Furnace hot air flow

[alhnelson]

I had my Coleman furnace out several times this summer, working on the fan motor which I finally replaced, and everything seemed to work OK. Now that I have actually needed to use the furnace, I notice that the amount of hot air coming out of the floor ducts seems to be much lower than what I would expect or seem to remember. If I open the panel door and remove the furnace front panel, I get plenty of hot air blowing out. I also notice that with those doors closed, the furnace metal box seems to be hotter than it should be and cools off some when I open the doors. It seems that the blower is blowing plenty of hot air but it doesn't seem to circulate through the ducts as it should.

From what I can tell, the ducts should not be plugged. I do remember that when I put the motor/fan assembly back together, there was a metal bracket that went across the opening in the blower assembly, and it seemed like that could have gone back together in more than one way. I am wondering if by chance, I have installed that bracket the wrong way and it effects the air flow in some way. Does anyone have any experience with that assembly or any other ideas on the hot air flow? Thought I would run this by everyone before removing the furnace again.

Thanks much,
Al Nelson  #3401

[Robert P. Anderson]

I have had problems with other furnace squirlcage blowers.
It seams like they need sone backpressure to run at full speed. I would try and move the plate you said could possibly go on in a different  location. :roll:

[Andy Illes]

Hi Al,

Robert is right about some blowers needing backpressure, but since you say it works fine/better with the panel open, I agree with you that it sounds more like an obstruction in a duct.  Mine (not a Coleman though) had the same problem, which turned out to be due to hair from the previous owner's cats.  

There were wads inside both registers, and also one jamming the little flapper paddle that's supposed to swing up with airflow and activate a microswitch to only allow the burner to light if the fan's working.  That wad not only kept the paddle down, but also kept the switch open so the furnace seemed to work fine, except -  like yours - almost no air out of the registers.  Another thought... what about the return... is there a dirty filter?   Good luck, Andy

[alhnelson]

Thanks for the feedback. I think I have fixed the problem. I pulled the unit out again. There are no filters and the ducts seem to be clean. Inside the blower housing near the top is a metal U shaped bracket. The bracket can be mounted in one of 3 different positions, and it's two screw holes line up with screws in all of these positions. Unfortuneatly, I hadn't noted it's position the first time I took the unit apart so it was easy to put it back in a different position which seemed correct. In two of the positions, the depth of the bracket extends downward, reducing the air flow opening. In the third position, the depth extends back and the bracket forms more or less a duct across the top of the housing which has an opening the width of the housing and about 1" down.

With the unit removed, I hooked the blower up to a battery and experimented with the bracket in the different positions. I had started with one of the first two aforementioned positions. I found that the third duct type position increased the air flow (somewhat similar to a venturi effect). After continued testing in and out of the Clipper, I put it back together with the bracket position changed as noted. The airflow out of the floor ducts is noticeably improved and seems to be more like what I had remembered it to be before removing the furnace the first time. I still get a stronger flow of air coming directly out of the unit with the front panel removed but that is probably normal. Overall, it seems to be working normally.

Thanks again for your suggestions.

Al Nelson #3401