The fan speed selector switch control only works on the highest speed. When I put the switch to the lower speeds there is no air, and I can't hear the motor working. It's as if it is off in the lower fan speeds. It's winter and I would hate for it to go out completely, Any ideas what might cause this, or how to fix it?

Sounds like a bad blower motor resistor.

Most likely the plug going into the speed resister is overheated and damaged. Please inspect the terminals on both sides. If the resister ends up being ok then take a look at the speed control switch. Please write back with any questions.

Hi, the resistor is screwed to the side of the blower housing behind the glove box. See procedure below to replace the resistor. You don't have to complete all steps in the procedure. just work your way to the point that you can unscrew the resistor. Please let me know if you have questions, and thanks for using FixYa.

1990-93 Accord

See Figures 2, 3 and 4

1. Disconnect the negative battery cable. If so equipped, disable the Supplemental Restraint System (SRS).
2. Remove the glove box.
3. Remove the glove box frame (lower support)

Fig. Fig. 2: Remove the glove box and frame

1. If not equipped with air conditioning:
   1. Remove the three screws and remove the heater duct.
   2. Remove the blower mounting nuts. Unplug the wiring from the blower motor, resistor and recirculation control motor, then remove the blower assembly.
   
   
2. If equipped with air conditioning:
   1. Lift the carpet in the passenger compartment. Remove the side cover (kick panel).
   2. Remove the control unit bracket nuts; unplug the five connectors and remove the control unit bracket.
   3. Remove the retaining band, then remove the blower lower covers. Do not break the tabs on the lower covers.
   4. Remove the retaining nuts and remove the blower assembly.

Fig. Fig. 3: Air conditioned models require the removal of the control unit. Handle it carefully

Its the relay for the motor. When the relays go the high speeds will operate but the low speeds will not. Should not be too expensive and is easy to replace, only hard part is that sometimes they put them in places that are hard to acess.

Sounds like you have either a bad fan connection or you need to replace the fan motor itself.

Check all the wiring leading to the fan, and the fan controller.

Btw, I’m available to help over the phone in case u need at https://www.6ya.com/expert/sean_54c3a3dc48a7773c

Usually when the blower fan only operates on hi speed, its because of a failed blower motor resistor. You still have hi speed because on hi, the power going to the blower motor goes directly to it, as opposed to the lower speeds, when the power is routed through the resistor, thus lowering the voltage, which in turn lowers the speed of the fan. The resistor is usually located near the blower motor itself, under the hood back near the firewall.

the various speeds are controlled through resisters (spring-like in apperance) one of different value for each speed, none for highest speed as the power gets to the blower uninpeeded . the resistor pack should be located on the center of the firewall, held by 2 screws. thats under the hood. where the engine bay ends....

replace switch, works 9 times out of 9.

This is a typical  symptom of a failed blower resistor. These have multiple taps for the different speeds but the highest speed just bypasses the resistor completely; that is why it still runs full-tilt.
That resistor may or may not be inside the passenger compartment and could be accessible from under the hood, probably mounted on the firewall or under plastic hoods covering part of the heater/AC exchangers.
I'd recommend buying a Haynes or Chilton manual for your car that should cover the location of that part and perhaps give you information on how to best access it. The books are $17-$30 US and available on line or at any auto parts store and will earn their keep pretty quickly.    

Call your local GMC Dealer and see if they have the climate control panel in stock. What happens is the circuit board on the back of the panel shorts out. The panel comes as an assembly and is very easy to replace. Don't go with a wrecking yard piece. I made that mistake once and it didn't work either. I got one from the Chevy dealer and it worked perfectly.