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!
The best test for determining where the blockage is in an air system is a series of static pressure tests at critical locations thru your duct system. The tech will drill a small hole at various places in the system and take a pressure reading using a manometer.
This is an easy test to make and should not take long. It will determine exactly where the airflow restriction or restrictions are. It will prove if the problem is a restricted A coil or not.
Even though this is simple, few technicians know how to perform the test or understand it when they do it. You may have to quiz your contractor to see if they have a tech on staff who can do this and has the instrument necessary.
An NCI certified technician will be able to do the job easily.
try calling a contractor who specializes in test and ballance to do static presure test.
Thanks for the advice!
I actually aked the tech if there was "some sort of tool that could measure it" and he said its beyond their expertise, I would need more of an airflow/balancing tech. They are just the oil co, so they dont do the ductwork/balancing/pressure measurements. They are coming back to replace the fan limit switch (covered under our service contract, so he said its worth a shot), but he was doubtful that would fix the issue.
Ill contact another HVAC company Ive talked to to see if they have anyone that could come out and take pressure measurements and possibly re-balance the system (which Ive always wanted done anyway).
Another question (if anyone is reading ):
At this point Ive found 2 options:
1. Oil company still insists right way to go is coil cleaning.
2. I found another service co that would come out and check out the system. They will do a complete run through, but the cost of their troubleshooting will equal the cost of the coil cleaning itself (because I dont have a service contract with them).
Is the best option just letting someone else troubleshoot it and sucking up the cost, then paying for the fix on top of that? I know we cant use numbers here, but Im sure you guys realize we arent talking about miniscule amounts here. The cleaning cost might even come close to replacing the coil with a new one.