The fan on my heater/ac is intermittent. It will work for several days, then will completely stop blowing at any fan speed. Occasionally I will hit a bump and it will start working again. Since it is intermittent, I think the motor is ok. What should I look at? Relay, switch? Something else?
A loose connection.
The next time the blower stops working, with fan speed set to high, reach under the passenger side of the dash, and with the handle of a screwdriver, rap on the blower motor.
If the blower starts working, replace the blower motor.
The problem could be with any of the devices in the circuit, including the motor itself. Using something like a screwdriver handle to tap on suspected trouble spots while the trouble is happening will most likely show up where the trouble is at.
Go for the fuse. Occasionally (I’ve seen it a few times) a fuse will fail with a hairline crack. It will look good, but sometimes not pass current.
It could be lots of other things (brushes worn out in motor, loose connection), but the fuse is easy to check and cheap to replace. Look in the owner’s guide to find out where it is.
The fans typically use two relays, one for high-speed and one for all the other speeds. Since you stated that the fan doesn’t work on any speeds, that rules out a relay as a point-of-failure.