Any one have ideas on why when fan speed is increased the thermcouple shows a lower temperature reading. Can in duct can show temperature lower than ambient. I thought no but the folks ad Omega say it's possible due to colling effect!!!. Appreciate any references to this so called cooling effect. Thanks in advance.

At first sight what you are saying is not but If thermodynamic inversion takes place, then it is possible (check Joule-Thompson effect in your thermodynamics book) then check your geometry and where the thermocouple is located with respect to the velocity field, and plot the enthalpy field.