2000 Durango AC

My wife brought our vehicle in for an AC check last week as it was no longer blowing cold. The shop performed an electronic leak test and found no detectable leaks. They evacuated & recharged the system,
(including addition of sealant, oil & dye) and "cleaned debris" out of the compressor. The vehicle passed a 20 minute vacuum leak down test.
The AC worked great for about a week, then lost its cool almost immediately. The shop is now saying that a black light leak test has found dye on the evaporator core outlet indicating that a new core is needed - cost $1200.
The shop is claiming that sometimes a re-pressurized system will cause weak parts to fail (ie, evaporator core). I feel that they simply did a poor job of testing during the first visit, and charged for unnecessary services that didn't resolve the problem.
Would a core go that quickly without any warnings or indications during testing? Do you think a black light test done on the first visit would have identified the core as the problem?
Thanks
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It is not uncommon for a system to pass a vacuum leak down test but then leak when the system is under pressure.

I don't agree with that statement. It had a leak when you brought it in the first time, that's why it stopped working.
I feel that they simply did

Such as ????

The evaporator core was most likely leaking the first time the A/C stopped working. The evaporator is buried inside the heater box and usually not visible unless removed from the vehicle, this makes it very hard to diagnose a leaking core. It would be almost impossible to find the leak with a black light on the first visit as there would not be any dye in the system. Once the dye is added to the system it takes time for enough dye to leak out so that it can been seen with the black light. The smaller/ slower the leak the longer it takes for the dye to become visible. A leaking evaporator is the hardest type of leak to find. I would say that the shop who did the work followed normal diagnostic procedures.
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leak detectors will find false leaks and good parts can be replaced when not needed. Normally when dye is installed, the shop should recommend that you return in a week to see if any traces of dye can be found. (this should be done at a no charge to the customer when you bring it back). Normally the one time charge is an hour labor not including any failed parts found after the completion of the dye test. I have never heard of cleaning the debris out of the compressor, this was probably something they just told you to make it look as if they did something they didn't. If they did install a sealant, they may have caused more problems down the road. If the core is really bad it was bad when they first charged the system and just didn't find it. That was more then likely your leak that caused the a/c to quit the first time. Either way you would have had to pay for the initial charge. Just curious...how much did they charge you?
Glenn Beasley Chrysler Tech
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In article

If they performed the testing in that order, they probably wouldn't locate a leak electronically because there was not enough refrigerant in the system to begin with.

I hope you mean 'condenser.'

Depends on how they measured vacuum. A mechanical vacuum gauge is worthless. An electronic micron gauge probably would have alerted them to a leak but not shown them where it is. Few shops use or know of using a micron gauge.

Very plausible. If it turns out that the bottom of the evaporator is coated with leaves and other organic plant like debris, you have no one but yourself to blame for the failure.

Locating a leak, especially an evaporator leak is a bit tricky. Their procedures are not a bit outside the norm.

What do you mean "that quickly?" It was already leaking when you first visited them last week. Why do you think the A/C wasn't cooling to begin with?

It did. The dye is useless if there is no refrigerant to carry it/if the system pressure is so low that the compressor won't engage in order to circulate the dye. Normal procedure on an empty system typically is, recover, evacuate and recharge system, check for leaks with an electronic sniffer, if none are found, add dye and send customer on their way with the advice that a follow-up visit is likely necessary to inspect for dye escaping the system.
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