Backyard AC repair - Doing it the wrong way. -
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post #1 of 1 Old 05-04-2013, 08:00 PM Thread Starter
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2000 XJ Cherokee 
Join Date: Mar 2010
Location: Scottsdale, AZ
Posts: 677
Backyard AC repair - Doing it the wrong way.

Or the lazy way,.. whatever you like. What you can expect from using any kind of "leak stop" or "sealant" product. Understand I'm not bad-mouthing these products. This is just the normal result.

This story starts several years. so it's a long-term fix/test report. ('00 XJ, 4.0/AW-4 - stock) It concerns many of us because the leak I have is a common one on the XJ, and many of us keep these vehicles for years or decades.
Around summer/fall 2005, the AC developed a leak - it started cooling less and less, accompanied by the compressor short-cycling. Diagnosis revealed a low charge condition - low pressure switch causing the compressor to shut off shortly after it came on. The obvious first response was to slap in a can of -134 with leak detection dye and run it.
This "fix" lasted about two weeks. A close inspection of the under-hood components revealed,.. no visible dye,.. crap. The one AC component not visible under-hood is the evaporator core behind the dash, conveniently also the piece that tends to leak on an XJ AC system.
The proper fix is to pull the dash and replace the evap. core, but I'm a lazy guy. Knowing the service history of my XJ(no problems/never worked on or opened - that part is important) I dumped a can of leak sealant in the system, recharged it, and ran with it.
A lot of people don't like the sealant products, because many times the whole system stops working shortly after using the sealant. The problem stems from a misunderstanding about the AC system or ignorance about how the sealant works.
Two facts:
1 ) AC leak sealant reacts with moisture(water vapor) to seal small leaks when it's exposed to air as it leaks out of the pressurized systems.
2 ) There's ALWAYS some moisture inside the system. The desiccant will be slightly contaminated when new, and water is one of the byproducts of the normal break-down of the refrigerant(that's why there's a moisture filter/dryer in the system in the first place)
Inevitably, some of the sealant will react with the moisture inside the system. In badly contaminated systems, the resulting goo will clog up something important. If there was a lot of moisture in the system, the desiccant in the accumulator will be contaminated even if the system is later purged. The sealant will react immediately and clog up the filter dryer, resulting in a non working system.

I used sealant knowing my system had never been discharged, and never left "open" to outside air. There was (inevitably) some moisture in the accumulator, but probably not enough to cause an immediate problem. I was right about that. The sealant worked pretty good. Since adding it, I've had to add about 9oz of new refrigerant once every 18 months(there is still a very small leak), and its held that way for 7 years.

Last fall(2012), the system started cutting out again. Diagnosis showed it was cutting off due to overpressure on the high side. It wasn't low on refrigerant. The refrigerant wasn't cycling through the orifice tube or the accumulator fast enough and was causing the high-pressure cutoff to kick out when too much liquid built up in the high pressure lines. The sealant had finally clogged up something important.
I just spent $50.00 to have the system discharged, two hours of my time and $70.00 on an accumulator and orifice tube(NAPA), and I still haven't changed that stupid evaporator. Time will tell if the seal will hold with the new parts and refrigerant purge, or if I'll have to give in tear the dash down.

The whole point of this is to let you know - if you're planning to keep your Cherokee for the long haul this is a problem that needs to be fixed right the first time unless you don't mind re-visiting it on a regular basis.

Side note - if you plan to attempt any AC project involving the refrigerant system yourself, you need some specialized tools - Automotive refrig. gauge set, nitrogen tank/regulator, and a vacuum pump are all mandatory to get the system back up and running.

"Never attribute to malice that which can be adequately explained by stupidity, but don't rule out malice."
My other car is also a Jeep,.. and so is the other one,.. and that one too. How many do you own before it's "a herd" ?
tbburg is offline  

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