I am not familiar with the electrical as far as the AC is concerned, but I'm sure someone will chime in shortly.

You probably need to check your refrigerant charge with a set of good gauges & post the results here. A low charge will keep the fan from coming on.

There are 2 switches, one on the dryer & another near/at the thermostat housing that turns the fan(s) on & off. They are screw-in. One or both might be bad or have a connection problem.

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1987 300DT
2002 Ford F-250 7.3 Crew Cab Short Bed