This is a followup to my previous thread (about short-cycling).
Tech came out and figured low air flow. Pulled a panel off of the plenum to check out the A-coil, it *looked* clean. Turned on the fan and felt not much air getting past the A-coil. Used a rubber glove above the coil to demonstrate that not much air was getting by. Seemed to be more getting by the bottom of the "A", but towards the top (where the supply takeoffs are) didnt seem so much. However, air flow out of the supplies in the house doesnt seem low. He put a flashlight up to one side of the coil, and it was very hard to see any light on the other side.
My question - is the light shining test a valid one to determine if the coil is blocked? I viewed it myself, and the coil didnt have anything caked on it. Always changed the filters, etc. The furnace/coil was 2 years old when we moved in, 5 years ago. Ive done some work on the house that involved dust (the dreaded drywall dust) but I always left the HVAC system off during the bulk of the work, to avoid dust getting into the system.
He suggested a coil cleaning obviously, and made it clear its not an easy/cheap/quick job. Before I start agreeing that they do it, I wanted to be sure that its actually the issue. Also, judging that the airflow out of the supplies doesnt *seem* low, Im wondering if this problem may have existed since before we moved in? Cant figure out why all of a sudden it would start cutting off on high limit (unless its just a bad high limit switch? But that wouldnt explain low air flow thru the coil).
Thanks in advance!