Not a fuse. A dohicky (sorry for the technical name - lol) that, I believe, helps prevent interference with signals.

From what I see, the 126A has the 2 stage scroll and is a deluxe unit. Should be installed with a variable speed furnace or air handler. It has a full cabinet. Not on the current list so would be an older model. The 126B looks identical but has a single stage scroll. Being single stage it doesn't matter if on variable speed blower or not but only gets 14.5 SEER with standard motor and 16 SEER with the high efficiency motor like an Evolution furnace. The 116B is a Preferred. There's also a 116B which is a Legacy and wire grille like c-dave described. Used to be called the RNC series. So if you have a 126A without a variable speed indoor unit, better have a chat with the dealer. While it is a fancier unit than the B model, you don't get the benefits with a standard motor.

Hello, Make sure you have the right sized equipment. Using efficiency to calculate output of furnace is the first step. Don't let someone downsize you to the point of stupid. Yes new equipment is probably more efficient than your 50 year old furnace, but not necessarly. You can check the efficiency by dividing output by input and multiplying by 100. Many older systems were more efficient than people want to believe. Newer higher efficient equipment is smaller than older equipment, but the higher efficiency it is, the quicker it will fail. Heat exchangers are a common problem. As far as I know Heil is middle of the road good equipment. It is not popular in Texas, but never the less probably equal to most brands seen here. Installation of an AC system, usually requires larger ducts to cool the same sized romm as to heating the room. With this said, just admiring the existing duct, does not tell if it is large enough for the layman. Using rigid pipe is probably best with custom designed duct the top of the list. This just don't happen in Texas. Most homes are ducted with flex duct. It is cheap to install, and low labor. Air flow is quite with flex duct, but it has it's problems. If animals get into the attic, they can easily damage the duct looking for fun. I have some unwanted visitors in my attic. Since the duct is steel, the only damage was to the insulation last winter. I will reinsulate a couple of small areas and all will be good. Using round duct with insulation on the outside is a good comprimise for quality and durability. It cost about double of flew in material costs, and labor is probably triple, over using flex duct. Some areas of the country require metal duct. Just not Texas. if the unit is in a closet, it needs to be installed to local code. Proper exhaust venting and attic sealing. Fibre board is expected in some installations, but metal plenums are preferable. I recently saw a plenum make of 1/2 inch insulation foam board as found at Home Depot. I told the owner of the dangers of fire, but he was very cheap. This is not adequate and should not be used. Metal tape to seal joints at a minimum, and mastic joint sealer is prefered. If the registers whistle, they are either too small or the system is operating at too high air flow. If you use a variable speed blower you will never know you are screwed until the cooling does not keep up. IMO current practices are kinda overrated. I do not use nitrogen, I don't evac the system to 500 microns, but I also do not do 410. These practices are necessary with puron. Even then, the systems fail quicker than 22 systems. I have nitrogen, but do not see the need to purge with it. If I purge, I use 22 and recover it. I believe in filters.

A little voice wispered to me that the smoke when the motor went was a dual capacitor for blower and compressor. Another voice said in my other ear that he thought something shorted origionaly. I trust both so you should look closly at the cap for signs of burnt or swelled case. If that looks good,look around for a shorted wire or device. Still no joy? Have the compressor cap tested or just buy a new one and pick up a hard start while you are there. Right along here is where an HVAC tech will be required to get some hands on it unless you and/or your buddy feel bushey tailed enough to follow a step by step hand in hand with somone here or elsewhere.