hi.

i have a large exhaust fan which i control during the daytime using a temperature controller (the fan turns on and off at a setpoint)

at night time, i would like to switch the fan so that it is being controlled by a humidity controller instead of the temperature controller

both controllers are 120v ac. the fan is 120v as well and plugs right into controller

how can i use a relay so that the fan is wired to both controllers at the same time, but during the day/night only 1 of them sends power to the fan. i attached a drawing of what i'm trying to do hopefully it makes sense

thank you

 

You might be able to find a Timer-Module that has a "Double-Throw" Relay-Output,
that would simply and easily do the job.
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You could use a DPDT power relay (below):

 

If the fan is switched on by an increase in temperature during the day, and if it is switched on by an increase in humidity at night, then a simple solution would be to simply wire the two control switches in parallel.