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!

abe

The pressure is dependent on the ambient temperature....
This is realy a DIY and they have a few different kits at the auto stores. According to my kit chart for
R134 a
ambient t low side charge high side charge
65F ******25-35psi********135-15psi
75 ****** 35-45**********150-170
85 ****** 45-55**********225-250
95 ****** 50-55**********275-300
105 ******50-55**********340-345

This should give you an idea. I do have a complete R134a A/C
abe

TA911-64

930_pit, What's important is the amount of R134 on re-charge. Abe is right-ambient temp changes pressure, but realise that too much or too little freon compromises coldness. I think your Porsche mechanic was referring to the "right amount" of R134. If you go to a reputable A/C shop they should
have your car's specs on file. (Also look in your manual-it's there). If they do it right they'll evacuate your whole system and charge accordingly.

scottb

These pressures were posted on Pelican by the resident a/c guru there:

Typical high side pressures (without adjustment for altitude):

For R-134a
70 to 80 F ambient 115 to 200 psi
80 to 90 F ambient 140 to 235 psi
90 to 100 F ambient 165 to 270 psi
100 to 110 F ambient 210 to 310 psi

Typical low side pressures (not adjusted for altitude):

For 134a
33-50 F Evaporator temp 16 to 29 psi
33-60 F Evaporator temp 19 to 39 psi
40-65 F Evaporator temp 25 to 43 psi
48-65 F Evaporator temp 37 to 51 psi

Of course, any time you recharge an a/c system in a 911, it is important that the idle be kept at 2000 rpm, and that you have a good amount of air blowing across the rear condenser. The deck lid should in down.

If you're going to do the work yourself, be VERY careful. Be sure to wear gloves and eye protection, at a minimum.

Good luck!!

Amber Gramps

When I recharged one of my cars I was told the "synthetic" R-134 was going to give me 10degrees lower temp. Now it's freakin' cold.

930_pit

Thank you guys for all the info!

whalebird

I think its important to note that 134 is different than R12. R134 requires less freon to achieve the same pressure differential required to work. An undercharged system cools better at idle than an overcharged system. Any tech should be able to put gauges on the thing and see what its doing.
Remember that the high side pressure(numerically) is the temperature (numerically) of the condenser. And, the low side pressure is the temperature of the evaporator.
R134 is more "spongy" than R12 and less is required to get the balance right.

whalebird

one more thing. The sight glass on the drier is useless with R134. You have to read the gauges.

tone40

as well as the temperature.

For example,

70 degrees at 20% relative humidity has a low side of 37 psi and a high side of 225 psi. 70 degrees at 60% is 37 psi and 290 psi.

100 degrees at 20% is 38 psi and 325 psi. 100 degrees at 60% is 60 psi and 445 psi.

All readings are based on 2000 rpm with R134A.

whalebird

Good point. Humidity is a big factor. Just looking at the numbers is frightful. Could you imagine what could happen if the DIYer is juicing up his a/c and 445 psi let go. It could be disasterous if your pressure switches don't work.

930_pit

Thanks again for the additional info and advises!

originalmotorhead

Is there possibly a good write up on DIY recharge for the 80's era 911?
I've got a 1980 911sc and there's nothing in the sight glass and compressor does kick on but no cold air.

Tom

originalmotorhead

Found a good link.

http://forums.pelicanparts.com/showt...ghlight=hladun

Tom

RacerX1166

I'm getting to where I'm about ready to do a recharge myself. The system was converted to R134 late last year but, since barrier hoses weren't installed, the system has leaked itself into pushing ambient temp air at this point.

I plan on investigating a full upgrade next year but, if I wanted to recharge the system myself this year, can anyone point me in the direction of a decent setup to get the job done?

928Collector

Anyone know what temperature a working non leaking r134a conversion should blow ac air at?