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A control system and method for operating a cooling fan in a coolant system of fuel cell power plant having a high temperature coolant loop and a low temperature coolant loop. The fan controller generates a fan control signal based on a first control signal from the high temperature coolant loop and

A control system and method for operating a cooling fan in a coolant system of fuel cell power plant having a high temperature coolant loop and a low temperature coolant loop. The fan controller generates a fan control signal based on a first control signal from the high temperature coolant loop and a second control signal from the low temperature coolant loop. The first control signal is a function of the waste heat energy in the high temperature coolant loop, and the second control signal is a function of the temperature in the low temperature coolant loop. The fan control signal may also be generated based on a third control signal which is a function of a localized ambient temperature such as the under hood temperature of a vehicle.

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1. A fan control system for a fuel cell cooling system of the type having a first coolant loop and a second coolant loop, the fan control system comprising: a first sensor generating a first input signal as a function of a coolant heat energy in a first coolant loop; a second sensor generating

1. A fan control system for a fuel cell cooling system of the type having a first coolant loop and a second coolant loop, the fan control system comprising: a first sensor generating a first input signal as a function of a coolant heat energy in a first coolant loop; a second sensor generating a second input signal as a function of a coolant temperature in a second coolant loop; and a controller including a first control circuit receiving said first input signal and generating a first control signal having a high state and a low state, a second control circuit receiving said second input signal and generating a second control signal having a high state and a low state, and a fan control circuit receiving said first and second control signals and generating a fan enable signal when at least one of said first and second control signals are in said high state, and generating a fan disable control signal when both said first and second control signals are in said low state. 2. The fan control system of claim 1 wherein said first control circuit provides a delay such that said first control signal has a high state when said first input signal is greater than a first predetermined value and said first control signal has a low state when said first input signal is less than a second predetermined value, said second predetermined value being less than said first predetermined value.3. The fan control system of claim 1 wherein said first sensor generates said first input signal as a function of a position of a diverter valve controlling coolant flow through said first coolant loop.4. The fan control system of claim 3 wherein said first control circuit provides a delay such that said first control signal has a high state when said position of said diverter valve is greater than a first predetermined value and said first control signal has a low state when said position of said diverter valve is less than a second predetermined value, said second predetermined value being less than said first predetermined value.5. The fan control system of claim 1 wherein said second control circuit provides a delay such that said second control signal has a high state when said coolant temperature is greater than a first predetermined value and said second control signal has a low state when said coolant temperature is less than a second predetermined value, said second predetermined value being less than said first predetermined value.6. The fan control system of claim 1 further comprising a third sensor generating a third input signal as a function of a localized ambient temperature, said controller including a third control circuit receiving said third input signal and generating a third control signal having a high state and a low state, said fan control circuit receiving said first, second and third control signals and generating a fan enable signal when at least one of said first, second and third control signals are in said high state, and generating a fan disable control signal when all of said first, second and third control signals are in said low state.7. The fan control system of claim 6 wherein said localized ambient temperature is a maximum of a plurality of localized ambient temperatures.8. The fan control system of claim 6 wherein said third control circuit provides a delay such that said third control signal has a high state when said localized ambient temperature is greater than a first predetermined value and said third control signal has a low state when said localized ambient temperature is less than a second predetermined value, said second predetermined value being less than said first predetermined value.9. A cooling system for a fuel cell power plant comprising: a radiator having a first radiator section in fluid communication with a first coolant loop and a second radiator section in fluid communication with a second coolant loop and a fan disposed adjacent said radiator and operable to pass air through said first a nd second radiator sections; and a fan control system including: a first sensor generating a first input signal as a function of a coolant heat energy in a first coolant loop; a second sensor generating a second input signal as a function of a coolant temperature in a second coolant loop; and a controller including a first control circuit receiving said first input signal and generating a first control signal having a high state and a low state, a second control circuit receiving said second input signal and generating a second control signal having a high state and a low state, and a fan control circuit receiving said first and second control signals and generating a fan enable signal to turn said fan on when at least one of said first and second control signals are in said high state, and generating a fan disable control signal to turn said fan off when both said first and second control signals are in said low state. 10. The cooling system of claim 9 wherein said first control circuit provides a delay such that said first control signal has a high state when said first input signal is greater than a first predetermined value and said first control signal has a low state when said first input signal is less than a second predetermined value, said second predetermined value being less than said first predetermined value.11. The cooling system of claim 9 wherein said first coolant loop includes a diverter valve controlling coolant flow through said first coolant loop and said first sensor generates said first input signal as a function of a diverter valve position.12. The cooling system of claim 11 wherein said first control circuit provides a delay such that said first control signal has a high state when said diverter valve position is greater than a first predetermined value and said first control signal has a low state when said diverter valve position is less than a second predetermined value, said second predetermined value being less than said first predetermined value.13. The cooling system of claim 9 wherein said second control circuit provides a delay such that said second control signal has a high state when said coolant temperature is greater than a first predetermined value and said second control signal has a low state when said coolant temperature is less than a second predetermined value, said second predetermined value being less than said first predetermined value.14. The cooling system of claim 9 further comprising a third sensor generating a third input signal as a function of a localized ambient temperature, said controller including a third control circuit receiving said third input signal and generating a third control signal having a high state and a low state, said fan control circuit receiving said first, second and third control signals and generating a fan enable signal to turn said fan on when at least one of said first, second and third control signals are in said high state, and generating a fan disable control signal to turn said fan off when all of said first, second and third control signals are in said low state.15. The cooling system of claim 14 wherein said localized ambient temperature is a maximum of a plurality of localized ambient temperatures.16. The cooling system of claim 14 wherein said third control circuit provides a delay such that said third control signal has a high state when said localized ambient temperature is greater than a first predetermined value and said third control signal has a low state when said localized ambient temperature is less than a second predetermined value, said second predetermined value being less than said first predetermined value.17. A method for controlling a fan in a cooling system of a fuel cell power plant, the method comprising: determining a heat energy of a coolant in a first coolant loop; determining a coolant temperature of a coolant in a second coolant loop; generating a first control signal having a high state when sa id heat energy is above a predetermined level and a low state when said heat energy is below said predetermined level; generating a second control signal having a high state when said coolant temperature is above a predetermined temperature and a low state when said coolant temperature is below said predetermined temperature; enabling a fan when at least one of said first and second control signals are in said high state; and disabling said fan when both said first and second control signals are in said low state. 18. The method of claim 17 wherein the step of generating a first control signal further comprises generating a first control signal having a high state when said heat energy is above a first predetermined level and a low state when said heat energy is below a second predetermined level, said second predetermined level being less than said first predetermined level.19. The method of claim 17 wherein the step of determining a heat energy of a coolant in a first coolant loop comprises identifying a diverter valve position of a diverter valve in said first coolant loop to selectively direct coolant to said first radiator section.20. The method of claim 19 wherein the step of generating a first control signal further comprises generating a first control signal having a high state when said diverter valve position is greater than a first predetermined position and a low state when said diverter valve position is less than a second predetermined position, said second predetermined level being less than said first predetermined level.21. The method of claim 17 wherein the step of generating a second control signal further comprises generating a second control signal having a high state when said coolant temperature is above a first predetermined temperature and a low state when said coolant temperature is below a second predetermined temperature, said second predetermined temperature being less than said first predetermined temperature.22. The method of claim 17 further comprising the steps of: determining a localized ambient temperature; generating a third control signal having a high state when said localized ambient temperature is above a predetermined temperature and a low state when said localized ambient temperature is below said predetermined temperature; enabling a fan when at least one of said first, second and third control signals are in said high state; and disabling said fan when all of said first, second and third control signals are in said low state. 23. The method of claim 22 wherein the step of determining a localized ambient temperature includes determining a plurality of localized ambient temperatures and determining a maximum localized ambient temperature for such plurality of localized ambient temperatures.24. The method of claim 22 wherein the step of generating a third control signal further comprises generating said third control signal having a high state when said localized ambient temperature is above a first predetermined temperature and a low state when said localized ambient temperature is below a second predetermined temperature, said second predetermined temperature being less than said first predetermined temperature.