97 Accord EX blower motor intermittent

My daughter's car. She states that the blower motor fails to come on when she turns the fan speed control knob, but, it will then come on later while she is still driving the car. She states that the control knob does not feel loose. Looking for a blown fuse would not be feasible, I think, as the fan does come on eventually. This problem first started in the summer(July/August?), and was very rare.Lately, it has happened more and more frequently. Today, she states that the blower worked fine on the way to work, but failed to come on at all, even though she made several stops at several stores on the way home. Any ideas?
Thanks. Vic.

Does jiggling the blower knob make any difference?

No. That's what I meant by the knob not feeling loose. I thought that perhaps the control was stopping somewhere near or between what I imagine are contact points, and that subsequent bouncing along the road would finally make contact, and the fan would come on.
It may be useful to know that her airconditioner underwent an extensive repair during the summer. It has been my experience that a malfunction can usually be traced to what was touched last. Still, that doesn't explain why the fan failed to come on just once during the summer, and has just recently started failing more and more frequently.
Thank you for your kind attention. I'd appreciate any and all hints, including what sort of shop she'd take it to.
Vic

The current for the blower motor is high, so there is a heater motor relay that activates when the key is tuned on. When it is activated, voltage comes from the battery to a 30 amp fuse, through the relay to the blower motor to the switch and then to ground. (If the fan switch is any position other then full speed or off, it goes through a series of resistors to control speed.) So things that may cause your problem include the blower motor, the fan switch, the heater motor relay or power to the heater motor relay. The easiest way to troubleshoot is if the thing doesn't work at all.

I was actually working on this same problem yesterday on my 94EX. In my case the blower motor was just wearing out, as electric motors tend to do over time. I took mine out and, with it plugged in, turn it with my hand while the switch was on and it started working again...this is a temporary fix of course but it had just stopped on a dead spot in the motor. You can get one for about $60 at any autoparts store and it's easy to change, just buy a haynes manual for $8 while your there and it will tell you how to do it. It's not so hard that's it's worth paying $75 an hour for labor to fix it. You should be able to do it in about 30min or so. Good luck.

the manual will also tell you how to test the motor so you know that it is in fact the problem

Thanks for the input. I appreciate it. I'm at a disadvantage in that although my daughter lives just 15 miles away, we both work, and the only trouble shooting I can do for now is via telephone. I had her crank the car while still in the garage, and had her turn the AC on. The green light in the AC button came on, and she reports that the engine rpm and sound changed, which indicates to me that the compressor is kicking in. However, there seems to be no circumstance under which she can make the fan blow. We're near Atlanta(Gwinnett county), and the weather has turned cold. Thank God for flowthrough ventilation.

One final note. She took the car to a shop near her work. They replaced the blower motor to the tune of $284!. That's the price of being a single young female. Thanks again to one and all for your helpfulness and generosity.
Vic