I don't know if this has already been addressed but in case it hasn't here goes.
Do you have an air conditioner that is relatively new and just needed a new evaporator coil or is leaking refrigerant?
I just posted a reply on a thread regarding tenants complaining about repairs taking too long on an air conditioner and I realized that this A.C. issue needs it's own thread. There have been a number of class action suits (Thomas v. Lennox is the one I am familiar with) regarding failed coils. If you have just had to deal with a big repair bill on a fairly new A.C. unit, it might be due to this same defect.
I found this out completely by luck when I discovered our 4 year old Lennox A.C. unit was blowing hot air. I called the installer and they were 2 weeks out because temperatures here are in the 90s-100s right now. So I called another company and they said they could replace the coil for around $1,000. I freaked and started looking for new coils online and found out about this lawsuit.
Long story short, I was able to convince my original installer that I deserved a new coil and free installation because this was obviously a manufacturer's error (Lennox lost the suit) and I as a customer should not have to bear the cost of their mistake. It turns out that most of the copper coils used in A.C. units in the past 5 years or so are breaking down because of some reaction between the new R401 refrigerant and the copper coils. The coils need to be replaced with aluminum or copper that has been coated. Now for the disclaimer, I am not a lawyer or an HVAC technician. I am simply passing on information in the hope that it will help someone else on BP find out what I did much quicker.
I hope this helps at least one other person on BP avoid paying for replacing a defective coil in their A.C. unit.
Here is the website I found with the information
@Jeremy Gray This is great! Thank you for sharing!!