Wild Bill

Thanks Ed I read that too and did that just after putting the initial oil in. BTW - although it may not sound like it, I followed the directions given at:

http://www.aircondition.com/tech/que...ing-Procedures

My crusty old gauge set apparently was the culprit in giving me the false readings. I checked it for leaks with my vacuum pump, but it clearly has issues.

Ed Scherer

BTW, one thing I screwed up when I did my system that I'm still not entirely recovered from: I had my gauge set and hoses hooked up to the low and high sides when I first started the car after a fresh load of oil in the compressor and one 14 oz. can of R-12 liquid-filled into the high-side.

Later, after completing charging (remaining amounts gas-filled into the low-side), all was well and everything was working just great.

But... when I disconnected the high-side hose, I got a good blast of oil out of the high-side hose. Lots of oil. Reflecting on that, it's pretty obvious what happened. Lots of oil sitting on discharge side (hose, lines, whatever) of compressor before the high-side port before starting the engine. Of course, some of that then got pumped into the high-side service hose, which, of course, was never really used for anything else (other than pressure readings) once I switched to low-side gas filling. So... that oil (along with a little refrigerant) got blown back out the hose when I disconnected it. Unfortunate, because I had no idea how much oil that was. I wound up injecting some more oil (almost certainly too much) the next day, after which the efficiency went down. I now have too much (and an unknown) quantity of oil in the system, so I'm going to flush and re-oil and recharge it again next time I get a chance.

Moral of the story: when you've got a bunch of fresh oil on the discharge side of the compressor, run the system a little while with an initial charge of refrigerant before hooking up your high side service hose!

(I'd be interested to know if anyone else has ever done this. Just so I can feel better about not being the only bonehead to do this. )

dprantl

The above is why I just disconnect the high-side completely from the car before starting it and running the compressor and charging from the low side. If you are charging by weight, there really is no point looking at the high-side pressure unless something is wrong. In which case, after the system has the correct refrigerant weight, shut off the car, plug in the high side and diagnose.

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

Ed Scherer

One other aside: I got a couple of nifty tools while doing my A/C system overhaul. Things that you think "should exist," and then you discover they do: a little tool that lets you change R-12 valve cores on a charged system (that tool was already used to change a slightly leaky valve on Brent's '91 GT), and a tool you can use to inject oil or dye into a charged system (which I used to inject oil after losing some in my "high side hose disconnect oil spray" incident. It's a real time saver to be able to do this stuff on a charged system.

Wild Bill

Do tell Ed, where did you get these handy devices? Sounds like something I could use!

Ed Scherer

Yeah, being an inexperienced, somewhat ignorant shade-tree mechanic like me certainly has its disadvantages at times... But I try to learn from the (frequent) mistakes. And even submit them for entertainment (or is it education?) purposes from time to time.

dprantl

Don't worry, same thing happened to my brother. I usually let him do it first

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

Ed Scherer

First one is easy and probably locally available for most people:

NAPA 783702 A/C Oil & Dye Injector





Second one (or somebody's version of it) might be available at NAPA, too. I got a MasterCool 91490



but I think NAPA has equivalents like NAPA 781099. They've also got this nice kit 783219 for both R-12 and R-134a valve cores.

This stuff is rather expensive, but given the time savings they can provide, well worth it (IMHO).



Also, NAPA had R-12 valve cores, too. Somewhere in the $1 to $2 range, as I recall.

911tracker85

good thread.

I am about to attack an inoperable AC on my 84 928. I bought the car late last year and the PO said the AC was working. when I picked it up, briefly turned on the AC and it seemed to blow cold. unfortunately I did not look under hood at the time to verify compressor engaged, but from the interior sounded like it did.

I checked the various switches in the system to find the compressor kicks on when I jumper the low pressure switch.

when about to try to put in some R12, find there is NO prssure in the system. I have checked all the accessible connections and cannot find any clear indication of source of leak. about to do a vacum/evacuation. if it holds vacum will put in a couple cans.

my big question is compressor oil. since I have not opened the system, should I add any oil when I charge it? I plan to add a little dye so I can identify the source of the leak if there is one other than the old hoses.

dprantl

Unless there was/is a large leak, the system should still have almost all of the oil in it, so I wouldn't add any.

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

Bill Ball

If you need the seals for the end of the R12 gauge hoses, look here:

http://www.tooltopia.com/index.asp?P...googlebase_18u

pcar928fan

Bill glad you have A/C again... You NEED it around here these days! Crap it has been HOT! We need TONS of rain and a break from the heat!