Time for AC

soxnail · 08-21-2015, 01:06 PM

Now that the broken exhaust stud issue is done its time for the next item on the list.
Needless to say since the car has sat for 3 years or so its AC does not work. After a lot of reading and research here is what I have.
The system had been converted to R134a in 2005 by a Porsche dealership. ( Porsche of San Antonio). It worked for a while and then got weaker and weaker. Since I was only using the car intermittently and not needing the AC I did not fix it.
So now that I need it here is the status:
The system has 35 PSI in the low side.
The system has 35 PSI in the high side (same reading on both).
The AC relay G17 works as it is supposed to.
The low pressure switch is on.
When I turn on the AC the fan cuts on, and the compressor clutch pulls in.
The compressor turns freely by hand.
With the compressor turning (AC) on the low and high pressure stays the same.
looks like a compressor failure right?
But...when I first started working on the system the low side was getting sucked down to around zero with the AC on.
I evacuated the system 30 inches for 20 minutes, left it alone over night and the vacuum was still 28 inches in the morning.
Redid the evacuation and charged it to 35 psi. It only took half a can of r134a seems very little, but did not want to over charge it.
Now when I turn on the AC the compressor turns but the low and the high side don't budge.
the low switch is on(checked with meter and the clutch is in).
Any clues to what is going on.
TIA
Sox

soxnail · 08-21-2015, 01:52 PM

update
Ok need to learn how to use the gauges...
with ac on its 37 psi lo and 210 hi (temp here is 92 deg.
When I turn the AC off the lo side climbs 190 psi plus. Is this right ?
BTW it took the rest of the 16oz can to get to this point.
The air is still coming out warm.
Sox

mytrplseven · mytrplseven's Garage

Are you sure it's the a/c and not the little nylon clip in the a/c mix box under the dash? If the heater shut off valve is stuck open, it will overwhelm the a/c and make you think it's not working, also. See the Clarks garage articles on this.

soxnail · 08-21-2015, 06:07 PM

Thanks mytrplseven
You may be correct...but the low pressure line is barely cool in the engine bay. The high line is hot.
I would think the low line would be cold ?
S.K
Ps. looking at the mix box now.

soxnail · 08-21-2015, 06:20 PM

Just one more, it does blow hot when I set it to heat...and barely coolish at full cool.
Sox

soxnail · 08-26-2015, 06:29 PM

Does any one know what these Vents? are for ? There are 2 of them one on either side of the evaporator. They were covered with old foam insulation, so I don't think any thing was getting through them. I saw a pic in a post by Bazar01 in the Porsche 924/944/968 Technical Forum which also had them covered with foam.
Here are mine with the old dead foam cleaned off. Just showing one side.
Thanks Sox.

My Pic

Bazar01's pic

soxnail · 12:02 PM

Bump....in case someone has the answer to the above question.
Sox

soxnail · 09-12-2015, 02:21 PM

Ok just put some auto/marine sealing strips on as gasgets. Hope this is right. see pic below.

BTW found the issue it was the mix flap auto control....
Still the air is cool but not cold, in my research I find that the pressures and vacuum commonly listed for the 944/951 ( 35 low 210 high) for the temperature where I am at is for R12.
Apparently R134a is to be run at a lower pressure....another source says needs to run at a higher pressure. ????
I am at the above posted numbers, but as I said its only cool not cold. Recon my pressure readings are not right for R134a ?
Thanks guys
Sox

soxnail · 09-12-2015, 02:45 PM

I am going with the posts in this thread
A note about A/C sytem pressures in the 924/944/968 section
Sox

911tracker85 · 09-13-2015, 07:30 AM

i get my cars charged at the shop where I rent the garage.

just finished reinstalling the AC in my 951 DE/street car. YES, AC in a track car. I prefer to look and feel good than shave a second off my lap time.

full evac, then push in the appropriate amount of refrigerant. I found when doing my first AC system on the 928, trying to get it right by gauge pressures was a bit of a challenge and subject to error.

good luck.

soxnail · 09-13-2015, 01:27 PM

Thanks Bob,
Will go down this route too. I have to go and have the R134a taken out (reclaimed), first then will do the refill.
I read that 30 Oz is the correct fill for this car, You concur?
Sox

McLovin · 09-13-2015, 10:00 PM

Not sure if I'm missing something, but I think you said you fully evacuated the system, then refilled with one 14 oz can.

That's not enough R134. I don't know the exact capacity for your car, but it will be much more than 14 ozs.

Most cars seem to be around 30-35.

McLovin · 09-13-2015, 10:01 PM

Be sure to purge your freon supply line before filling, too.

soxnail · 09-14-2015, 07:21 AM

McLovin (great handle)
It was a 16Oz can, and yes my mistake should post complete stuff I put in almost 2 full cans. so 16Oz plus most of another 16Oz. So about 30 + Oz.
I did purge the fill line by allowing some gas to come out at the coupling by loosening it, about 3 seconds worth.
Thanks Sox.

soxnail · 09:36 AM

Update:
1)Had all the old refrigerant taken out.
2) Evacuated the system to 28 inches for 30 minutes.
3) Charged system with 2 cans of 16 Oz R134a (minus the purge gas to clear the lines).
4) Car air is coolish only.

Numbers ambient :
Temp = 88 Deg F
Humidity = 70%

At 2000 RPM the gauges read:
Low = 34 PSI
High = 345 PSI ....Is this too high ? Could I have too much compressor oil in the system ? Too much charge ?

Thanks Sox

McLovin · 09-14-2015, 11:01 AM

Did you monitor the pressures while you were filling? Because 345 seems way high.

I did a couple of my old cars in the last few weeks, one of them hasn't had working AC in at least 2 years, the other was a little low.

On the first one, I drew a vacuum for a half hour, let it hold for a half hour, then refilled using the gauges. I kept filling until the high and low pressures reached the right specs.

The second one was just a top up, but same thing. Refilled, while watching the gauges, and stopped when it reached specs.

Both are ice cold now.

soxnail · 09-14-2015, 04:13 PM

I did the first time and stopped at 37 lo and 210 high...which only took 16 Oz. Air was warm.
After more reading and advice like from 911tracker85 above I got it vacuumed and went with the "get the right amount of charge in " school of thought.
The pressure readings I have posted above reflect the results from approximately 30 Oz (840 grams) of charge in. The car is coolish but not cold.
Thanks Sox