly that the crank pulley and the A/C idle pulley geometry haven’t changed.
Hence, Honda made the changes at the CL/Pulley design on P9K compressor.
https://lh4.googleusercontent.com/-J...40/img_001.jpg https://lh4.googleusercontent.com/-e...40/img_002.jpg
CL/Pulley on P9K spec at the left and the ones on the PR7 spec at the right.
As you can see, the edge of the A/C belt is much closer to the face of the compressor body on the P9K.
So, this is the reason why you need to keep the correct combination between the CL/Pulley and the Bracket because the compressor body dimension is the same.
In fact, if you order the OEM one, it doesn't come with the CL/pulley so you will be forced to re-use the existing parts any way unless you pay the extra for the additional parts.
I have never ordered one but I believe the remanufactured Denso one will come with the CL/pulley.
Kaz
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Kaz, as always very helpful information. I have read a number of previous posts relating to the compressor and R12 to R134a conversion. These indicated that if continuing to use the PR7 compressor this would likely soon fail after conversion to the new gas.
On the basis the PR7 compressor was used / supplied by Honda until 1997 as a R134a system why is it not acceptable (good practice) to continue to use the original compressor? Many thanks
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Hi, Button.
Not sure I understood the point of your question especially the term ‘original compressor’ so I will answer based on two different points.
If your question is related to the usage of PR7 compressor on R12 as well as on R134a system, then please note that there are two major differences among the PR7 compressors.
One for the R12 and the other one for the R134a system. There are also minor differences within the R134a PR7 compressors but I’ll leave them for now.
Based on so many conversion (R12 to R134a) done in Japan (you don’t want to drive a car without A/C in Japan, so hot and humid, one of the reason why even Type-R/NSX-R owners install the A/C), it is safe to say that if R12 PR7 compressor was kept using with R134a gas after the conversion, sooner or later, it will fail requiring another A/C service.
Addition to the new compressor, you will need to replace at least the receiver/drier again that was already replaced at the time of conversion so waste of money for the parts/labour.
Also, many owners tend to leave the sign of compressor failure until it gets really noisy that by the time the system was opened, lots of metal flakes were stuck inside the condenser causing another expensive repair.
Please remember, the receiver/drier is located after the condensers.
So, knowing that the R12 PR7 compressor will fail in the future after the conversion and for the prevention of serious expensive repair, instead of duplicating the same tasks, it is always recommended to replace the compressor to the latest R134a spec one (P9K spec for our NSX) at the time of conversion. Needless to say, you are going to disturb the system connection so you must replace the receiver/drier (and the expansion valve).
If your point of question is why it is better to use P9K compressor (only R134a spec available) instead of R134a PR7 one, then please keep reading below. Otherwise, please ignore it.
Nothing wrong by keep using the R134a PR7 compressor until it fails but you will notice much higher friction (eng power loss) when PR7 comp was engaged than the P9K one.
When you drove R12 PR7 compressor equipped NSX (mainly 91 model some 92 one), you won’t notice too much power loss when the A/C was engaged.
However, after the introduction of R134a PR7 comp, you would notice some eng power loss under the same condition.
P9K comp has improved friction loss and thus, it won’t eat up eng power like the R134a PR7 comp.
If your R134a PR7 comp started sounding bit louder than it used to be, best to act early before it turns into grinding noise. You don’t want to let metal flakes inside the A/C pipe system and most importantly, block the condensor…
Quite often, when you replace the compressor to a new one, you will be amazed how quiet it can be when the A/C has engaged.
Hope I answered at least part of your question…..
Kaz
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When I changed my old A/C compressor of my 91 I went with new parts from a 94.
- new compressor
- new stator
- new clutch
- new receiver R134a with new bracket (Kaz metioned above) (R134a is not compatible with R12 receiver chemicals)
- new o-rings (except at the expansion valve, kaz explained why), there is a R12 and a R134a version, watch out for this difference.
- new valves IN/OUT, you don't need to buy the hole pipe because of a £0.1 part
- biggest problem of all: how much oil (R134a) has to be added? It's 120-140 m. But how much did you add in the past and how much remains in the system? Wild guess. The most expensive way: flushng each component.
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Dear Kaz, thank you for the explanation and pictures. That's very good to know.
So in order to move the a/c compressor a few mm to the right, to gain a bit more clearance between the tubular exhaust header and the compressor, you can use the 1997+ compressor bracket (currently part number 38930-PR7-A01). Then, in order to keep all of the pulleys aligned, you also need to use the thinner 1997+ a/c compressor clutch set (currently part number 38900-PR7-A04).
Two years ago, when I installed a new a/c compressor, I ordered an R134a 38810-P9K-E01. Thankfully, I reused my compressor mounting bracket and compressor clutch set. More by dumb luck than anything else, it seems my three a/c pulleys should therefore still be aligned. Nonetheless, with the help of your pictures, I'm going to try to make sure I have a thick, earlier-specification clutch set since I believe I should still have an earlier-specification mounting bracket on my 1991.
goldnsx - when you changed your a/c compressor, it's good that the earlier clutch set was still available. According to the US parts catalog, clutch sets for the 1991-96 model years are no longer available even though the earlier mounting bracket is. If anyone buys a new clutch set today, hopefully they will make sure they use it in conjunction with the correct compressor mounting bracket.
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Greenberet i am inclined to agree with your logic reading all the posts but will defer to Kaz / others for confirmation.
Kaz thanks for your detailed answer to my query above, your 1st part fully answered my question as i have a R12 version of the PR7 compressor - i understand now with there being differing versions of the PR7.
Sorry a couple more queries
1/ reading posts am i correct in assuming you can re use the CL and pulley from the R12 PR7 and put them on the P9k?
2/ I now understand need to replace my R12 PR7 Comp on gas conversion. Has anyone now ordered and received the compressor set from Rock auto to clarify what clutch / pulley configuration it comes with? This will influence whether to consider reuse of CL and pulley ( subject to being able to or need to also get the later bracket)
Many thanks
John
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Hi, Button.
1. Strictly speaking, the CL capacity is different between the two but when doing retro fitting using the OEM compressor, I never saw any issues for many years by re-using the R12 CL/pulley on the OEM P9K R134a compressor.
2. I think some owners bought the compressor from Rock Auto so hope they will provide some feedback.
If I remember correctly, there were 2 model no. for re-man R134a Denso compressor and I think Rock Auto (and possibly even Denso) was not listing it properly against the year model as they don’t know when the bracket was changed. If your CL/pulley assy is fine, just re-use OEM one if there is enough clearance against the compressor face.
Kaz
