I have a 2004 Ford F150 and when the weather warms up the power steering stops working?

When the weather is cold the power steering works fine but when the weather starts to warm up the power steering stops working

Added (1). the belt looks fine but if the pump was bad then why is power steering working just fine in the winter time

It might be the belt is worn out, check for belt tension or replace it, if it continues I guess next step replace the power steering pump