My 4 yr old AC stopped cooling during the night. I called Air Express. Luckily Xavier, the owner, was already in the neighborhood on another job and came over ASAP. Checked the AC thoroughly and found that a small sealed canister of oil that is supposed to spin rapidly and disperse the oil (I really don't understand this stuff) The canister was leaking and the AC didn't cool. Xavier replace the canister and all is well.