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Porsche 930 A/C Help Needed

rs4lb on Fri July 10, 2009 7:49 PM User is offline

Year: 1986
Make: Porsche
Model: 930
Engine Size: 3.3
Refrigerant Type: R134
Ambient Temp: 75
Pressure Low: 45
Pressure High: 250
Country of Origin: United States

I'm trying to get my A/C sorted out on a 1986 Porsche 930 and am running into some problems.

This system was converted from R12 to R134 a few years back.

It stopped working (blew warm air) in January and required a new expansion valve and a new receiver drier because they were "plugged up".

System capacity is listed is 48oz of R12.

I'm currently having the following problem:

If the A/C shop pumps down the system and fills it with the proper R134 charge (40oz per the shop), I am getting warm vent temps.

I've listed the corresponding vent temps/pressures below with various differen't charges, all at about 70 degree average ambient temp.

1. 40oz R134 charge- Idle Low Pressure 55lb, High Pressure 260- 61 degree freeway (3000RPM) temp, 65-67 degree idle vent temp.
2. 30oz R134 charge- Idle Low pressure 45lb, High Pressure 240- 61 degree freeway (3000RPM) temp, 65-67 degree idle vent temp.
2. 16oz R134 charge- Idle Low Pressure 25lb, High Pressure 225- 48 degree freeway (3000RPM) temp, 61 degree idle vent temp

I know I've been able to get vent temps in the mid 40's and I'm trying to understand why the system is showing high low side pressures and normal to slightly elevated high side pressures.

Thanks for any insight.

Mike

rs4lb on Fri July 10, 2009 7:53 PM User is offline

Just to add a bit.. if I raise the idle to 1800-2000RPM all of the low pressure values listed above drop around 5-7PSI.

Is it possible the expansion valve installed is for R12 and not R134? Would this cause this kind of problem?

Edited: Fri July 10, 2009 at 8:13 PM by rs4lb

bohica2xo on Fri July 10, 2009 11:49 PM User is offline

1) 911's have never been known for "meat locker" A/C.

2) If you convert one to 134a, the marginal condensor becomes even less effective.

3) If your TXV "plugged up" after a 134a conversion, the conversion was not done properly - most likely a "death kit".


250 psi high side readings @ 75f ambient point to a horrible condensor ratio. Most likely the condensor is also clogged with the desicant from the failed dryer - the same stuff that "plugged up" the TXV. When the dryer is not replaced with one rated for 134a during conversion, this is the result.

The differences from 16 ounces to 40 ounces make me wonder about the compressor as well, but at that low ambient it is hard to say for sure. Your first step is a total system flush. A careful inspection of the TXV as it is removed for additional debris should be done. Flushing everything (except the compressor) completely clean & dry is the only way to get the proper oil charge back in. Too much oil will really hurt cooling, and death kit conversions usually leave the old oil in place - then add a second oil charge.

The compressor can be flushed with clean oil of the same type as you plan to use in the system. See the FAQ's for details. I would recomend BVA 100 ester oil for this unit.

What type of condensor is currently installed on your 911?

B.

-------------------------
"Among the many misdeeds of the British rule in India, history will look upon the act of depriving a whole nation of arms, as the blackest."
~ Mahatma Gandhi, Gandhi, An Autobiography, M. K. Gandhi, page 446.

rs4lb on Sat July 11, 2009 2:09 AM User is offline

Thanks for the note.. The receiver/drier was replaced along with the TXV back in January.. Not sure if the shop did any kind of flush etc..

The compressor is a nippondeno unit.



Edited: Sat July 11, 2009 at 2:12 AM by rs4lb

rs4lb on Sat July 11, 2009 2:50 PM User is offline

Condensor is original tube and fin

bohica2xo on Sun July 12, 2009 3:46 PM User is offline

The original T&F condensor can be flushed. Flush the metal system parts back to bare metal (except the compressor).

Hoses can be flushed, but if they have an inline filter or muffler (can) you should consider replacement if you had a desicant bag failure.

You posted "freeway" numbers. Was this actually freway operation, or 3,000 rpm with the engine cover open? Astronomical high side pressures are common with the condensor at zero airflow.


The condition of the TXV inlet should tell you something about how clean the system is. The evaporator can be harder to flush well, and if you see debris past the TXV you will need to clean that up.

There is no "proper" charge level for a conversion. I would return to 48 ounces of R12 if I owned that 911.

B.

-------------------------
"Among the many misdeeds of the British rule in India, history will look upon the act of depriving a whole nation of arms, as the blackest."
~ Mahatma Gandhi, Gandhi, An Autobiography, M. K. Gandhi, page 446.

rs4lb on Sun July 12, 2009 8:25 PM User is offline

Freeway #'s are actual freeway operation.

Pulled the rear condensor and flushed, it was clean.
Pulled the evaporator and flushed, it was clean as well.
The TXV is totally clean as well.


I did discovered (based on their invoice) that the shop who repaced the TXV back in January listed a BMW 528 part # on their invoice (64 51 1 468 475), which I thought was strange.
In any event, the TXV is made by Egelhof and there is a stamped number on the side RW31 3300.

Is there an easy way to test TXV function?

Thanks.


If this is the wrong TXV or if the TXV was designed for R12, would this cause high low side pressures?

bohica2xo on Mon July 13, 2009 12:21 PM User is offline

Testing the TXV requires access to the valve. You can check pressures while heating & cooling the sensing bulb.

Failure to properly mount & insulate the sensing bulb for the TXV will cause performance issues. If the shop that installed the valve failed to get a clean, secure coupling of the bulb to the evaporator discharge line - in the right position, you will see degraded performance.

B.

-------------------------
"Among the many misdeeds of the British rule in India, history will look upon the act of depriving a whole nation of arms, as the blackest."
~ Mahatma Gandhi, Gandhi, An Autobiography, M. K. Gandhi, page 446.

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