A/C leaking refrigerant,where are the most common leaks
 

I have a 89 Cab and this what I have done,As a HVAC TECH I know a thing or two about refrigerant. Last year I did the following:

• Filled system with Dry nitrogen to about 100lb standing

• then took soap bubbles and soaked every fitting,the hose lines under the car,the Evaporator,TXV,Condensers and found nothing.

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• I then left the Nitrogen over night and the pressure did go down maybe 10-15Lb cant remember exact.
  
• I pulled a nice deep vaccume and charged system to Specs.
• The A/C was nice and cold but every year I lose 1/2 the charge.

So I wanted to ask if any one can tell me where the common leaks are located before I add 134A again to the system again.
Thanks for your help..

Do you use modern Barrier Hoses?

If not, that is likely where your leak is. With R12 they worked much better. With R134a they will allow the refrigerant to seep out over time. Buy a set of Barrier hoses from Rennaire or Griffiths and report back...

The first thing I would do is add a Hi/Lo pressure switch ($15-20) to shut down the compressor if the pressure exceeds a "safe" value.

When you charged the system with nitrogen the gas cooled overnight.

Same Problem
 

I have the identical problem with my '89. No one can find a leak. I have about the same amount of leak down over a year period also. The barrier hose solution may very well be the answer.

Also, how do you install the hi/lo switch? Is it purely electrical or do I need to evacuate the system and refill after installing a hose with some sort of hi/lo pressure sensor in it?

WWEST....can you provide more info on the Hi/lo pressure switch. Link to where to buy.

Thanks...

This is why a standing pressure test is not really all that accurate. P1V1T2=P2V2T1
A standing vacuum test is more accurate. The downside to it is that you end up pulling non condensables into the system. Not a huge deal, but the moisture that comes in with it can be. If you are going to pressure up for a leak check, here it is still legal to pressure up with an HFC refrigerant to 100#. Problem is that you are required to recover that refrigerant too!
Sounds like you have a pretty small leak. While it would be great to find it to fix it, you would be into it for a few dollars by the time you are done.
I once worked on an air cooled screw chiller package that lost refrigerant every winter. Found and repaired several small leaks on the system but I always suspected that there was a leak created every winter when temperatures dip quite low. When the outdoor temperature would come back up the leak was next to impossible to find.

Have you checked your evaporator? If they didn't switch to the barrier hoses when your system was converted to r134 you are losing gas through the hoses.

I will look into this..thanks

I did check the Evap,I think I need to switch to Barrier hoses.. I will look into this.

I agree with the temp goes up pressure goes up. I think I need to switch to Barrier hoses..
Any Info on Hi/lo switch

Sorry I forgot to mention that on the Vacuum test I did lose pressure after a few hours,But not much and didn't let it stay all night,either way I think I need to look into the new Hoses..
PS.Those screw drives are loud whining SOB..

The older ones are particularly nasty! Newer units can be pretty quiet under load.
It is amazing how physically fatiguing it can be to work in a noisy environment. I would wear plugs and a headset in some of those rooms.
Try nitrogenizing with some trace gas and use a good electronic.

the best way to check for leaks is with a vacuum gage. you should be able to pull a vacuum down to 500-700 microns and hold it. that also tells you all the moisture is out of the system.
if it will not hold, you have a leak.

Digital Vacuum Gauge, Electronic Vacuum Gauge, Vacuum Pressure Gage

When I had a mystery leak it ended up being right at the compressor manifold. Since that is where the charge ports are the electronic sensor always sensed some residual or so I thought.

I find it interesting that some AC experts love the dye & black light method to find a leak and others experts say never put dye into the system. I wish I had a definitive answer.

Slow Learner... Please clarify
 

Sorry for being a slow learner here. I need some clarification to WWest's post with the hi/lo parts link.

My '89 a/c ports have been retrofitted to R134a. My understanding is that in the process of installing the R134 ports they are sealed in place and cannot be removed once installed. Maybe I'm wrong here.

In any event, my question is "Can I install the binary hi/lo cut off switch listed in WWest's post directly over the retrofitted R134 ports?". Or do they only fit over the original R12 ports?

Also, if I can remove the R134 ports does the system need to be evacuated first before installing the switch?

Thanks for the link!! I've been paying a hell of a lot more than that locally!!:(:(

Yes!!

^ My answers showed up in your quote, sorry..

Typically at the compressor shaft seal, but "typically" doesn't apply to anyone specifically. As suggested (I think), fill system with a small qty. of refrigerant, then check the usual hose/system connections and components with an electronic sniffer.

Sherwood