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Find leaks in A/C

Discussion in 'Chevy Trucks' started by 75gmck25, Sep 18, 2003.

  1. 75gmck25

    75gmck25 Senior Member
    Messages: 119

    About a month ago I discharged and took apart my A/C ('75 GMC converted to R134) to replace a plugged orifice tube. But the A/C stopped working about a week later. When I finally checked it last week I found I was down to about 4 ounces of R134.

    We charged it up again, used an electronic leak detector, and found one fitting that needed to be tightened up. That was last Saturday, and it still worked okay on Monday (but the day was fairly cool anyway). However, when I turned it on Wednesday, I can't get any cool air any more. The compressor still cycles on, so its not low enough on r134 to engage the low pressure cutoff.

    I assume I'll find that it is still leaking R134, and I need a more effective way to find the leak. Is it a good idea to try some of the UV-dye based leak detectors instead of the electronic detector? Most of the parts stores sell a small can of leak detector that you can fill through the low side port. But I don't know how expensive it will be to get the UV light.


  2. wyldman

    wyldman Member
    Messages: 3,265

    You can get cheap UV lights,but they are garbage.I'd take it to a shop,and have them presuure test it with Nitrogen.You can get the pressures up higher,and find the leaks with soapy water.

    If that doesn't find anything,then refill it and inject the dye,and come back in a few days to have them inspect it.You can also double check the evaporator carefully with the sniffer.

    Did you change the hoses ? The older style hoses were terrible for conversions,as they are not a barrier type hose,and the crimping methods were poor.
  3. johngus

    johngus Senior Member
    Messages: 117

    In my shop we use the dye an dblack light only.It seems to find all the leaks for us.Now all our new cars come through with dye already installed in the motor oil and AC system.
  4. speedracer241

    speedracer241 Senior Member
    Messages: 325

    The guys I work for now have a modified manifold gauge. It is set up to force clean shop air into the AC system. Then usually you can listen for the leak. Sometimes you need a stethascope to listen around the compressor seals. That is the first choice.

    They also use the dye and black light too.

    Today we charged a system with r-134 with stopleak in it. Guess we'll see how well that works, couldn't find any leaks.

    Good luck,
    Mark K
  5. 75gmck25

    75gmck25 Senior Member
    Messages: 119

    I picked up a can of R134a with UV dye and stop leak (seal conditioner?) yesterday. I also bought one of the cheap Interdynamic gauges that has fittings for either the high or low side.

    I plan to put the gauge on the high side to track the pressure, and charge the system with the new can of R134. However, I don't want to get carried away with recharging and get too much R134 in it. It was running about 247 on the high side right after they charged it last weekend, so I figure that I don't want it to go to more than about 250-260.

  6. wyldman

    wyldman Member
    Messages: 3,265

    Most R134A systems (converted ones) will run much higher high side pressures than the old R12.On a really hot day,idling,you may see 280-300 on the high side.Adding an electric fan will help control them.If your topping up,just keep adding until your vent outlet temp stops dropping and stays steady at idle.You may see the high side go above 250-260.I wouldn't let it get any higher than 280 or so,or it may blow off some on hot days.Paying close attention to condensor cooling and airflow,and insulating the lines will make the system work better overall.
  7. Dave1250

    Dave1250 Member
    Messages: 57

    uv dye

    Hi you can look for oil on any lines that usually means a leak also spray the rubber lines and check them for small bubbles most tractors that I work on if I can not find a leak in the fittings or compressor shaft seal it is the hoses. hope this helps you out
  8. karl klein

    karl klein Senior Member
    Messages: 557

    you should try putting hotshot in it instead it will cool better than 134a in a r12 system and the molecules are larger so it wont leek as fastits called hot shot or r414b works great!!!!
  9. 75gmck25

    75gmck25 Senior Member
    Messages: 119

    I checked the pressures today, and after adding three 12 oz cans of R134 I have it up to about 242/42 psi and the A/C is working. One of the cans of R134a included UV dye, and I hope I can now use a blacklight to see what is leaking.

    By the way, I used one of the cheap Interdynamic kits to check pressure and recharge. It includes a gauge that can measure either high or low side pressures (it has two adapters), and a hose and tap to fill R134. The kit worked okay, but by the time I got 3 cans into the system the tap was already leaking around the packing nut. I tightened it up and the it stopped leaking, but the overall construction is not that good. The gauge and hose also take a beating because you end up switching it back and forth between adapters as you check pressures and fill R134.

  10. 75gmck25

    75gmck25 Senior Member
    Messages: 119

    I ran the A/C for a while with the UV dye in it, and after dark I used a cheap blacklight to look at the hoses and fittings.

    I found one fitting with a little residue on the bottom side, so that O-ring may not be completely sealing. However, I found a lot of residue when I ran the light over the hose from the compressor (muffler) to the condenser. It looks like R134 is seeping through the barrier hose. The hose set is only about a year old and is stenciled with the words "barrier hose", but its leaking somewhere. It looks like it might be a multi-layer hose, since the outside is a rough surface material that feels like the outside edge of a fan belt. I guess its also possible that a fitting is leaking between the hose layers.

    I cleaned the hose up and will check it again after about 24 hours to see if its still leaking. If this is the problem, would an A/C shop sell any better quality hoses than O'Reilly's or Autozone? For most auto parts it seems like everybody carries the same brand. Also, the leaking section is only about 18 inches long between fittings, so I could also get a shop to just replace that section of hose.