Perform this Tuneup and see if it helps. Zero cost and when I've done it the results have been stunning. I did ours recently in connection with working on the blower motor (Coleman Mach series) and found the inside "fan" (a squirrel cage) was also very dirty. That work probably isn't essential, but the cleaning outlined by Chris Bryant in his blog thread is. Zero cost and not much labor. I ended up not replacing an older Mach that I thought was shot. Cleaned it and it went back to working like it should.