996Fever

Hi. I need some help troubleshooting my AC. 1986.5 928S Automatic. The other day my AC compressor clutch stopped engaging. My neighbor is an AC, but unfortunately not a 928 guy.

I have power at the fuse in position 8 and a good fuse. The AC button on the controller lights up when pushed with the fuse inserted, so I know power is making it that far.

I have no power at either pin on the pressure switch on the side of the dryer. I tested the pressure switch, and it is in the closed position as it should be. If I run power from the Jump port on the fender to either pin, the clutch kicks in and the AC is ice cold.

Also, it has a full charge. Once we figured out how to jumper it, he drew it down to a vacuum, and then we added a full 37 ounce R12 charge by weight just to make sure it had a 100% fill. So it's not a freon issue.

I just do not know the proper order to trouble shoot it or where to look. Any help is greatly appreciated.

Randy

1986.5 928s Automatic
2001 911 996 Cabriolet

SeanR

Check to see if you have power at the freeze switch. If not then chances are your HVAC control units internal relay has failed.

SwedeInSiam

Sounds like a freeze switch problem or most likely the relay inside the AC headunit.
https://rennlist.com/forums/928/6788...re-w-pics.html

996Fever

Thank you for your input. How hard is it to get at the freeze switch? Is that the one in the dash with the small vent thingy? And, if so, can you just pull it out of the dash to test/bypass it, or do I have to go at it some other way?
Thanks again
Randy

SwedeInSiam

The freeze switch is under the cover behind the air filter. See post #1 in the link I posted

hacker-pschorr

I have a feeling this is in my future with the 87 and I already have a relay (or 3) in the parts bin.


Side note.....is there an "easy" way to pressurize the A/C systems to check for leaks but also test the pressure switches? I know the typical method is to evacuate the system and see if it holds a vacuum, I always found this odd. The system needs to hold pressure not vacuum to function properly and I've seen more than one A/C system hold a perfect vacuum only to leak out all the freon once added. It seams like a better test would be using a compressor and regulator, bring the system up to the maximum intended pressure and check for leaks.

996Fever

Wow. Thank you Anders. That write up from Dwayne is spot on. I love a tutorial with lots of pics. I'm going to test the freeze switch tomorrow. Sad part is we 1/2 way pulled off that plastic sheet cover over it, before giving up because it was hard to pull out and we assumed it only had wiper linkage behind it. I'll be in there tomorrow! I'm 56 and I've had multiple Porsche's, but even my 930 didn't mean as much to me as this 928. The Shark has always been the best car ever to me, and the one I have now is very special.
Thank you all
Randy

996Fever

Thanks again Anders. Wow, my 928 looks almost like the one in your avatar right down to the rims.
Thank you again

hacker-pschorr

What kind of tires are those? Interesting tread pattern.

996Fever

They were some funky all season tires the 86 year old original owner Lawyer I bought it from put on it just in case the world would come to an end during winter and it would need to be driven. I replaced those 4 days after getting it (notice in the pic it still had it's temp plates on). He took awesome care of it and provided me with a 6 inch thick pile of maintenance receipts. Everything works perfect on the car with the exception of the cruise control only working when it feels like it. Interior is like new with not even a bit of dash pull by the vents. Even the tire compressor, bulb kit, and everything was there.

SwedeInSiam

Nice, which blue is your car. Looks a bit lighter than mine.

If you need to change the relay in the headunit and you can't find a relay to fit as in Dwayne's thread the you can do as I did. I just took the original relay out and soldered in wires to come out of the headunit and connected them to a normal Bosch relay. That will last forever.

hacker-pschorr

Makes sense, my first thought was snow tires except on chrome rims would be rather odd.

Carry on...I have a weird interest in tire tread design and wish I could get a "new" set of 80's vintage Goodyear Gatorbacks

dr bob

The system needs to be absolutely dry, so the easy answer is to use some dry nitrogen. Not the stuff you get at the tire store unless you start out with an evacuated (vacuum...) air tank, and their nitrogen has a dew point of -50ºF or so. The safest way to get the right nitrogen is to buy a small cylinder of it from a welding supply store, along with a regulator and some fittings that will let you connect to your gauge set and the car.

If you --really-- want to find --all-- the leaks, grab a cylinder of helium at the party supply store, and rent a helium gas detector to sniff the system. Helium atoms are, um, pretty small, and helium is rare enough in the atmosphere that a sniffer will find traces of it. When chasing down leaks in low-pressure systems, helium is the weapon of choice. We pull a vacuum on the system, set up the helium sniffer in the exhaust of the vacuum pump, then go fog all the connections and other possible leak spots with helium until the detector screams. If you can make your AC system helium-tight, you'll hove no trouble keeping the relatively-massive R12 molecules trapped inside.

Go with the nitrogen.

hacker-pschorr

Nitrogen sounds like a good plan.

I suppose propane and a lighter wouldn't be the best idea?

996Fever

Hi again. Mine is a 999 "paint to sample" color. He had it painted by Porsche to match an old 911 he had. It is in amazing condition for 30 years old and has larger than normal metal flake. It looks awesome, and reminds me of the color of my 69 Mustang Mach 1 I had 40 years ago.