Jim Katen

Not really. It's input is 150,000 btu/hr and its output is 124,500 btu/hr, which amounts to 83% efficiency (and is probably why it's called an 8300 turbo). The great majority of furnaces in the 1980s were 80% (or thereabouts) efficient and lots of them used draft inducers, as yours does. Several manufacturers were experimenting with much more efficient designs, which pretty much all sucked, by the way. Be thankful that you didn't have one of those. These old Aircos last a long time. Perhaps part of the problem . . . OK. Hold on here because this is really important for you to understand. The draft inducer fan should not, does not, *must* not "blow" the burner gases out through the flue. In an 83% furnace, those gasses are going to be in the 130 to 170 degree range and the furnace is expecting them to rise out via the flue as a result of their buoyancy. That means that after the flames are ignited, the pressure in the flue has to be less than the pressure in the heat exchanger. If it's not, the furnace won't vent properly and exhaust gases will enter the house. The whole point of the pressure switch is to monitor the pressure in the flue and shut down the flames if the pressure ever gets too high. (I suspect that it's looking for a difference of 0.5" wc.) The short cycling could be caused by the pressure switch, but if so, it's likely that the pressure switch is just doing what it's supposed to be doing and there's a problem with the natural draft of your flue. Describe it. How far does it run horizontally before it runs up vertically. What's the overall vertical height. Does it have a proper cap at the top. (These sometimes rust and fall down, obstructing the flue.) The short cycling could also be caused by the high temperature limit switch, (a failed heat exchanger could cause this) but when that happens, the cycles aren't usually that short - more on the order of minutes than seconds. Check your flue. Check your flue. Check your flue.

Please post a clear picture of the data plate; the silver sticker at the mid-left side of the picture of the furnace.

I only ask because the pressure switch has two tubes, which seems unusual if it's a regular furnace. The 2nd tube leads to what looks like a collector box that you'd find on a condensing furnace. I know that in the '80s manufacturers experimented with some odd configurations, so this might be one of those. Do you have a picture of the data plate, which would show the "category" of the furnace and several other technical details? Who suggested that the problem would be with the motor? (It's called a draft inducer, by the way.) The purpose of it is to draw a regulated amount of air over the burners and into the heat exchanger. After the flames ignite, the buoyancy of their hot air draws them up and out of the flue. The draft inducer has nothing to do with pushing the gases up and out of the flue. When the furnace is operating properly, the pressure inside the flue is less than the pressure outside the flue or in that collector box (or whatever it is) behind the draft inducer. If there's no negative pressure in the flue, the pressure switch senses this and shuts down the flame. Since that pressure switch has been changed and is still cutting out the flame, its reasonable to assume that it's just doing its job and that there might be a problem with the flue: an obstruction perhaps or some other condition that's preventing the buoyant gases from rushing up the flue. No. I was just wondering who wrote it and whether it's a spec for the switch or if it was a measurement of the actual pressure in the flue.

Is this a condensing furnace? If you remove the non-rubber-band hose and suck on it, does the furnace work properly? (It should - for as long as you can hold the suction.) If this is a replacement pressure switch, how did you choose it? Do its markings match those on the original switch? Who wrote 0.5" wc near the switch? This stands for 1/2" water column and might be a guide to choosing a new switch.

What Marc said. The pressure switch is trying to prove negative pressure in the flue. I'd start by looking for an obstruction in the flue and checking to be sure that the furnace room has an ample supply of combustion air. If those are both fine, then I'd test the pressure switch (or just replace it - they're cheap enough).

I'll bet the insurance company was thankful for your insight.

The International Association of Electrical Inspectors (iaei.org) offers training in solar and wind systems. I don't know anything about those classes, but I've found it to be a good organization in other regards.

I believe that the federal government requires the manufacturers to provide the label and the instructions that go with it. As far as I know, failing to obey the instructions is not a federal crime. If it is, it's not being enforced.

It might have been lost in the transformation from the old forum to this one. Lots of documents disappeared. Try https://www.building-center.org/williams-hvac-age/

Sorry, I didn't realize you were asking about the service neutral. My opinion: yes. It's a neutral whether it's grounded or not. It carries only the imbalance of the loads on the other two conductors.

It certainly won't be later. Might even by earlier. A Muffaletta from the Central Grocery beckons me. I'll let you know when my plans are solid.

Where is the house located? Solving problems like this can be very tricky, but it always comes down to lowering the humidity in the attic. A dehumidifier should not be necessary. Somewhere, somehow, relatively warm, moist air is getting into the attic.

It'll all work fine till the fuse holders loose their "spring" and you start to get heating at the connections, which causes the metal to get even more loose. The thing I love about equipment like that is the smell. There's always this great smell in those places.

Is the gouge in a glazed portion of ceramic? If so, I'd call someone who can apply epoxy that could be buffed to match the surrounding sheen. Unless you can match the color perfectly, I'd suggest a kintsugi-style repair in which you make no effort to hide the fact that it's a repair.

I'm planning to be there and I'd love to meet you.