How to read A/C pressures
 

I just bought an '87 911. The previous owner didn't use the A/C for two years. Needless to say, it doesn't blow cold. I'm thinking it might just be low on freon. I've got a set of manifold gauges (the car has R-12) and want to determine how much, if any, freon remains.

I imagine I can do this by hooking up the manifold gauges and reading the pressures? What pressure should the low side / high side read? Does the car have to been running with A/C on? Where are the low/high side lines on this car?

Thanks,

Scott

The LOW side is the WIDER hose the other one is the HIGH side.
The pressure on the Low side would be between 20 and 35 psi. The HIGH side no more that 250 psi.

To know if you car have the correct amount fo refrigerant to need to see if the HOT side gauge needle are bouncing, that means lack of gas. Also if the pressure of the HIGH side are closed to 250, that means that the sistem are charger.

You can see the sight glass at the drier to see if there are bubbles, if so: lack of gas. No bubbles sistem ok.

Also you can check the temp at the a/c vents to get less that 60 degrees.

Remember, if you have the opened the engine lid, the condenser have no air thru to cool it down. You have to spray some water to cool it. Also, you can put electric fans. If you car have a carrera tail or turbo tail you can do the electric fans modifications that I did. Do a search into the forum to see all the process.

Scott
If you have to ask or dont know how to connect the guages DONT.
Should you screw up and its easy, you will get liquid freon on you. In eye blind, on hands, fingers a really great burn. Leave it to someone that knows what they are doing.

Scott
If you have to ask or dont know how to connect the guages DONT.
Should you screw up and its easy, you will get liquid freon on you. In eye blind, on hands, fingers a really great burn. Leave it to someone that knows what they are doing.

Emac,

I did the A/C on my Mercedes which included a system flush, vacuum and charge. The difference is that I knew what hoses were what on that car and knew it had no freon so it was easy to know how much to put it. The Porsche is completely new to me so that's why I was asking. I hate to spend the money on a new receiver/drier and expansion valve when all the car needs is a simple charge. I just need to make sure I don't overcharge it. How much does that car hold anyhow?

Thanks,

Scott

Scott
Great news, I really didn't want to sound like a wise a@@ but Im sure you have seen and or heard of some great stories. Had a business at one time and know first hand. 300psi is nothing to play with. Anyway, my air was removed when I got her, I will look it up when I get home. But Im sure someone will post before I get the info. to you.

Scott, you'll find what you're looking for here on page 2. Scroll down to a post by scottb containing highg and low side pressure readings posted by resident A/C expert Jim Sims.

http://forums.pelicanparts.com/showthread.php?s=&threadid=344568&perpage=20&highl ight=froze%20again&pagenumber=2

No problem. And yes, A/C work can be very dangerous if you have no idea what you are doing!

Scott

This is great! This should give me what I need to get started. Hopefully it will be a simple fix.

Thanks,

Scott