Description of Issue - We have two central AC units in our home. One serves the basement, 1st floor, and a bathroom in the 2nd floor. The 2nd unit serves the remainder of the 2nd floor and the 3rd floor. That said, both units seem to run just fine for the most part, but after running for a while they both exhibit the same odd behavior. The blower fans under the coils will stop and then sound as if they're attempting to start up again only to stop, almost like bumping the motors with power and quickly disconnecting. They do this a few times and then eventually they will turn back on and start blowing air again. This does not happen every time the units call for cooling, but it happens quite often.
I have watched a lot of videos on what causes short cycling and cannot figure out why this is happening. Filters are clean upstream of blower, heat exchangers are clean on outside compressors. One of the blower motors is only a year old, one of the compressors is also a year old, and both blower capacitors are good. I've also checked the AC run capacitors on both outside compressors and they are both good.
I'm leaning towards a sizing or flow mismatch issue. I have thought about reducing the fan speed thinking maybe the blowers are too large. I intend on doing some quick calcs in the next week or so to see if there is a gross mismatch that sticks out (I am a mechanical engineer by trade but HVAC is not my specialty).
Anyone have any other ideas of things I can look to?
I have watched a lot of videos on what causes short cycling and cannot figure out why this is happening. Filters are clean upstream of blower, heat exchangers are clean on outside compressors. One of the blower motors is only a year old, one of the compressors is also a year old, and both blower capacitors are good. I've also checked the AC run capacitors on both outside compressors and they are both good.
I'm leaning towards a sizing or flow mismatch issue. I have thought about reducing the fan speed thinking maybe the blowers are too large. I intend on doing some quick calcs in the next week or so to see if there is a gross mismatch that sticks out (I am a mechanical engineer by trade but HVAC is not my specialty).
Anyone have any other ideas of things I can look to?
