Checking For Blocked Air Ducts
Our house is a two story 15 year old home with central air. The unit is in the basement. During the summer I shut off the register in the basement (there is only one) and about 1/4 of the registers on the first floor to force more cold air to be pumped into the second floor. During the winter I open them all up and there does not seem to be the problem. There are three air return ducts on the second floor. I think I might have a blocked air return duct. Here's my reasoning. I noticed that when the air conditioning turns on, the basement door would shut if it was open a little bit. We'd been in the house for 8 years before I noticed that. Now, add in the fact that I wallpapered one of the kid's rooms and left the grate covering the air return off for about a week (out of laziness, sad to say!). Putting two and two together, I'm wondering if a kid dropped a stuffed animal or something into the duct (the duct is accessible to them because there is a bunk bed next to it). I tried looking using a mirror and a flashlight with no luck. My thought is that if the system is being starved of return air it will suck it in from the basement and cause the suction that closes the basement door. Is there a good way to find an obstruction? Is there anything else that might cause the suction at the basement door? I change the filter on a regular basis (every other month or so), so I'm pretty sure it's not that the filter is plugged.
Answer:
We had a new outside AC unit installed a year ago and got a new A coil (I think that's the name of the heat exchanger inside the duct) at that time also. The problem existed before and after the new install. Also, the flow out the vents seems fine. Also, if it is a blockage on the exit, would that cause too much draw at the inlet? Again, the problem is that the system seems to be drawing it's air from the basement rather than the return ducts. On the subject of blocked air ducts: The living room of my house has floor registers to blow A/C; the ductwork is in the slab and is PVC, in most cases about a foot in diameter. There is one register that stopped blowing air a few months ago, and dirt and rodent droppings were found under the grate. I used a shop vac to suck out all the dirt that I could (it was visibly fully plugged with dirt and rocks), but apparently it is not completely cleared. The PVC for this duct is about 3 inches in diameter. My suspicion is that the rodent in question is a pocket gopher, as gopher activity has previously been seen just outside the window next to this register, and they like to block up the ends of their burrows with dirt. Unfortunately, I don't know the path of the duct, so I don't know if the point of entry is under the house or may be reachable from outside--my plan is to use an unbent clothes hanger to try to gauge the path of the duct, and if it goes straight towards the window far enough, attempt to dig outside to gain access and find the point of rodent breach.