When I start my 1996 Volvo 850 GL (240K) even on cold mornings, the fan works and blows warm soon after. However after normal driving (about 40 miles), on restarts the motor does not blow strong (if at all), although I do detect the slightest bit of heat coming through the vents when the vehicle is moving. Also have been able to get the fan to blow properly with a medium to angry whack under the glove compartment on occasion. Winter's coming, heat is good in the wintertime. This summer I did pick up a donor blower motor/fancage from a (believe it or not) 1997 850 wagon with only 112K. So before I start disassembling things, any suggestions from the above symptoms as likely culprits other than the motor itself may simply be wearing out?

Thanks in advance.