How do you determine if your Actuator, or heater temperature control, is bad. on 1996 Ford Crown Victoria

I have narrowed the problem down to either the heater temperature control or the actuator. How do you determine which is the problem. Can a bad temp control swtch, be determined by a specific means, or do I just change them both. HELP, three winters w/heat issues.

Asked by for the 1996 Ford Crown Victoria
i agree with goodguy, get a diag from someone with a scanner b4 guessing
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fords are bad for the heater box door breaking