Your numbers and assumptions are correct.My furnace has recently developed never before seen problems, consistent with overly high output temperatures. I'm not yet sure whether my HVAC company considers them resolved. After I last spoke with them, I thought of a few questions that will help me to better understand the situation and what they've told me. Perhaps you could help me.
My 3-stage 355CAV-060's tag lists air temp rise as:
Low: 35-65 F
Med: 50-80 F
High: 35-65 F
If you wanted to arrive at appropriate output temp ranges, would you simply add return temp to those? IOW, if we assume a properly measured return temp of 70F, can we do this:
Low: 35+70 to 65+70 = 105F to 135F
Med: 50+70 to 80+70 = 120F to 150F
High: 35+70 to 65+70 = 105F to 135F
to project what the corresponding, properly measured supply temp ranges would be?
The tag also lists "Design Max Outlet air temp":
Low: 170F
Med: 170F
High: 170F
I haven't found a definition for that. Might this be the absolute maximize output temperature the equipment is designed to withstand, and therefore a temperature which basically should never be seen on the supply side during a heat rise measurement?
I haven't found information about the limit switch and the temperature at which it should open. Does anyone know where I would find that info, or might someone have it handy?
Thank you in advance, I'll followup up.