THere is a grill next to the dome light near the rear view mirror. Air should be drawn through this grill any time the ignition is on. There is a fan that draws this air over a temperature sensor. Hold a piece of tissue paper to see if it is drawing air through the grill. If not, get a manual to find the location of the fan motor. On an 88 it is to the right of the glove box and accessible by removing the glove box liner.