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In the repair manual somewhere there is a chart that shows when the fan is supposed to run. Just because the A/C compressor is on, the fan does not have to run. It only runs once the pressure in the A/C system has reached a threshold (or engine temp reaches ~206F for low speed, high speed is 220F?).

Does the A/C get cooler when you are driving down the road? that would show it is an issue with air through the condenser. If the A/C is not significantly cooler while driving down the road, you may just be low on refrigerant so it never comes up to pressure to turn on the fan. You say the compressor comes on...does it cycle on and off?

 

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Here you go. This is under engine control section, page 1009. If your refrigerant is not reaching pressure, the fan will not come on. Easy to check the pressure in the system to verify.

Also, under the A/C module of the manual there are extensive flow charts of what to check if your a/c is not cooling properly.

 

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If your friend can hook your truck up to a refrigerant machine to check pressures, see if you are meeting that 229psi threshold for the fan to come on while idling.

You have to remember you also have the mechanical fan there pulling air. If the mechanical fan is engaged, it may be pulling enough air through the condenser to keep the pressure low so the fan doesn't kick on. I was sitting in a drive through this weekend with the A/C on and the electric fan never kicked on.