jbrob007

We just recharged the A/C system with R134a on my 86.5 / S3. All seemed to go as planned and the A/C was nice & cold. When I got home I heard the sound of leaking air under pressure coming from inside the engine compartment on the passenger side. I saw what I believe to be refrigerant venting from a hard pipe just behind the A/C low side nipple (black cap). It wasnt coming from the nipple. There are two hard lines back there - one from the A/C low side nipple that runs aft towards the cabin and another running above it (covered in black rubber insulation) going to the forward A/C radiator (black one). I couldnt tell which line the venting originated from as its pretty tight in there and the engine was HOT After I picked up my jaw off the floor I restarted the car and the leak had stopped. Took the car for an extended drive with A/C on full blast and it was nice & cold. When I got home there wasnt any leak detected - NONE.

Does this car have a pressure relief valve (PRV) on the A/C system??? If not, what's happening? I'm stumped... which is pretty easy to do

griffiths

I don't believe there is an ac blow off valve on that side.
If the car was charged properly and everything is working properly (such as condenser blower motor), then there would be no blow off. If the low side service port had a sticky schrader valve and then it seated after you turned off the car... maybe.

Take a picture of the general area and paste an arrow to where you thing
the leak was coming from and post it in this thread.

jbrob007

If I knew how to post an arrow I would... a description will have to suffice. At first glance, it appeared to be coming from the naked / uninsulated (shiny) line coming from the schrader valve (black cap). Then I noticed there were TWO A/C lines... the black rubber insulated line is above the shiny line to the schrader valve. Felt around, but didnt find anything obvious and couldnt determine which line was the culprit... cant see crap in there either - pretty tight fit...

You'd think the A/C system would have blown off all the R-134a refrigerant and the A/C would get warm if a line was compromised... So far my A/C is still cold... Hmmmmm...???

jbrob007

This one has more light... Unfortunately, the picture is standing on end... The coil is in the middle of the pic. Just to its left is the rubber insulated line. To the left of that line is the uninsulated (shiny) line leading to the backside of the Schrader valve (black cap). Dont see any kind of PRV, but ya never know whats stuck back in there.

Bill Ball

Deleted - sorry not relevant.

griffiths

There are 2 methods to check for a leak.

1) Refrigerant dye is injected in the system, you run the system for say 20 minutes or so to circulate the dye/oil through the system and then check with a black light. Sometimes you have to run the system longer, hours, before the dye will appear.

2) Electronic leak detector - quick and simple.

Whats going on here?

jbrob007

Just smudges from my fingers... The leak appeared to be coming from where it looks like the two A/C lines are tie-wrapped together. See where the bottom of the coil bracket & coil wire are wet... Probably the first place to look is the backside of those two A/C lines just below the coil.

Soooo I'm guessin' there isnt a Pressure Relief Valve in this location...?? Damn...

griffiths

Not that I've ever seen.
Look at the Porsche schematic, if there is a pressure blow off and its
not part of another component, such as the drier, then it would have
a item number on the PET and a part number.

Time for a electronic leak sniffer or dye.

jbrob007

Yep... time to look at the PET. Your probably right considering no one else has chimed in about the possibility of a PRV - especially in this location. I'll take a look. If the A/C has drained overnight - that'll tell me what I need to know as well... Gotta love it - just in time for summer

Thanks again!

Bill Ball

There is no pressure relief valve - just a high pressure safety switch on later models.

What I deleted above was the likeliest leak spot - the high pressure line that runs below the low pressure one. There is a hose section from the drier that ends right in that area bonded to the hard metal line that runs back to the expansion valve(s). I deleted what I wrote earlier because it made no sense that it would leak then stop like that. But, besides all the o-ringed joints and the compressor, that is one of the most common leak points. And it's one of the trickiest to repair. There was a nice thread on this repair.

https://rennlist.com/forums/928-foru...ion-stuck.html

It can be repaired w/o complete removal. However, some shops just bypass this line with a new hose run over the cam cover. Search "high pressure AC line" and you will find other options.

Like I said, I deleted my first post because you reported the AC worked after a partial leak. Still, this is where I would look. It's very hard to even see this line from above or below.

dr bob

For your pre-S4 R-134a conversion, condenser/radiator fan performance is critical. R-134a will have somewhat higher condenser pressures at the same condensing temperature. At ambients above 95º F, the high-side pressures spike more steeply than R-12, so extra protection is needed. The later (S4+) pressure safety switches offer both low- and high-pressure protection. The switch used on late-'93-on GTS cars is the best option, with a switch that's specifically intended to R-134a. The late GTS switch uses a different electrical connector, so you'll get to make a little jumper and splice on a couple spade terminals to get both switch contacts in the loop. It will help prevent destructive failuires of the compressor, and the hose and metal line connections in the high pressure side of the system.

The only programmed pressure relief I'm aware of is a blowout plug on the drier. It's a one-time relief, and IIRC it's somewhere in the 450 PSI plus range. It's a "feature" you really don't want to discover on your own car.

jbrob007

Bill, I think your talking about the same line as I am... Very hard to see ANYTHING much less get at it... If its not that line, then its the low pressure line above it - one of them gave out. Just gotta get in there and deal with it I guess. Gonna take her out for another run today to see if she's still cooling. Either way, it looks like I'll be adding to Roger's childrens college fund... again...

Thanks guys!

Alan

You do need a high pressure switch for the compressor clutch - the stock GTS R134a switch is best. as Dr bob says.

If you lose the cooling fans you will see a huge spike in high side pressure on R134a - that you wont get on R12 - enough to blow out almost anything if uncontrolled...

The GTS switch high limit is set to about 450 PSI for off and on again at about 365 PSI

Even 450 PSI is commonly enough to induce leaks

Alan

griffiths

"We just recharged the A/C system with R134a on my 86.5 / S3. All seemed to go as planned and the A/C was nice & cold. When I got home I heard the sound of leaking air under pressure coming from inside the engine compartment on the passenger side".

On occasion I have seen a 'leak' from either an R12 service port or R134a service port's schrader valve "after" the system is charge and usually caused by the schrader valve not seating properly. You can also have leaks between the R134a service port adapter attached to the old R12 service port. Just... a thought.

I believe your model year has a high side pressure switch, 928-606-150-00, attached to the inside port manifold on the drier, and the rating on the switch is 0-25 bar or 0-362 nominal psi (a more preferred high side cut off).

dr bob

Griff's post made me think of a point I missed. The charge adapter for R-134a fits over the original port/fitting, but the original Schraeder valve must be removed before the new port adapter is installed. The new fittings usually seal with a very thin o-ring that fits against the flared top of the old fitting. If the old Schraeder is not removed, there's risk that the pin will get bent over and interfere with the o-ring seal. If left installed, it interferes with getting correct pressure readings, and might lead to overcharging. Overcharging is dangerous on conversion cars, especially on pre-S4 cars that have primarily mechanical condenser cooling.