[noel1]

The truck is a 2002 7.3L Diesel Ford SD. 155,000 mi and serviced better than my wife but I digress.
My engine when it heats up, i.e. towing a load and running A/C in warm weather
Has a fan that is cycling up and down. This fan (my assumption) is the same fan that used to come on during the same above parameters but would achieve a higher RPM, run longer and then shut down until it was needed again. I assume a heat sensor exists somewhere.
The mechanic tested the A/C as well as replacing other parts in the engine cooling system to no avail. I have been told it can't be the turbo fan as it is small and runs all the time and I wouldn't be able to hear it. The main fan runs when the engine runs and doesn't cycle to my knowledge.
Is there a fan that these people don't know about that is sensor controlled. I'm not a mechanic so it seems simple to me that a sensor is malfunctioning as the fan seems to work just not as it did.