What is the coolant valve next to the rear L bracket for?

Does it have to be positioned perfect? Cause I broke the mounting bolt for it and don't know if I should just put it back on.

 

forgot.... 93 CX hatch. It should be on every 92-95 Civic but someone gonna ask what car I have.

 

Thats the cabin heater temp control valvle ( I guess from your description). It controls coolant going to the heater core. If its not affixed to the firewall you might malfunction the temperature slider. I had to remove mines when I put in motor mount inserts.

 

thanks...

I decided to pull it off when I put the rear bracket on.