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Now that's some good info. Thanx again!

Quote:

Originally Posted by kuehl (Post 8716610)

With R12 this is typically a sign of an undercharge, but don't add more refrigerant yet.

The liquid refrigerant is changing phase, from a liquid to a gas, before it exits the expansion valve (also called a TXV or TEV). In a normally running system the only condensation or frosting you will see is on the evaporator outlet pipe where it exits the evaporator. What you are observing is related to either:
A) Moisture in the system that is freezing and creating a small aperture large enough to allow the the liquid refrigerant to change phase (liquid to gas), or
B) A partially closed TEV, most likely do to moisture freezing inside it. I would not replace the TEV just yet.

The moisture problem usually happens when the system is not properly evacuated (pulling a vacuum on the system) to remove ambient gases (air) before you put the refrigerant in the system.

Just a suggestion before you spin your wheels tearing things apart.
1) Properly, what you would want to do is as suggested, replace all the o-rings in the system if that has not been done before, the original o-rings would be hard and brittle by this time. Replace the receiver drier because over time the desiccant inside gets saturated with moisture. Fix the leaks before put more refrigerant in the system, the most common leak points are the compressor to condenser hose, the compressor, the condenser to drier hose; tell tale signs of a leak are refrigerant oil a the leak point. Since the system has been leaking refrigerant it probably lost refrigerant oil, how much is always a guess, however if you inject or add 2 to 3 oz of refrigerant oil (you can use Ester type for this scenario) you will be ok.
2) Properly evacuate the system using an ac vacuum pump. Charge the they system with the R12 if you wish using the OEM charge amount (there should be a label in the engine bay noting how much), for a 944 its around 2 lbs or 32 oz.
3) Use a set of service gauges to inspect and monitor the low and high side pressures along with a Pressures and Temperatures chart for the type of refrigerant you are using.

Judging by all the replies and what I have researched seems like it is the receiver/drier. The system seems to be all original so I will follow your advise to replace all O rings and the receiver/drier, even the expansion valve if I find the correct one. If I have to replace the valve later do I have to evacuate the system again? If yes I will definitely replace the valve now. I will stick with R12.

Quote:

Originally Posted by Thunder-71 (Post 8720268)

If I have to replace the valve later do I have to evacuate the system again? If yes I will definitely replace the valve now. I will stick with R12.

Yes, IF you replace the expansion valve later, you will need to evacuate the system AND completely remove the unit under the dash, OPEN up the blower case and remove/replace the expansion valve.

The more you practice the easier it gets ;)

J_AZ

Quote:

Originally Posted by John_AZ (Post 8720294)

Thanks John, I hope I will not have to practice too much. What is the best source for the expansion valve. Our host here does not carry the early one for my 1984. I have a couple suggestions here for aftermarket but I would rather use original Porsche or equal, a few extra $s may eliminate extra "practice".

Quote:

Originally Posted by thomasryan (Post 8717318)

kuehl/griffiths is the man for Porsche AC stuff....under the VW number 477-820-909-00

Griffiths.com

...and if you want the best cooling if switching to R134a

Porsche 944 AC Condenser 94457301101

Where ever you get the expansion valve, double check for correct part.

I ordered locally ---number & picture matched and was sent the wrong part.

GL
J_AZ

^^^^^^^ John. Not trying to be a Richard here, but what would that condenser do? 3-4 degrees at the vent? 500 bucks is a lot of coin for a little extra comfort, and probably only on the hottest days. Or do they have a graph which shows the benefit? I haven't researched it, but when I get my 944 it will definitely be converted to R134.

Griffiths would have the technical information on the dual core/parallel flow condensers.

Most newer vehicles have the upgraded condensers. They are more efficient.

In an older vehicle, with the AC system in OEM condition, switching from the OEM to the upgraded condenser you could expect up to ~ a 1/3 cooling improvement with R 134a.

I do not have the technical information on the 944 condenser.

John

Anywhere near 1/3 improvement in efficiency would be an amazing upgrade.

Yes, I agree.
But understand, the upgraded condenser can only do its best if the entire system has been checked.

The other flaw is that if your compressor fails due to "Black Death", the tubes in the new dual/parallel condenser will clog--they are a lot smaller than 944 original condensers. Once they clog it is almost impossible to remove ALL of the filth from the compressor.

Expensive repair.

J_AZ

Ahhhhh...there's always a 'but........'

Quote:

Originally Posted by John_AZ (Post 8720493)

I have not done anything yet. Here is some more info that may pinpoint the problem. When I start the car and turn the A/C on it blows cold for about 30 seconds then just outside temperature air. If I turn off the A/C and shut the engine off and restart it 15 minutes later and turn the A/C on, again it blows cold for 30 seconds, sometimes a few minutes then warms up again. Any thoughts?

I reread Griffiths post and would begin with his advice.

My (secret-ha) source for troubleshooting is my local supplier and forum:

Automotive AC Information Forum - ACKITS.COM

GL
J_AZ

I read your first and last posts, skimmed the rest.

The system was in an unknown state, presumably empty, or near empty because it has a leak. You decided to add 28oz of R12, and the system ices up and the sight glass is foamy.

My intuition tells me you are under charged. Your system holds 40.6 ounces of R12. I suggest you recover the R12, change the schraeder valves on the high and low service ports, vacuum the system, check to see if it holds vacuum, then add the proper amount of refrigerant.

I would also check for leaks around the clutch on the compressor. Oily, dirty, grimey black crap indicates a shaft seal leak.

Good luck!SmileWavy

Quote:

Originally Posted by mattdavis11 (Post 8722649)

Hi Matt,
The A/C was working fine blowing cold, occasionally it would blow kind of warmer but in a minute or two it would blow cold again. A week ago it stopped blowing cold so I figured it needed Freon. I added two 14oz cans and one of them had red leak detector dye. I see no leaks anywhere, only place I have not checked yet is under dash. The low pressure switch by the receiver/drier is good and the compressor runs so I assume it has enough charge. Also when I start it it blows cold for a minute then warm. If I restart in 15 or 20 minutes, same thing again, blows cold for a minute then warm again.

Close the heater valve manually. It's at the back of the motor in the center. You might need a screw driver to use as a lever to close it. The other thing I would check is the valve that closes the barn doors. There are two, one passenger side, one drv. side. Check the suction from the vacuum lines. Last resort, check the vacuum reservoir, the green thing under the hood, for leaks.