Christopher Zach

So the 86.5 928S didn't have AC, couldn't hold a vacuum, and the PO did a half baked job of it with cheap 134a fittings. Given I've been down this road before with the 944S I decided to pull apart the 928 and fix the AC problems.

The leak was pretty easy to find, compressor was leaking out the front and the fittings. So a new/rebuilt compressor was ordered from 928 International, along with 8oz of PAG 46 double capped oil, a lot of O rings, and a new dryer.

Doing pretty much everything on this car is a pain, and this project was no exception. Wound up buying a small flexible magnet wand to get the bolts and washers that constantly fell into the double bottoms, pulled the compressor with a jack, pulled the condenser out and totally flushed it (full of green dye and oil, PO really didn't know much about leaks), flushed the lines, flushed the forward evaporator, etc. New condenser and dryer went in (it's best to take apart the dryer with the condenser half in the car, then assemble the condenser half way in and put on the new dryer, then the lines with new O rings, etc). new compressor went on the bottom (more rings), I did not replace all the rings but got the ones that take the highest temps/stress/pressure.

vacuumed it down, put the car on a quick 134a test (few ounces), held pressure for 24 hours. Put in 7 ounces of oil (4 for the compressor which was shipped with no oil, 2 for the condenser, one for the dryer swap), then took it down to a -30 vacuum for 2 hours, then unhooked and left alone. 24 hours later, -30. 48 hours later, -30. Fired up the compressor, hooked it in, opened the vales, no noise change which means a solid vacuum (if some air had gotten in you would hear a change in the pump sound briefly).

This afternoon I got the fan back in (hint: Put the bolts on through the bottom grille and not from the top), got the bottom bolt in (hint put it on your wand magnet to start it in the hole upside down), and tested the fan. Jumpered the hot fan switch to get the fan running at low speed, put in some R134, fired up the car, and the AC.

System took 24 oz of 134a, pressure was about 270 high, 40 low. I'll run it with this for a bit to check for leaks, but the AC is blowing rather cool and the rear AC system is working well. In addition the front fan spun up to full speed, which means the sensor switch on the dryer is kicking the fan on when the high pressure temps get high enough. I *might* put in a DPDT relay on the compressor signal line, first to run the compressor clutch off 12v directly and reduce the stress on the relay in the AC head unit, and secondly to close around the engine hot switch so the fan will run at low speed any time the AC is on (to increase condenser performance when stopped in traffic for example).

Whole project took 2 weekends and a few evenings of work. Now to fix the paint chips and such with a trip to Jeff Shaw.

Just some data points for other people working on their systems.

hlee96

Great write up and thank you!

Congrats on nice AC at the start of Summer.

-Hoi

j.kenzie@sbcglobal.net

Happy for your success. Just for future reference, it is my understanding that PAG oil does not combine well with mineral oil residue from the old R12 days, and should be used only on new systems or maybe after very thorough flushing. Ester oil is compatible with mineral oil and is preferred for old previously R12 systems, although I've heard PAG is a generally maybe higher quality oil, itself.
Good luck,
Dave

Christopher Zach

Indeed. I've used POE in the past, I know there is a serious PAG/POE/R12/etc set of opinions, from what I have been seeing the PAG double-capped oil is a lot more stable (ie: doesn't turn to acid or sludge like traditional PAG oil) and can handle some variations in a bit of residual oil/bit of water. People have said that DEC PAG is compatible with R12 and mineral residue, but I'd still say do a flush to get the obvious stuff out.

It's possible there is some mineral oil left in the system, but flushing the condenser and lines with liquid cleaner fired by compressed air, followed by replacing the compressor, and putting in the 7 oz of double capped PAG to start with should work.

One big thing to do on any conversion: The compressor to hose interfaces on each side of the compressor have a cap and schrader valve on them. This is probably some sort of vestigal thing, but the trick is those valves have R12 rubber seals and *will leak* with 134A. So take them out and replace with a pair of genuine R134a compatible valves. Then cap and forget.

So far so good. 90 degrees here, took it out for a drive, AC was cool enough to keep the interior quite comfortable. The rear evaporator doesn't blow straight to the front, but keeps the rest of the car interior pretty nice. One bug: I had a 10a fuse in the fan fuse socket and it blew (should be 25) so the front fan was not coming on. Replaced the fuse, fan came on (the temp switch on the dryer was *closed* all right :-)

Second thing that really scared me: I stopped in to get gas, filled it up, started the car, and had the flashing ! bad bad bad bad! Saw the oil pressure light was flashing, shut down. Checked oil, was at the bottom of the dipstick notch, so added two quarts to get it up to the top, fired engine up, pressure came back up and stabilized to 3 bar idle, 5 bar at 3,000 RPM. Guess the oil got hot enough to thin out and lose prime with the pump or something. But now I know the difference between

• "!" (the tail light ground is loose Chris! I'm sad)
• "!" (The tensioner alert is lit Chris, I'm Sad!)
• "!" (HOLY CRAP THE OIL PRESSURE IS AT ZERO, I AM SAD!)

I'll keep an eye on that. Meantime I'll drive it some more Sunday/Monday, verify the fan is working properly, and then see how the pressures look.

C

griffiths

Appears to be undercharged and maybe some air in the system.

Christopher Zach

Guarantee no air in the system :-) Likewise I didn't fill it to the brink, as I need to know how much R12 went into the car (it has the second evaporator, so I need to factor that in) and overfilling a system with 134 is bad. Besides if there is a leak I'd rather find out with 2 cans in. So far though working well, but I do need to replace the 25-30 fuse block, one of the next projects.

How much 134a do people typically add?

griffiths

For example, if your shark had a factory charge of 40.5 oz of R12, for R134a you'd start off with 85% of that mass or 35 oz nominal, and confirm and adjust based upon pressures and ambient temperatures.
If you feel confident you do not have any air in the system and you feel confident you filled with R134a 24 oz net (excluding line flushing), and the condenser fans were operating and your were observing that 270 psi
at idle, then your ambient was over 110F.

But if you want to sniff the system with an electronic leak detector then you have plenty of refrigerant and pressure to do that procedure.

Christopher Zach

All good points. The fan was turning at slow speed and I think I had the RPMs up to 3500 or so when I read that value. Now that I have the fans fixed properly to come on full speed I'll check it tomorrow against the temp charts to see what it looks like then fill it some more. Holy cow, leak detectors are only $20 bucks????

j.kenzie@sbcglobal.net

I bought a cheap leak detector once. It sensed refrigerant, but also sensed water vapor. I replaced an evaporator on another car for no reason because of it. Be careful.
Good luck,
Dave

griffiths

A good friend once said "you can buy oats before the horse eats them, and you can buy oats after the horse ate um".

Buy a brand name detector. Read the instructions, I'm sure there are plenty of u-tubes out there. And, get to know its quirks and how to use it.

And check your pressures at idle.

Christopher Zach

Meantime back home and starting to get ready to check things. Have my postal scale to weigh cans, and the following temp chart:

http://rechargeac.com/how-to/ac-system-pressure-chart

According to that should be 250-270 @90F. Is there a better chart?

C

griffiths

at 90 F i'd prefer to see an R134a high around 238F or lower.
R12 around 216

if you can achieve lower (reasonably lower) all the better, less
fatigue on the compressor.

Pressures are noted when the clutch is engaged.

When we say 90F, that is the average ambient air temp
entering the condenser (not what your local weather report has on your cell phone
nor the measurement over the grass in the next yard over)

Christopher Zach

Ok, some hard data. Temp at airport: 82F. Temp as reported by 2001 Prius sitting for several hours and turned to accessory: 87. Humidity: Extreme (sweating a lot). Wind speed 0.

• Car sitting for 2 days. Pressure was 90psi on low and high side. Partially empty can of R134a weighed in at 12.0 ounces with brass valve on a US postal digital scale. Brass valve weighs 2.5 ounces.
• Started car. Turned on front and rear AC to full, fans full. Pressure read 30 low/150 high at start, seemed to stabilize at 35/170 at idle.
• Added R134a, emptied can using bowl of warm water, stopped when can empty (warm). Removed can, can empty, weighed, 6 ounces. So added 6 oz of R134a, should be 30oz R134a in system.
• System read 50/210. Radiator fan was now on, sweat at the dryer.
• Revved up engine, dropped below 30's on low side, let go to idle, read 45/220.
• Turned off the engine, read 70/200. Removed high side and got a small spray of oil, so the system may have a bit too much oil.
• Experiment ended, engine shut down.

I think at the moment the statement "the compressor ships without oil" might be in error. The compressor had plates on the suction and discharge side, and I think they filled it with the proper amount of oil. So I may be running the system with an extra 4 oz of oil, which is not great, but at least the system will not seize up :-). Next time I'll check the compressor and see if there was oil in it, it did gurgle when I turned the pulley after putting the fittings on.

According to a real simple chart at http://rechargeac.com/how-to/ac-system-pressure-chart , the pressure at 85F should be: 85°F (29°C)45-55 psi / 310-379 kPa225-250 psi / 1551-1724 kPa.

So I'm a little low on the low side, and a little low on the high. Question is: Is this chart bunk? Car interior is not blowing super cold, but comfortable, with rear AC a bit cooler feeling than front AC. Maybe I'll get my IR thermometer and check that as well.

Yours for better measurement.

Christopher Zach

Also, my car does not have an AC sticker on the door or in the engine compartment, is is someplace special?
And what is the best way to measure ambient air temp? Cloudy day here, so no direct sun.

Thanks for the cross-checking of my numbers.

Speedtoys

If there was only a procedure written down by Porsche on how to do this...