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It had to happen sooner or later. Something has gone south.
Sunday, the AC worked OK. It didn't freeze me out, but did get cold.
Monday, the AC didn't work at all. While changing the battery and ground strap, I did some quickie troubleshooting.
Pulling the wires off the freeze switch caused the idle speed to drop. Jumping the wires caused it to raise back up. This told me two things:
1) 12VDC was making it to the freeze switch from the control unit
2) The freeze switch was good
Tuesday, I put a test light on the AC compressor clutch connector in front of the passenger's side cam belt cover. The light did not light up with the AC button depressed. Note, the light in the AC button did illuminate when the button was depressed.
Today, I checked the refrigerant pressure in the system. That's easy. Big fat ZERO! Nothing on the High or Low side gauges. Thinking maybe my R134a hose adapters weren't depressing the schrader valves, I used a tiny screwdriver. The briefest of wisps of pressure came out of the high side fitting.
So, that is that...
I inspected the compressor as best I could from the top. I couldn't see squat from underneath. The Liftbars I ordered haven't arrived yet.
I saw no obvious damage to the compressor. The belt or pulley did not look damaged. I did not reach down and try to turn the compressor.
Looking under the front, the receiver/drier, low pressure switch, and high pressure switches looked OK. I saw no evidence of a leak.
So...I am faced with a major resealing at the least. This changes my priorities. Next weekend had been earmarked for servicing the transmission before SITM. The trans is fine for the moment and will wait. I will fix the AC instead. Fat man does not like being hot.
Here is my shopping list as of now:
-seal and O-ring kit
-receiver drier
I am hoping it is a failed O-ring or such, but we shall see.
I will be researching this, but I have questions now:
(Note: the PO had the AC system converted to R134a back in the early 2000's. He said everything was replaced but the compressor and hoses.)
-since this has been converted to R134a, which oil is more appropriate: PAO, PAG, or ester?
-what kind of WYAIT things do I need to consider?
-other than the AC hose that does not come out without the engine removed, what am I looking for that will cause me to tear my hair out?
That was my original intent if the system was just low. However for it to go from working one day, to being completely empty 3 days later, tells me that is a pretty significant leak.
I keep R134a in my shop, but I am not sure if I want to sacrifice it yet.
For giggles, I will put a vacuum on it and see what it pulls.
For what it is worth, I did not see any wetness around the clutch or body of the compressor. So, I don't think it is the shaft seal.
Also, while troubleshooting Monday, I jumped the wires together at the high pressure switch by the high pressure port on the receiver/drier.
The condenser cooling fan started running.
For what it's worth, my '85 is still r12.
I had it checked for a slow leak several years ago, the shop used dye and found no leak, but when they used the sniffer, they found the ever so faint leak behind the pulley of the compressor.
A vacuum pull and charge lasts for 2 years.
The compressor seal leak is fairly common on these, from what I have read.
I'm not specifically familiar with the pressure switches on the 86.5. On the later cars there's a separate switch for system low-pressure protection, mounted under the drier tubing manifold but facing up. Test that with your Ohm meter for switch open (low pressure).
Many "conversions" are less than complete. Old o-rings get left in, hoses are not replaced/rebuilt, etc. My to-do list has all the o-rings of course, including those at the fuel cooler, the rear air system including the solenoid under the passenger's seat and the pass-thru "bulkhead" fittings there as wellas the expansion valve o-rings in the rear AC console. The compressor manifold plates have O-rings underneath that I missed in my first conversion "effort" but discovered a day later when they failed catastrophically. There are at least six Schraeder valves that need to be upgraded. Two on the compressor, the two main charge/service ports that you have your hoses connected over, plus one under the low-pressure switch and another under the high-pressure (fan) switch. Those switches have o-rings too.
Put in new expansion valves, ones that have profiles better suited to R-134a. The valves will be in your hands to install new O-rings anyway.
For lubrication I recommend POE (ester) oil especially for conversions. For your previously-converted car you'll want to use whatever was used previously. POE has an advantage in R12 conversions since it "gets along" well with the mineral oil used originally with the R12. PAG is popular and is the ND oil recommended for the compressors, but also makes a nice jelly when it sees residual mineral oil. Unless you do a full chem flush, go with what was in the car last.
R-134a, for those playing along at home, has a sharper "spike" in the temp-vs-pressure profile that shows up someplace around 90º+ ambient temps in a balanced system. Overcharging the system makes this more acute, especially in a system that isn't sealed well -- the higher pressures will blow through old O-rings weakened by contact with new oils and refrigerants, or just tired with age.
For Seth's car, the sellers shop may have puffed a little too much refrigerant into the system, enough to find the weakest link, so to speak, in a seal or O-ring that has now failed. Hence the plan to replace ALL the O-rings and seals, not just the easy ones at the top front of the engine bay.
It's quite possible a fan may not be working well enough to keep pressures in check under severe heat and slow driving conditions. Things to think about as you move forward with your recovery work.
OTR18WHEELER: I am envious, Farris. EVERY vehicle I have ever owned had needed AC work.
dr bob: Thank you!!!
That was the kind of comprehensive advice I was looking for. This will give me something to work with as I get started researching.
I have already looked at PET to get an idea what is involved. I am no expert, but I have experience with automotive AC systems. I have already learned the hard way. You don't half-*** an AC system. You either do it right or not at all.
Here is my game plan:
-now: sift through the massive binder of receipts the PO gave me. I am betting there is something in there that will shed light on the scope of the R134a retrofit
Continue researching how to reseal the AC system on a 1986.5 928S without rear AC
-as soon as the Liftbars I ordered arrive, jack up the Red Witch and get a good look underneath. As well, search out the engine bay. I am looking for anything catastrophically wrong: IE blown up compressor or blown AC hose that I can't remove
-if I find no deal breakers, order parts:
All O-rings
All schrader valves
Any other seals
Correct expansion valve for 1986.5 with R134a
Correct receiver/drier for R134a
Low pressure switch
High pressure switch
Correct oil
Anything else we come up with...
Next weekend will be a thrash to repair the AC system. Compressor will come out to drain and measure the oil, then clean it.
Condenser may come out for the same reason. I don't know yet.
Good point, I plan on taking it all apart to replace seals and such. Do it today or do it tomorrow.
Ummm...yeah.
1) Greg is hell and gone across the country from me. Not exactly doable to send it to him.
2) Currently, Greg doesn't know me from a hole in the ground. Which is the same as he doesn't dislike me. What say we don't change that?
There is truly nothing odd or magical about 928 AC vs other "normal" car AC systems, except the hood badge. The compressor is fairly common ND, the expansion valves are shared with BMW and I think some M-B cars. The drier configuration is nothing exotic except that it's somewhat exclusive to Porsche as far as fittings and pipe routing. IIRC, the one supplied by DR way back when has a 944 part number, fits perfectly except that the dessicant can is slight taller and slightly thinner OD. A shim in the bracket and a shim underneath (to protect the power steering cooler) let it work perfectly. The fuel cooler, located on the front face of the firewall behind and slightly below the air cleaner housing, is an interesting and often-ignored feature of the system; it needs two o-rings where the lines attach, and stays loose from the firewall as you swap in the expansion valve seals.
Make Extra Sure the heat shields between the compressor and the exhaust manifold are installed by the time you are done. They can be a bit inconvenient to manage as you R&R the compressor. They do go in first with the compressor. Mark or Tom at 928 International will have used ones if yours are on the lamb after the previous "conversion".
When serviced right they hold their charge for a long time. Mine is just beginning to run a little low after 3 years in service after I replaced everything.
Redoing the system isn't particularly hard to do, just time and money consuming, so much so that most AC shops will not so much as look at a 928.
As others have said, make sure everything is replaced and refreshed. Do not half a** it. You wouldn't want to have to go in and replace a bad o ring you missed later.
I recommend removing the HVAC box from the inside of the car and resealing that as removing this is the easiest and best way to deal with the expansion valve.
Plus it gives you a chance to service the vacuum operated side of the system, which is a refresh all on its own.
05-11-2016, 12:54 PM
Today was not such a good day...AC kaput.
