Hi, I have a 58 MVC in the crawl space which has a filter box between the furnace and the return ducts. I pulled out the filter to check it and happened to notice that I could see into the blower chamber in the furnace. I saw a couple of things of concern.
First, there was a circular hole about an inch wide in the bottom of the blower chamber where wires were coming in (presumably to the blower fan). There is no seal around the hole or wires, so I imagine air from the crawl space is being pulled in to the blower chamber (post filter) and distributed through the home.
Second, upon close inspection, the door to the furnace was not on completely right and there was a few small spaces which would allow crawlspace air to be sucked in as well. In the dark, I was able to stick a flashlight through the filter box opening and shine light through the blower chamber---I could see the light coming through small spaces between the furnace door and the furnace where it did not seal, so certainly air could pass through as well.
I'm no expert, but I thought a blower chamber in a furnace would be sealed very tightly. Also, I'm surprised the furnace door is "the seal" between the blower chamber and the outside. In my upstairs furnace (different model), you can take off the furnace door but still do not have access to the blower chamber.
Does this seem right? Any thoughts on what should be done? Thanks very much in advance.