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A/C stop leak

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I recently bought an A/C recovery machine. I've heard plenty of horror stories of these machines being destroyed with stop leak.  I spent the money on a "stop leak" detection kit. Just had a car come in my shop that is full of stop leak.  Didn't even move the ball in the test kit.  Asked customer about it and they have been putting in cans of freon from every source around for months.  I'm sure some with stop leak.  Obviously it's not working as the system is still leaking. My question is how do other shops handle customers that have tried this cheap do it yourself fix, failed... and then put my investment in equipment at risk?  Replace everything in the A/C system?  Is there some kind of flush that will remove that cr**p?  Call the customer and tell them it's now a winter vehicle only?  Not sure where to go in this situation and can't really seem to find an answer on the almighty google thing.


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I can't speak with great authority, maybe I can point you in a general direction.   I purposely selected my RRR machine (CPS FX134a) because it uses ball valves instead of solenoid valves and is much less prone to sealant damage.  Downside is there are way more techs that can repair Robinair machines than CPS.    AirSept makes a filter, called RecycleGuard, that filters out sealants.  One of these filters can be seen here:  https://airsept.com/Products/Details/12  

With sealants, there is a seal swelling kind and a hardening kind.  I think, but don't know, that most sealants sold today are the swelling version.   The test kits should be able to test for the type of sealant.   If the sealants are the reason for the failure, then replace everything (lines and all) is the solution.  Otherwise it repeats the cycle after repair.   It seems that only the hardening sealers are the machine killers.

I've been looking for clear answers on the risks of proceeding with seal swellers, but there's no consensus.   In other technical HVAC forums, I've seen the debate rage from change it all to flush the heck out of it and use the RecycleGuard to protect your machine.  

If you proceed, at least document the risks that the Stop Leak may cause a future unwarrantied outage.   For sure, I wouldn't do this without changing compressor, condenser and expansion valve.  Then flush the evaporator and lines thoroughly.  Hope this helps a little.

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Well... I thought I had ordered one.  Just got notice that they don't have them in stock and have no idea if or when they will be able to get them. Will try to contact the company directly in the morning. Robinair shows a similar product, but it lists as discontinued everywhere I can find.  


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  • 3 weeks later...
2 hours ago, coastalcarcarenc said:

We always ask if they have added any refrigerant themselves, if so we ask to see the can to check for sealer. If it does have sealer we do no service them due to the possible damage that can occur to our a/c machine. 

I use this kit on every system.  The one I had that proved to have sealant I asked the customer about it and he was sure he had never put stop leak in the system. They had added canned refrigerant themselves several times, but the leak had gotten bad enough it only lasted a day or two.  He wasn't aware that about half those walmart cans have stop leak in them.  I don't trust the customer with my equipment investment, and even if they meant no harm, there is no way to know if my customers kid or husband or even another shop had ever added the stuff.  I highly recommend this kit.  https://rotunda.service-solutions.com/en-US/Pages/ItemDetail.aspx?itemID=122683#:~:text=Neutronics QuickDetect™ A%2FC,before attempting recovery or repair.&text=Sealants can void warranty.


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  • 2 weeks later...

I use a Yellow Jacket "trap" (38080) on every car I recover. I'm running a Robinair 34788 NI-H and have not had any trouble in 5 years.

I recover from low side ONLY (less oil come out) and the trap has not missed a drop. The machine never recovers oil. 

I intentionally recover my own cars without the trap to test the machine once a year. Oil recovery works fine then. The machine needs a tiny amount of oil to keep the solenoid seals lubricated.

I believe 90% of the vehicles I service have sealant in them. The little test kits are not worth the trouble IMO. I do not use them. They are not accurate enough for me and take too long to test.

It is difficult to find straight refrigerant in the DIY auto stores. Almost everything has oil and sealant...

I have NEVER seen the sealant fix a leak but I have seen the sealant take systems out. The usual culprit is a membrane that the American manufactures like to use as a debris screen.

The tiny holes in the membrane get clogged with the sealant and you find ALL of the oil in the system on the feed side of this membrane. GM SUVs with rear AC are the worst culprits.

The tiny screen is inside the liquid line at the bulkhead fitting in the rear. Most techs don't know it's there as it is not a normally changed part (and it should be). A Murray part # for the little screen is 39335.

It looks like a 1/4 scale orifice tube screen. The liquid line front to back has enough volume for the entire oil charge. If you have a plugged one and you don't change it you will have a comeback within a year. Rear AC will be wimpy as well.

GM condensers with a replaceable dryer cartridge (Cadillac SRX) also have a super tiny membrane inside the dryer that will clog. Symptoms are low pressures on both sides, piss poor cooling, and a viciously hot discharge line. There is a TSB regarding this.

If you refuse to service your customers cars because they might have sealant you are destroying your relationship with those customers. We have to service the systems and educate the customer.


Occasionally I hit a system that has been massively over oiled. The sealant is everywhere. I will commonly replace compressor, condenser, orifice/TXV, dryer/accumulator, and discharge line. I will over flush remaining lines and evaporator and offer NO warranty.

I haven't had a comeback on ANY of those but I believe I have been lucky.

Customers will seldom pay to have the entire system replaced and see the shop as an "over charger". They will not come back to you for the other things they need.


My Robinair machine's manual states "any leak sealers found inside the machine voids all warranties"...

I run a shop in Texas that specializes in AC repairs.


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I bet you have a bunch more heater repairs than I do...

One thing I left out.

My machine has a line flushing feature for use with hybrids. It burns 1.5 lbs of filter life (limited by Robinair to 150 lbs before filter change).

I do use this feature when I hit a bad one AFTER I'm done with the job.

I clear the lines immediately after I'm finished...

One thing that's cool is when I get a a massively over oiled one and the trap has 8 oz of oil in it the oil bubbles like a coke for 2-3 hours and the 8oz drops to 6oz

The oil has liquid refrigerant in it.

This phenomenon is useful when you have to open a system. It will "out gas" for a couple of hours AFTER recovery.

If you tightly plug the lines it will "pop" when you pull the plugs days later, sometimes it will blow the plugs off (bad). Often I will use a balloon on one side to allow for expansion.

If your system is outgassing when you plug it and the plugs stay in the dryer does not get poisoned with ambient humidity and I will commonly re-use the dryer.

If I can I leave the systems in vacuum overnight (machine hooked up but turned off) and re-pull in the AM. This vastly reduces the moisture in the system.


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  • Have you checked out Joe's Latest Blog?

      It always amazes me when I hear about a technician who quits one repair shop to go work at another shop for less money. I know you have heard of this too, and you’ve probably asked yourself, “Can this be true? And Why?” The answer rests within the culture of the company. More specifically, the boss, manager, or a toxic work environment literally pushed the technician out the door.
      While money and benefits tend to attract people to a company, it won’t keep them there. When a technician begins to look over the fence for greener grass, that is usually a sign that something is wrong within the workplace. It also means that his or her heart is probably already gone. If the issue is not resolved, no amount of money will keep that technician for the long term. The heart is always the first to leave. The last thing that leaves is the technician’s toolbox.
      Shop owners: Focus more on employee retention than acquisition. This is not to say that you should not be constantly recruiting. You should. What it does means is that once you hire someone, your job isn’t over, that’s when it begins. Get to know your technicians. Build strong relationships. Have frequent one-on-ones. Engage in meaningful conversation. Find what truly motivates your technicians. You may be surprised that while money is a motivator, it’s usually not the prime motivator.
      One last thing; the cost of technician turnover can be financially devastating. It also affects shop morale. Do all you can to create a workplace where technicians feel they are respected, recognized, and know that their work contributes to the overall success of the company. This will lead to improved morale and team spirit. Remember, when you see a technician’s toolbox rolling out of the bay on its way to another shop, the heart was most likely gone long before that.
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