mj1pate

I thought of piggy backing this on an existing thread, but my need is very specific.
I'm also going through an AC re-activation in my 86.5. The system was open to atmospheric for years.
The compressor, rear evap, front evap, condenser were all vacuum tested, while disconnected in isolation. Vacuum hold at 30 was very satisfactory for each.
I’ve replaced every oring and exp valve in the system, so every connection was opened up.
The system is now fully closed with a sacrificial drier in place.
The system will not hold either vacuum (30 in-hg) or air pressure (120psi). It must be a pretty good leak, as either pressure begins drawing down immediately, fully down within 15 minutes.
Every joint is still exposed for testing and every joint passes Big-Blu bubble tests (with 120 psi).
A mechanics non-amplified stethoscope picks up no gas escape hissing at any joint, or in the cavity in front of the front evap.
Stumped I am.
Of course the hidden flex hose-metal junctions of the pressure/suction hoses along the pass fender are possible suspects.
Can anyone recommend a workable amplified stethoscope, capable of picking up the high frequency sounds of escaping air? Some such equipment in Amazon gets mixed reviews. I’m going to need some audio amplification help to locate this.
thanks!

Kevin in Atlanta

You might want to try and pressurize the system with CO2.

That is more effective in finding leaks.

Kevin

mj1pate

Hi Kevin;
I thought about using nitrogen, or maybe CO2 but air was cheap and a sacrificial drier was only $32. I just needed a gas to create pressure. I will add I’m using 2-stage dried air. I was SURE bubble testing and a mechanics stethoscope would locate a leak and discovered I was wrong.

Rob Edwards

Compressor shaft seal leak and it's just obscured by the clutch assembly so that you can't hear it or bubble test it? Or the evaporator core? Did you pull a vacuum on the system pre-re-oringing to see where the leak was (Not that anyone would have thought to do that, certainly not me....)

mj1pate

Hey Rob, I can’t rule anything out EXCEPT all the oring junctions and exp valve fittings; exhaustively tested .
The compressor was pre-install tested via vacuum applied to its local Shrader valve fittings and passed. The front evap help vacuum while the exp valve was removed.
Yes, even these items may have a hidden culprit. So, I need an instrument beyond bubble testing and basic stethoscope.

mj1pate

Ok… I found the leak, with the plain, non-amplified mechanics stethoscope.
The leak is in either the pressure or suction line running along the pass fender. I pushed the long stethoscope extension down into the fender area where the hoses run and could hear air movement that can’t hear anywhere else. I haven’t pulled everything along the inside fender apart to locate which hose is the offender because I haven’t the skills to repair either hose,
Does anyone in the Maryland or central/east PA area have these skills? I’m not looking for “ free” help. I’ll happily pay.
​​​​​​…..Mr Merlin?

at some point in the next few weeks I’ll pull “stuff” out of the inner fender well area and see if I can patch over hose leak so that I can pull and hold vacuum to (finally) get atmosphere out of the system until it is repaired.

Rob Edwards

Best case scenario is you have a bad schrader valve in the suction line, which is easily replaceable in situ. Worse would be the rear end of the rubber section of the high pressure line. Where exactly are you hearing.the hissing along where the hoses run? Here's an '86.5 right engine compartment for comparison.

FredR

Chances are your problem is the high pressure line- there is a short section of captive hose that is difficult to replace in-situ with the engine in the car and thus tends not to get replaced even during conversion to R134. Generally this is not a problem as long as it holds pressure - the exposure to mineral oil causes it to saturate into the hose and thus act as a barrier when exposed to R134.

There are workarounds to this problem- someone simply ran a hose from the filter drier through to the expanaion valve. If you have a rear ac this complicates matters. There are also some proprietary compression fittings that you could try by cutting into the line before it bifurcates. The purists do not like such- I am a bit more open minded about such- if they did not work then why would they be made? If I were stuck I would certainly give such a try.

You should be able to find the leakage point you describe by simply spraying soap solution on the line and watch for the bubbles.

mj1pate

Hey Rob,
The suction line Schaefer as well as the compressor schraders have all recently been replaced. The new (sacrificial) drier of course has a new schrader.
The moving air sound is evident down below the shock tower.

mj1pate

Hi Fred, well I have a leak and I’m not going hoist the engine for this, so hose replacement with OEM is not an option.
Therefore the humble author has no issues with a fitting type replacement/fix. Worst case, I’ll still have a leak.

Rob Edwards

Huh. It's all hardline along the shock tower. Maybe a normaclamp rubber failed and the line wore/vibrated through against the metal edge of the clamp?

mj1pate

hi Rob;
the region where I hear air movement is hidden until I remove lots of stuff along the fender well. The air sound is evident from the space behind (not including) where the pressure and suction lines bend near or around the radiator and the area in front of the shock tower. The most foreword (around the condenser) flex hose junction of the pressure hose is quiet.

FredR

Michael,

You can see the hose section on Rob's excellent photo- the transition is just behind the ignition coil. Why on earth they did not fit a union in that line is beyond me but nothing surprises me with these cars any more!

The repair methodology I mentioned is based on compression fittings made by an outfit called Dorman. To be clear I have not used them but have used similar products in the oil industry. Makes no difference whether the problem is in the hose or the hard line as long as the offending item is extracated.

mj1pate

Hi Fred;
see the picture below (hose #7) . Because of proximity, I suspect the the rear end of the pressure hose flex section is suspect. The front part (near the condenser) of the pressure flex hose is accessible and quiet.

FredR

That is the little bugger I would suspect unless and until proven otherwise. The poor little thing is nigh on 40 years old!

Normal operating pressure in that hose is around 225 psig