For reference to those Lennox Pulse furnaces still in use, I'll provide my experience. I bought my G14 80K furnace back in 1982, very early in the product life. Overall, it provided very reliable service until 2015 when I sold the house which was subsequently razed for a new structure. I had to have the furnace service only a few times over the years. My recollection is that early on the controller board was replaced with a newer model. I recall somewhat fondly the startup sound... much like a motorcycle, as well as the running thrum. One distinct DIY memory is that one winter, when over 30 years old, the furnace started to malfunction. You could clearly hear it start up, run for a few seconds, and then shut down again. It wasn't just misfiring, but was running and then stopping. I don't really recall how I diagnosed it, but, I do recall the actual problem and solution. The problem was in the flue gas discharge system, which I'll briefly describe. Combustion gases discharge into a 2" PVC Tee with the flue gas rising and discharging outside, and condensate dropping toward the bottom of the tee. There was a 1/2" pipe coming off the lower leg of the Tee draining condensate water in my case to a condensate pump. That 1/2" pipe, while appearing much like a Tee, actually is part of a trap that, inside the 2" lower leg, bent down into that lower leg. This trap keeps flue gas under pressure from blowing out the condensate line and into conditioned space, but allows condensate to drain when it gets above the discharge level of the 1/2" Tee. Now to my problem. Over the 30 plus years of service, some solids had collected in the bottom of the 2" Tee. Don't know the exact source of these solids, they might, for example have been dirt particles that came in through the combustion intake pipe. I doubt the could have been dirt in the gas, as that might have clogged the nozzle. Might also have been corrosion flaking off the inside of the combustion chamber and heat exchangers. What happened was that these solids built up at the bottom of the tee and were substantially blocking the flow of condensate water out through the 1/2" line. Instead, the condensate water was backing up in the Tee to the extent that the Pulse would stop firing. (It would shut down and then go through its restart process. Sometimes succeeding for a few seconds, sometimes not. Solution: I cut off the lower leg of the 2" tee, and drained out the trash at the bottom. I reconnected it with a 2" Fernco, and I was back in business. Truth be told, unaware of the internal 1/2" trap line, I cut through it when cutting the 2" pipe, so I reconnected it as well. (Glued). I was back on heat that night, and didn't have to wait for a service call.

I'm in need of a Carrier furnace manual 58MCA. Does anyone have one in a pdf?