borland

There are good a/c and poor a/c rebuilds. The only difference is how long they last.

ZEUS+

Poor ac rebuilds generally dont work at all due to the nature of the subject.

the flyin' scotsman

It has a large leak somewhere.............looses all pressure within a day or so of recharge.

As the car is now in its 19th year and its not going anywhere for 3-4 mths I have the time to look at the entire system hence the thinking of rebuilding the compressor, replacing the hoses, all 'o' rings, the expansion valve and the drier.

I want to do it once, do it well, and have good a/c for some years to come.

ZEUS+

Do you have access to dye and light equipment ? It is best to isolate the leak. Possible the front compressor seal due to age.

the flyin' scotsman

dye was put in the system on the last recharge in 2004. I don't have a black light and I cant get the system recharged for a while.........not that I really want to spend the money for it to leak out again.

The car is parked for the winter and as we live in a very rural area (read farm land) I would have to trailer the car to get in to the nearest auto dealer..........ain't gonna happen.

I'm ok with doing the entire system; I started this thread to ensure I don't miss anything not having much a/c experience before.

ZEUS+

Good idea. Just take into consideration 134 is is more tempermental than r12. Flush the system as borland suggested. The sight glass is of no use for charging. You must convert the capacity of r12 to 134. It will be less. Do not overcharge, 134 runs at higher pressures. Must be evacuated for minimum of 30 minutes. Just some tidbits for now.

danglerb

You can get a small black light (UV) sold for novelty use I suspect.
http://cgi.ebay.com/BLACK-LIGHT-STAI...575231QQihZ014

Did a quick search and decided to buy one for myself, $4.44 shipped in US, not sure about the frozen north. I suspect it is using a cold cathode type tube, so it may indeed not be a bright light at all, but suspect it works ok in enough darkness.

borland

Best way to learn is to buy and read the Haynes book "Automotive Heating & Air Conditioning".

Then hang out at one of the Automotive A/C forums. Read the FQA's there.

The UV light is for detecting gross leakage, before the repair/refurbishment. Not as a check before the fill. Professionals will use a thermistor vacuum gage to ensure the vacuum pump pulls enough vacuum to remove all water and flushing solvents, and as a check to ensure the system holds vacuum.

I have one of these:

http://www.omega.com/pptst/DVG-64.html

but this will also work well:

http://www.omega.com/ppt/pptsc.asp?ref=DVG-60

The manifold pressure gage set is inadequate to measure the vacuum levels needed to evacuate the system before the fill.

Richard Armstrong

I fix these in the uk. We are only allowed 134a so thats it, but I get 100% success. Your problem is knowing where the leak is - I use a special gas and overpressure with N2 then use a sniffer. Excellent results but a lot of kit for a one off. The dye is crap and will only tell you if you have a big leak, it gets everywhere and really pisses me off. Don't go there. If you want to pretty well guarantee a leak free system, you have to change the condenser, hoses, rebuild compressor, new expansion valve and new filter dryer. If you do all of that you have magically replaced all the 'o' rings too. The evaporators (in the cabin) rarely go, but if they do its a complete dash out job.
Most common leak points are the condenser mounting area (the bolt frets the bottom of the matrix and eventually wears through. No notice, but dramati, the metal to metal joint on the suction hose (engine side of the rad), the expansion valve adjustment 'o'ring on the later valves (S4) and the compressor seals. Seal kits are quite cheap and it is not rocket science, but dismantle the swash plate over a sucepan as ball bearings will fly everywhere. All the parts are available from SunAir. Very early 928s ('79 - 81)had Bosch/Behr compressors. Actually very good, but difficult to get bits for and very heavy. S,S2 and S4 up to '90/'91 use Denso 6E171, and '91-on use Denso 10PA20C. The 6E has 3 pistons, the 10PA has 5 and is lighter, and the hoses are almost twice the price and only available from Porsche - unless anyone else can tell me differently.

Re-gassing should be done by someone who understands the system as they are all slightly different, and although I start by putting a weight of gas in, the final adjustments are by experience. Don't ask me why, but thats the way it is. I have done about 25-30 systems now.

Richard

borland

Richard,

You don't need to buy hoses from Porsche. All the factory a/c hoses are non-metric (standard size a/c hose), so they can be rebuilt with proper hose crimping equipment.

All three engine bay hoses can be rebuilt utilizing the existing hose adapter fittings and standard size barrier hose.

However, for cars with rear a/c, the two rear a/c hoses are "reduced" sizes and can only be rebuilt with new hose barbs which require aluminum brazing.

griffiths

You most likely have a Nippondenso brand 6E171 model compressor.

A one day total leak down is a significant leak that usually can be found.
You could do a simple inspection for the common leaks in the 928, starting with
the high side hose (compressor to condenser) looking for signs of dirt collecting in the oil that may have been pushed out with the refrigerant; check closely where the hose is crimped (ferrules) to hose end fittings. Next, as Zeus suggested, consider a nose seal leak by looking again for dirt and oil accumulation around the clutch/pulley. The next suspect on a single evaporator shark is the expansion valve, however start your inspection at the drier and check for the rubber hose joint in this metal line prior to the expansion valve. When you get to the valve you are checking the inlet line port and also bellow “cap” on the valve; which we have found to be suspect at times.

If you have a friend nearby that has either dye & light detection tools or a refrigerant electronic sniffer this would be your next avenue to finding the leak. You could drop in a can of R134a and check out and sniff the system components and joints. Otherwise the last step is to simply pay a tech to find the leak and give you quote to repair.

If the source of the leak is the compressor, the 6E171, if not worn out (pistons, wobble plate, ball and shoes), is not too difficult to reseal. You can simply zip off the shaft nut in front of the clutch with an air gun, remove the clutch assembly with common snap ring pliers (watch the shims for setting the air gap in the clutch), tap out the key out of the shaft, remove the compressor assembly bolts with a 6 mm allen hex. They most likely will be residual ac refrigerant oil hiding in a cavity or two in the compressor. Before you clean it out inspect the oil using magnification to check for signs of metal contamination. If you find any they you most definitely want to liquid flush the lines, condenser and evaporator.

You’ll be replacing the front nose o-ring, center case halve o-ring, rear head o-ring and shaft seal, front and rear reed plate gaskets (if the compressor has not been resealed before then most likely these gaskets will be bonded to the reed plates; get some liquid gasket remover and be careful not scratch the mating surfaces on the nose and head. If the reed valves are pitted, corroded or rusted you’ll have to think about replacing them (not usually included in retail “seal kits”) if you can’t clean them up. The rusting or pitting is related to moisture in R12 systems.

Inspect your shaft where the nose seal makes contact with it. If it is rusted and depending upon how much pitting is present you maybe or may not be able to salvage the shaft. When you replace the shaft seal assembly note the orientation of the flats on seal assembly with respect to the flats on the shaft.

When you split the center section try to keep the shaft and pistons in either side or they will fall apart and leave you pondering for awhile, so keep the shaft with pistons on either side. Check the piston rings and the cylinder bores for wear, though not common a 6E171. Inspect the ball and shoes on the wobble plate as well as the wobble plate for excessive wear, again these items as not included in the typical retail seal kits.


The 6mm hex head assembly bolts are torque’d to 18 ft lbs. The air gap for the clutch should be checked, .020-.030" works nicely however you could stretch it to .040".

Overall you can reseal a 6E171 without dedicated tools if you take your time.

You’ll need to add refrigerant oil to the system and usually 6-8 oz works fine. Depending upon how old the drier is, what refrigerant oil you are using, signs of contamination, etc. you will probably want to replace the drier for good measure since you are going through all this effort.

When its time to charge the system, again you need equipment or a friend to work with you if they have it, otherwise just take it to your favorite ac tech (don’t forget to tell the tech how much oil you may or maynot have put back in the system). Evacuation times vary depending upon the system capacity, altitude and ambient air temp, however since you got all the time in the world I would suggest 1-2 hours. If you are converting to R134a or sticking with it, the general rule of thumb is about 85% of the original system weight of R12. However the final amount or adjustment is based on P&T (pressures and temperatures chart).

You may find some places on the net that sell seal kits out there and you may find a few posts here and there on the 6E171 R&R (alike model was used the 944 and the old Lincoln’s).

The two primary rubber hoses on a shark single evaporator system are the compressor and to condenser and compressor to evap pipe. I believe there is a short section of rubber hose in the drier to expansion valve however this does not leak often.

ROG100

Malcolm,
Is there any way you can stick with R12?
Or do I remember you or someone else in Canada saying it is unobtainable.
R12 here in the States is very cheap at about $15/20 a can. Cheaper if you can buy the larger canisters. I always stick with R12 on my cars.
Roger

the flyin' scotsman

R12 is not available in Canada and my system was coverted some years ago now to R134a by the local to me Porsche dealer.

Subsequent to the conversion the system has been filled twice; the first refill lasted perhaps a week, the 2nd a day or 2 max..........so the leak(s) are getting worse.

I've several projects to do this winter but after the tbelt change this is my next priority. Even up here mid summer temps make the car very hot to drive and yes I have the hot water valve wired shut.

the flyin' scotsman

You coming over anytime soon Richard?

Spring time in the Canadian Rockies vs the rains of jolly old

the flyin' scotsman

Thanks for the lengthy explanation.