Auto Air Conditioning & Heater Repair: Leaking A/C freon (r134), freon r134, dodge caravan

Question
Wayne,

Thanks for taking my question. I was hoping to not impose by searching FAQ's but didn't see any. I'm sure you've addressed this common issue before. My nephew's 2000 4-cyl Dodge Caravan's A/C won't hold freon/r134. My question is do ANY of the alleged aftermarket A/C leak "sealants" actually work and if so, what is the best one? I've tried the canned aerosol type freon that supposedly included a "sealant" but it was unsuccessful. Any ideas? We can't afford to take it into a shop for professional repair. Your help would be most appreciated.

Thanks!

Answer
Chris,

 I totally understand your situation with this Caravan.  Regardless of being able to afford to take it in for professional repairs I don't usually suggest making any major air conditioning repairs on vehicles more than 10 years old unless they are in exceptional condition.
 There are times as a professional I know when to 'pull the plug' or 'give her one last shot of adrenaline' and that is where you appear to be at with your vehicle.
 A 2000 Dodge Caravan with a 4 cylinder engine (rare in my parts, ours are all equipped with V6's) does not have an AC system known for its integrity. And choosing the right stop leak additive (or whether its a good candidate for it) is dependent on where the system is leaking.
 Evaporator failure, compressor failure and condenser failure are the most common areas on these vehicles.  If the Evaporator is leaking (dash removal is necessary to remove and replace) its a time consuming and expensive repair that is an excellent candidate for stop leak.  
 When an AC system is at rest pressures are approximately 70psi(depending on ambient temperature) and when it is running the system is divided into a low and a high side.  Those pressures on an HVALVE system such as yours with 134a will fluctuate from as low as 30psi on the low side and sometimes as high as 375 on the high side in heavy slow moving traffic.
 As you can imagine 375psi can be hard to seal with a stop leak and if it is a rotating member such as a compressor shaft seal to shaft leak the stop leak will not work anyway.
 The trick to getting stop leak to work is understanding how it works.  Any substance that hardens needs a catalyst to cure.  The catalyst that AC systems use is a little H20.  That H20 is all around us and when the sealant exudes out through the leak it hits the atmosphere and starts to harden.
 Here's where the problem is.  If you have a big leak, or the system was completely empty there is a good chance you have moisture in the AC system as well.  If you add stop leak it will cure inside of the AC unit before it has a chance to get out through the leak.  If there is a large amount of moisture that was not absorbed by the desiccant in the drier you may be setting yourself up for disaster.
 The best way to prep a system for stop leak is to put it on a 29" vacuum for a minimum of 30 min.  I usually let them sit on one for over an hour but 30 min is the industry standard.  This low pressure area causes all the moisture to boil off and you get a nice dry environment for the stop leak product.

Now to actually answer your question:

 I avoid the use of stop leak where I can but there are times I try to help people out.  I use a product manufactured by ClipLight.  If you pull a vacuum on a system and the evaporator is the leaking component, yes it definitely works and does not damage any components.  I would highly recommend that you label your system as containing stop leak now as it plays major havoc with our machines.  I have 3 AC machines, one for virgin systems, one for questionable ones and one for known contaminated ones to recover refrigerant for disposal and two refrigerant identifiers.
 Hope you found this helpful, be sure to wear protective gloves when handling AC products and most specifically safety glasses!

Wayne