dprantl

Why are you using pressures and the sight glass to charge? You should evacuate the system, then add back exactly the amount of refrigerant that Porsche specifies for the system by weight. For a '93 GTS that is 1150g of R12. With no moisture or air in the system, that is the right amount.

Dan
'91 928GT S/C 475hp/460lb.ft

SQLGuy

With, or without, rear A/C?

dprantl

Here are the official figures for R12:

- Up to June 1988: 1050g without rear A/C and 1200g with rear A/C
- As of July 1988: 950g without rear A/C and 1150g with rear A/C

The dates may not be completely accurate (they may be actual auto manufacture dates), since I believe the difference in refrigerant amount is due to the switch from the 6E171 compressor to the 10PA20C. This happened for the GT/CS in '89 model year and for the S4 in '90 model year.

And just for the sake of completeness, system oil amount:

- 6E171: 280 +/- 20 cc Denso 6
- 10PA20C: 120 +/- 20 cc Denso 6

Pay attention to the huge difference in oil amount between the two compressors!

Approximate distribution of oil in the system:

- Compressor 40%
- Evaporator 35%
- Condenser 15%
- Receiver/Drier and lines 10%

Dan
'91 928GT S/C 475hp/460lb.ft

SQLGuy

Hmmm... quite a bit of oil for the older compressors - almost 10oz.

Anyone know whether POE is 1:1 by volume for mineral oil when looking at these types of numbers?

dprantl

You should be adding the same amount of oil, regardless whether it is PAG, ester or mineral.

Dan
'91 928GT S/C 475hp/460lb.ft

ROG100

Cobalt,
My 93 is R134a and blows at about 30F in traffic with a 100F+ ambient.
However on my earlier cars I still use R12.

Currently my 93 is not blowing cold due to a fried AC compressor clutch.
I have been following Craigs progress as our issues with vacuum in the HVAC system are similar.

Tails - awesome info and should be added to the write up produced by Wally.
I need to understand better how the stepper motor controls the air.
I will pull a late HVAC box apart and take some pictures.

Pcplod

I have been following the thread and was wondering if I am correct in assuming that the pre-June 88 amount is correct for my '86.5??

Thanks for the info!

dprantl

Yup, your '86.5 definitely came with the 6E171 compressor.

Dan
'91 928GT S/C 475hp/460lb.ft

cobalt

30 degrees, Seriously? I have never seen a car blow that cold nor a house. The system doesn't freeze up blowing that temp? If I see a 40 degree drop in temp i consider that to be a great working system. I have never seen a system drop the temp 70 degrees before out of any a/c system.

If you say it is so I will believe you but it is contrary to what i understand an a/c system can do.

Edit:

Is anyone else seeing temps in the 30's? I just went and checked on my 08 Chevy Avalanche and my fathers E500 MB. Both newer cars with great A/C with an ambient outside temp of 89 degrees the chevy was blowing 46.8 degrees the MB was blowing 45.9 at 1500 rpms. Both these cars cool down quickly. So we are looking at roughly 42 degree drop at a cooler temp. I would assume if we were at 100+ degrees it would be closer to a 40 degree drop.

For the record I used all recently calibrated measuring devices. I know with 52 degrees coming out at 100 degree external temps my GTS is quite comfortable.

Tom in Austin

I am following too, because Sean is going to fix my A/C this weekend! Blows about 65 deg in 100 ambient, which means when first getting into the car on a hot day, it takes about 2.75 hours to get comfortable.

I think the heat has fried my brain ... lol

ROG100

My house blows about 60F at the vents with an IR.
My Chevy Van blows 35F but the evaoprator does freeze on long runs. Melts pretty quickly though.
My 87 hits 29F at the evaporator in the center vent with an IR.
My Mercedes is about 33F at the center vent.

IIRC the WSM for 94 R134a is 29F at our high ambients here in Texas. I just checked the WSM and you should get 3C (37F) at the center vent when the ambient is 40C (104F). The IR picks up the temperature on the evaporator so that is why I read 29F.
I am by no means an expert but the freeze switch stops the evaporator freezing on our cars.

I could not drive in a car blowing 60F here in TX.

dprantl

An IR gun pointing at the evaporator may not be the most accurate way of measuring vent temperatures. I use a digital thermometer stuck into the center vent which measures the air coming out of the evaporator.

That said, my converted R134a system will cool down my heat-soaked black car in 100deg F Atlanta humid summer very fast (faster than my wife's '02 C32 AMG). I should measure the temps and post them. A properly converted R134a system with enough condenser capacity should work just as well as R12 unless you live in the middle of a desert.

Dan
'91 928GT S/C 475hp/460lb.ft

CraigL

Hi Dan,

While I am not an HVAC tech, I suspect that the ports and the sight glass really are there for a reason. Maybe the best way is to weigh the charge but initially I didn't have access to a scale. Bottom line: if I can't tweak the system to my satisfaction using the gauges, I will re-evacuate (recover) the R12 and introduce the right amount by weight. Right now I think I'm in the zipcode.

Thanks for posting the oil capacities. I put a total of 140cc in my system and distributed it according to the WSM just as you posted.

Best regards

Bill Ball

As Dan says, I have found IR guns to be very misleading for vent temps, grossly under-reading the temp. They don't do well measuring against black objects. I've seen -20F readings in the vents. With a standard thermometer, my 89's AC will blow 30F out the vent at 90F ambient IF the car is not heat-soaked. My freeze switch may not be doing its job, although I've never had noticeable icing issues, probably due to reasonably low humidity, so I've never bothered to work on the freeze switch. It is stated to be spec'd to cycle between 32 and 40F.

I look for 50-60F differential vent versus ambient. Tom's 65F at the vent in 100F ambient is not adequate (35F differential), again, if the car is not heat-soaked.

Like Dan said, the charge should be based on weight into an evacuated system, which is what Craig did initially. Short of that, the sight glass does work well as an indicator for R12. Check with the system running at 1500 RPM and any charge being delivered shut off for the moment. You can also feel the tubes into and out of the receiver drier - they should be the same temp. If the line from the condenser is colder, that's another sign of undercharge. If the system is overheated from running for a long time while stationary, pressures and these indicators can be misleading.

cobalt

I will agree I would not trust IR thermometer. I am using a Fluke 52-2 and J thermocouple industrial grade calibrated quarterly, adjusted for correction factors. I have found even the Fluke IR units to be misleading, although I normally use this equipment to measure between 425 and 2300 degrees F.

I must admit I am perplexed by these numbers. New or old of every car I checked I have rarely seen more than a 45 degree differential. My cayenne feels like an Icebox and it is one of the better differentials i have seen and it averages about 44 degrees.

Either I am not getting my thermocouple in deep enough or just call me a skeptic. Can someone explain how they achieve such a large differential? I recently evacuated my entire system and recharged it everything to spec and I am only seeing a 43 degree differential. My turbo also runs about the same as has every other Porsche I have owned. My C2 was the same that is until I ripped the system out to save 50 pounds.