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you have quite a few questions and some knowledge of what might be going wrong. Honestly, I would invest in a clamp meter. You can test without a clamp meter, but you would need a high amperage multimeter, I would not suggest this to a hobbiest. I would start with things like the filter first. Is it clean? new? any restrictions to the evaporator, (if a/c is installed, dirt build up ect). Are vents in some rooms closed restricting air? Is the blower cage itself clean or has build up on the fins maybe removed some of the capacity to remove air? If you have answers to all these questions and it does not solve the problem then I would suggest bringing out a tech. I don't like to have customers testing high voltage lines not knowing what to expect.
It's certainly ok to ask to get a refund, but honestly Paul, I think you need a tech. I'm not going to try to walk someone through testing high voltage circuits without some experience. I value life more than that. I Myself am very careful when testing high voltage.. It's not something I would put on a website!
I'm sorry, I hope you understand.
my guess is that it is Not a element, but more like a limit switch is opening. Air flow is a factor as well as constant metering of each of the element circuits. to do this with a multi meter is not the easiest or safest way to do so. I recommended a service tech to check. I think that does answer your original question.
As far as getting credit, I believe you would need to contact customer support. I'm not really sure as I am an expert on Hvac and haven't had anyone who needed to go that route. I wish you well... Hope you get the resolution you will be happy with...