Limit Cycling Furnace
What is the limit of running cycling?
4 flashes indicate the path to the upper limit. Either you have over-the-counter software or your filter is full.
The upper limit device is a safety switch that shuts off the device if it is too difficult to stop the machine. There are two types of boundary changes. In both cases it is oval in shape, but has a small cap of 1. If it appears, you can reset it and the SW range will be reset. Other styles do exactly the same thing, but will automatically rearrange and don't need to rearrange after many trips and will need to be replaced.