Thorny problem of a very slow leak in our A/C refrigerant had showed up for the past several years, in the spring, when we activated the air conditioning for the first heat of the year. We would recharge the system then, and the A/C would work for the summer, but gradually--almost unnoticeably-- take longer to cool the house as the summer wore on. Thermo-Direct had run leak checks each year after I contracted with them for the biennial maintenance service. They discovered a faulty evaporator coil (installed by the (different) firm that installed the system in 2011, and replaced it under the equipment warranty. But the air conditioning failed the following year as well. Technicians this year ran a full diagnostic leak check by isolating the air handler, main refrigerant lines, and condenser and separately pressurizing the system to identify specific location of the leak. Leak was detected in the main refrigerant lines. That poses a potentially major problem because parts of those lines run through closed-in portions of the house walls. Here's where Derek came in--first of all, he remembered the system and its problems from previous visits to the house. Then, he (project manager) came out late in the day to examine the job, to make certain the technicians knew how to approach the job. Together, he and I figured out where the lines actually ran in our oddball contemporary-style house, and came up with a strategy that would minimize the damage to sheetrock (and minimized the likely follow-up repairs), and avoid running any surface lines to effect the repair. The next morning, he supervised the job on site, with a couple VERY capable technicians (Jake and Francisco), and they pinpointed the source of the slow leak on the first go (an inadequate joint-brazing by the original installers from two or more decades ago), repaired it, thoroughly checked the system, and installed an access panel at the site to allow easy access if needed at a later date. And, they included this in the long-term maintenance plan (well worth the dollars, after all is said and done) Outstanding sleuthing, prep, and supervision.Also want to give an extra shout-out to Jake, the lead technician for this repair. He's just flat-out skilled. And it seems they assign him the really challenging repair jobs because he's such a good problem solver. I joined them for the discussion of the problem when they all arrived in the morning--Derek, Jake, and Francisco--and saw them work together, with a lot of humor as well. The team obviously regards Jake as a go-to expert for difficult or challenging repairs, and he took his time to understand the job. Before they began the work on the main lines, he spotted a couple features that suggested where the slow leak was hiding ( Derek and I had not quite noticed these the night before). That prep work proved out--he did the initial exploratory cut in the garage ceiling, found the problematic brazing, and with Francisco, they made the positive ID and re-brazed the joint (that joint will never fail, even if we had an earthquake!) Concluded that the original joint was not adequately checked at full pressure, and, with the change in systems over the years and the higher pressure required by new refrigerant types, the joint failed when we installed a new system in 2011.So great job all the way around. And yeah, I know this is a lengthy review. But I have been very skeptical of HVAC firms, having had poor service, surly techs, and inadequate follow up with two other local firms, on system installation at two houses in Raleigh. Derek and the crew from Thermo-Direct have proven themselves competent, honest, and very responsive on every occasion.Derek, Jake, Francisco, as well as other techs Rotley and Jonathan, as well as the office staff (Landis and Alfonso) have all been great to work with.