I have a 1997 or 98 Coleman Natural Gas Furnace with A/C. The blower works fine during the winter when I use heat. When I use the A/C, it seems that once the blower starts working for a bit on a hot day, it evetually (if on for more than 10 minutes at a time or so) starts kicking on and off while the A/C unit continues to run outside. When I turn the Blower to ON rather than AUTO, it's the same problem. If I keep the temp. up fairly high, the until only comes on once in a while and for only a few minutes, so it tends to run OK. Once I bring the temp down a couple degrees and it has to work harder, forget it. The blower starts cycling on and off. I got a brand-new A/C unit outside last summer. This intermittent blower issue started just before I got the new A/C unit. I thought the blower problem might go away after I got the new A/C unit, but no.

I was told there's a separate circuit board for the A/C vs the Heat side of the furnace. Could this be the problem? Any other ideas? Why would the fan work OK with heat, but become intermittent when using the A/C?

Does the motor feel really hot when it shuts off? If not it sounds like a faulty blower relay.

If it has a switch to change from heat to cool in the furnace, that is where I would start my diagnostics.