On my 86, the heat strip is very weak, it is useful for breaking a slight chill or to supplement the furnace but won't really warm the trailer on its own. It is very hard to detect any difference from ambient airflow when it is on.
If it is working, you should have noticed a slight odor the first time it was turned on as accumulated dust was burned off the coils.
We use a little 1500
watt quartz heater and that does help a lot.
So, bottom line, even if your heat strip is working, don't expect much. I think you would be better off with something like I have rather than put a lot of effort into troubleshooting and fixing your unit.