Okay, THAT sounds like it may be a cable adjustment problem. I'm pretty sure the 93's are set up with the slide control instead of the dial control like the newer models have. I have a '90 that had a similar problem in the past with the temp control. The control cable slipped and wasn't getting full cold. The function selector is set up the same as the temp control - here is the procedure for adjusting the control cable:
Control Cables
ADJUSTMENT
Function Selector and Temperature Selector Control Cable
To check the temperature cable adjustment, move the temperature control lever all the way to the left, then move it all the way to the right. At the extreme ends of lever travel, the door should be heard to firmly seat, indicated by a loud thumping sound, allowing either maximum or no air flow through the heater core.
To check the function cable adjustment, see that the function lever will reach the detents at the far left and right of its travel. In addition, check that the air flow is correct when the function lever is moved through each detent provided in the control assembly. If cable adjustment is needed, proceed as follows:
1. Disengage the glove compartment door by squeezing its sides together. Allow the door to hang free.
2. Working through the glove compartment opening, remove the cable jacket from the metal attaching clip on the top of the plenum by depressing the clip tab and pulling the cable out of the clip.
NOTE: The adjustable end should remain attached to the door cams.
3. To adjust the temperature control cable, set the temperature lever at COOL and hold. With the cable end attached to the temperature door cam, push gently on the cable jacket to seat the blend door. Push until resistance is felt. Reinstall the cable to the clip by pushing the cable jacket into the clip from the top until it snaps in.
4. To adjust the function control cable, set the function selector lever in the DEFROST detent and hold. With the cable end attached to the function cam, pull on the cam jacket until cam travel stops. Reinstall the cable to the clip by pushing the cable jacket into the clip from the top until it snaps in place.
5. Install the glove compartment.
6. Run the system blower on HIGH and actuate the levers, checking for proper adjustment.
Sorry, can't embed the diagram, but hope this helps.