Before you have any repair done it would be worth while to have the guy that comes out inspect the heat exchanger for cracks/missing rings. Goodmans of that era had the older clamshell design and should qualify for a tradeup program if cracked/missing a ring. Better off getting a discounted tradeup than fixing the old one which may have a crack in it.
Its also much more likely to have a crack/ring problem if the thing was oversized and has airflow issues.
not a nube, an old and experienced..... plumber (not an hvac guy).
It ACTS like an airflow problem, but best as we can tell, nothing has changed with the airflow (notwithstanding a gradual clog in the A/C coil?) so we suspect a furnace problem.
More airflow (primarily in the return) fixes it, so does that mean the extra airflow is counteracting some clog, or the furnace has gradually (or suddenly) become more sensitive to limited airflow?
wish I knew. I like the idea of swapping the limit switch though
Swapping limits out is something that is only done by those who do not understand the values of proper troubleshooting. Randomly replacing parts is a hit or miss fix at best but most times misses the cause of the problem which then returns shortly after parts have been replaced.
This furnace needs to be properly diagnosed for temperatial differential, gas pressures and gas-air mixtures etc. Replacing parts on a furnace can make a small matter into a major problem quite effectively.
Why can we not pull out the a/c coil that we are not useing anyway. Did you not have a light that said the HI limit was tripped. That is a chep part unless being a plumper fixing frozen pipes is cheapper.