Hi all,

hoping this post finds someone who was having primary switch issue with goodman furnace. (GMSS 921005 CNAA , GMSS921005CNAA)

I kept having 4 flashing lights, which indicates that there is an issue with primary limit switch. I replaced the switch, but the issue continued (it would run for about 4-5 minutes, shut off, fan would run, then repeat)

I finally tried removing the filter completely and it seemed to have fixed the issue. Thinking it was the filter, I put a new one in, and the issue started again. Then I just left the filter in but removed the T shaped metal-filter-remover thing and the issue was resolved. I realized that when I switched to cheaper air filter, it wasn't as sturdy as more expensive ones and it was causing poor air flow, because the fan was bending the cheaper air filter. Once the T bracket was removed, it was no longer impleading the air flow and the cheap air filter stayed straight.

It is going to be inconvenient to remove the filter but at least it works (I will have to use a pick to get the filter out). Now I can use very cheap filters and it should work just fine.

 

Welcome to the forums.

Safety switches are 99.9% reliable...... when they trip..... it's for a reason.
You have an airflow problem.
Make sure registers are open.
Make sure the return vents are clean and not covered.
If you have central air in that furnace..... you could have a dirty evaporator coil.
You should have the furnace checked and cleaned.