Oh my goodness it is a hot one today; 93 degrees. Between stepping in dog poo, having ants crawling over me and my tools while cooking in sweat, UGH! Just as I thought there was an end to the day, another call comes up. This one was had a system freezing up. The homeowner suggested that it could be leaking Freon because of this. Since this was a call for the local utility; they had a service contract with same, they wouldn't cover a leak search or a recharge. I drove over and met the homeowner, a tall, thin and rather cheerful man in his sixties. He followed me as I went to the furnace, the coil, and the condensing unit outside. Both the furnace and the air-conditioner were thirty five years old, but the charge was perfect and I could see Freon in the sight glass (no fooling, many of these had sight glasses and this was a throwback to when air conditioning was set up like refrigeration back in the day). Not only that, the blower wheel and coil were clean top and bottom, the filter was new, and since the furnace had no secondary, this wasn't the issue either. I also noted that the blower motor was fairly new and the air flow was fine. All the registers and returns were open as well. So why was the coil freezing up?
Because this was an older furnace, it used a fan center instead of a control board, but this was also in perfect working order. Remembering that the thermostat activates the blower during a cooling call, I went up to investigate. Pulling off the cover, I smelled the electronics inside and got kind of a sickly sweet burning smell. This is not unlike the odor you get when a contactor, which is inside a condensing unit quits on the low voltage, 24 volt side. If your air is freezing up and you smell this inside your electronic thermostat, this is worth looking into. My suggestion is not to fix this yourself, as I get at least two or three calls a month where a homeowner botched a thermostat install. These can get expensive in a hurry, more so than if you just called me in the first place. Another thing to think about is most, but all thermostats sold in the home center are going to be less durable, less user friendly and likely will use AAA batteries, which is also a longevity issue in my experience. The one I removed was a AAA battery thermostat. Yes, the utility covered it. Maranatha!