alan911sc

Can anyone give the operating parameters of the high pressure/low pressure AC cut off switch,static pressure at the compressor on the high and low pressure side, and the same pressures while the compressor is operating. Car is a 1990 C4 with R-12.I have access to AC equipment at a friends repair shop and need some info before I trouble shoot and begin to tear apart.

Randall G.

Hi Alan,

-17.5 bar = "Mean Effective Pressure Switch" tells the condenser fan to run in fast-speed.
-2.5/27 bars = high/low pressure switch set-points.

The mean effective and hi/low pressure switches are both internal to the "3-way Freon Pressure Switch."

You can find two of the operating parameter curves for a R-134a charged system here:

<a href="http://forums.rennlist.com/cgi-bin/rennforums/ultimatebb.cgi?ubb=get_topic&f=4&t=002230&p=" target="_blank">AC Link</a>

There's a third curve (high-pressure vs. ambient temp.). Also, keep in mind that the R-134a and R-12 operating curves are different! If you would like the R-12 curves, let me know. I'll scan 'em and send them on.

Sorry, I don't know the system's static pressure.

Don't know what you have in mind, or if you have a source for $R-12$, but you might want to give serious consideration to converting to R-134a.

Good luck!

alan911sc

Thanks again Randall,

I just received a Bentley and the curves are shown in the maunual. I do have some R-12 stashed and intend on going with it. I did find that the compressor clutch pulley does not line up with the engine pulley and it does not appear to be enough room to move the compressor back to make it line up as the intake runner is right up tight to the compressor. Would you know the correct compressor model and number and the correct model and number for the clutch. It appears the clutch may have been replaced as a new wire and connector
has been crimped on. The clutch is offset about a half inch so I do not know if the shaft is too long (compressor replaced) or wrong clutch installed. Thanks again to all of you at Rennlist as I must have paid for my membership a hundred times with all the valuable information I've received in my first two months of membership.

Randall G.

Hi Alan,

Almost forgot. Does the Bently manual give the R-12 and oil quantities? Suppose you'll need those when working on your system this weekend.

I'm sure I can give you the Porsche part number for the compressor, when I get home and have a chance to look at PET. I don't remember if the Porsche part # is on the compressor anywhere. I'm almost positive that PET shows the compressor as one piece, and won't show a separate part # for the clutch. If it will help any, I can take dig. pics of my own compressor/clutch, and send them to you.

Model numbers ... I'm sure this won't be listed in PET, but it's probably on my own compressor. But ... my compressor is from a '97, so it won't (shouldn't) be the same model as your own. I say that because the compressor part # changed in '93.

Talk to you soon.

Randall G.

Hi Alan,

Compressor part # = 964-126-121-01.
Repair kit magnetic clutch = 964-126-901-00.

alan911sc

Randall,

FYI and others the capacity for refrigerant as listed in the Bentley is as follows:
R12 930g 2.05 lbs.
R134a 840g 1.85 lbs.
From what I see the compressor looks like all I've seen in manuals and publications and mounts perfectly. The clutch is misaligned. Pics might be helpful. I'm wondering if there may have been a R134a conversion done and a compressor from a newer model used. Would you know if there are different part no. for a R12 unit and a R134a unit. Will get back at it shortly in a week or two because there is no need for AC in Buffalo, NY this time of year and this is one of my winter project items. So there is no rush for any additional info you can provide. Thanks again

alan911sc

Randall,

More food for thought, did some web surfing and found on ALLDATA ac compressor part nos. Very interesting:
968 model year 1992
911 Carrera 2/4 model year 1989 to 1992
911 Turbo model year 1986 to 1989
all use ac compressor pn 930 126 021 01

911 Carrera model year 1984 to 1989
" uses ac compressor pn 964 126 121 01"

911 Turbo 1991 to 1992
ac compressor pn 928 126 010 06

These numbers were indicated on ALLDATA's TSB regarding R134a retrofit. Can you verify these numbers as a 964 prefix does not appear to go with a 911 of the 84-89 vintage, as does the 930 prefix for the 89-92 vintage.

Randall G.

Hmmmm .... looks to me like AllData has their data jumbled by year, model or both:

The '91-92 Turbo definitely uses a 930 (not a 928) prefix compressor.

I'll verify this, but I'm 95% certain (or else I wouldn't have written the same above) that the '89-92 C2/C4 uses 964-126-121-01. As I recall, the number changed to 964-126-121-02 in '93.

I'll also check the part # for the 84-89 compressor.

Porsche changed the compressor part # in '93, with the introduction of R-134a. That said, it's okay to run R-134a in a pre-93 964 compressor.

Talk to you soon ...

Randall G.

Boy, AllData is way off in this case. Looking at PET right now:

-928 126 010 06 is for a 928
-930 126 021 01 is for a 84-89 911.
-930 126 021 03 is for a C2 Turbo through '92
-930 126 021 04 is for a C2 Turbo 93+
-964 126 121 01 is for a '89-92 964
-964 126 021 02 is for a '93 + 964

Hope this helps, and will talk to you soon!