after years of sub-par AC performance in my 2008 grand caravan (3.8L, dual HVAC units) my AC system started hissing at me (a clear sign of low refrigerant, right?). after my AC finally went out and didn't blow cold at all, i put in some dye to find the leak. using the black light, it looks like the leak is at the point where the rear lines meet the rear HVAC units thermal bypass valve (TXV). the entire TXV was glowing under the black light, but unfortunately i'm not sure if it was a broken TXV, or bad line connections, or a bad line seal, or...

i have only a little AC experience (although this year i seem to be gaining more and more *rolls eyes*), so i'm not really sure the best way to go about fixing the leak, or first of all diagnosing which part is actually causing the leak. i'm hoping there is a torn line connector seal or something easy like that...but i'm not holding my breath. my luck is that the TXV is bad and i'll have to remove the entire rear unit to replace it.

is there a commonly known failure mode at this joint location? if not, what are my steps to go about diagnosing which component failed?

 

The leak is actually between the expansion valve and the evaporator. It gets corroded and the corrosion causes the leak. You will need to replace the rear evaporator which comes with a new expansion valve on it. I also replace the seal on the bottom of the rear hvac housing. Clean off the extension tubes and install new o rings. It is actually pretty easy to remove. If you need removal instructions, pm me your email address.