Cleaning evap coil when cold outside

We have had the heat on for about a month or so. We had a few of warmer days and turned the ac on for those days. The last couple times when the ac came on we noticed a really strong dusty smell coming from the vents. We unfortunately are now noticing the smell with the heat on, although it’s not as strong. We are wanting to clean the evaporator coil. It’s in the attic. Is this ok to do? I understand we’d need to lightly rinse the cleaner even though it’s no rinse because we won’t be running the ac.

Is this ok to do? How much do we rinse it so? Thanks!