930_pit

Good day!

It's getting hotter now adays especially here in Las Vegas. I need a recharge on my AC. I spoke to one porsche mechanic before that when charging the AC, there is a certain pressure that is best for the 930 to attain the maximum coldness of the system. If the pressure is higher than that desired number, the AC does not become as cold as it should be. I just forget the amount of pressure which he told me before.

If somebody knows the correct amount of pressure, kindly let me know. I am planning to bring the car tomorrow to a shop for a recharge.

By the way, the car is 1987 930 and has a stock AC system except for the new barrier hose with R134a refrigerant.

Thanks!

Benny771

Little off topic:

Have you ever thought of that 134/12 substitute. You can buy it a Walmart and it has better cooling properties.
I havent changed it in the p-car yet but the Corvette and Saturn have it. You can install it your self (kit).

Red-tek http://www.redtek.com/home.html

And duracool http://www.duracool.com/

911rudy

Benny I believe you are mistaken on the cooling ability of 134a to R12. It does not cool as well and must operate at a higher pressure which is bad on our old systems. If some of the OEM components are replaced with more modern pieces it can be as good as the R12 systems. I have an all new system and it cools good but not great compared to a new cars system. Part of it is the poor design and layout of the original system. But hey, its over 20 years old.

A930Rocket

Believe it or not, the original hoses had small holes in them to bleed out the freon over time. When 12 was cheap and easily had, it was no big deal. R134 has a small molecule and they can escape the old hoses even faster. If your going to use R134, you need the barrier hoses like Rudy.

I've used the Duracool with good results on my R12 system.

If you look inside your engine lid, you'll see how much is need to charge the sysem. Also, if you look at the receiver/dryer, when the there are no more bubbles, the system is full (a rough guide).

JFairman

There is no one high side pressure you aim for with R134. It all depends on ambient temperature.
This chart takes a little math with a calculator and really pinpoints the high side pressure you want better than any other chart or formula I have tried.

If you use R134 the label in the car will not be correct. You use a different amount of R134 than R12 in an AC system and the sight glass on the reciever dryer, if you have one does not work accurately with R134.

This chart is for high side pressure at idle speed.

As an example... if it's 85 degrees outside than multiply 85 x 2.4
That comes to 204.
Now multiply 204 x 1.05
That will give you the high side pressure you want to shoot for with the engine lid down so air is being sucked in over the rear condensor, and the front condensor fan is running.
The pressure at idle with outside ambient temperature of 85 degrees should be right around 214.2 psi
It will go higher as engine rpms raise, and when ambient temps are higher.

80-85F = ambient times 2.4 X 1.05 or the + 5% rule
86-90F = ambient times 2.4 X 1.1 or the +10% rule
91-95F = ambient times 2.4 X 1.13 or the +13% rule
96-100F = ambient times 2.4 X 1.15 or the +15% rule
101-105 = ambient times 2.4 X 1.17 or the +17% rule
106-110 = ambient times 2.4 X 1.20 or the + 20% rule

Benny771

The product i said to try is not r12. It is a r12 substitute.
According to othe manufacturer it had the largest molicules compared to R12 and 134a (less likely to leak out). And its cheap.
I have been putting it in friends and neighbours cars for approx 8 years not.
But if the system has a hole, nothing will stop it from leaking.
I do evac the system to approx -30psi for an hour then leave it overnight and check if the guage has moved. If good, fill away!



P.S I wish i could find spell check on this site........

930_pit

Thanks for all the info!