Positive or Negative Pressure
 

Hi to engineer or controller out there that can help me with my question about the air switch above my hood range. What happened was i unplugged my air switch to install the new hood range but forgot to mark if i connect the air probe to positive or negative pressure of the unit.

This is link to manual http://www.emersonclimate.com/Docume.../0037-4898.pdf


From reading manual, i think i should connect to negative pressure but if it sits in front of blowing fan, should it be positive pressure. This hurts my brain

Thanks

My gut feeling is it should be negative pressure. If they designed it for positive pressure the chance of it getting plugged with contaminants your trying to exhaust would be too high. Even if they have it after the fan, if it is pointing down stream, it'll measure negative pressure, which is what I imagine it does. Either way it won't hurt anything if you screw it up. It'll either work or it won't :) If it doesn't, just switch it.

Probably positive. Do you know what the pressure switch is for? I assume it indicates a dirty filter and is installed between the fan and the filter on output of the fan meaning it will measure an increase in positive static pressure.

Hi CFM hoods required make up air through the furnace cold air inlet to prevent negative pressure in the house. Is the switch to the furnace fan?

thanks guys, I will check what the switch is for. It probably open some kind of air inlet somewhere that I need to find

Do you have the instructions for your range hood? Chances are if it came with the option for an air pressure switch, there should be some info in that literature. Unless it's a custom installation of course, or tied to another HVAC component in your house. In that case, you'd best get hold of the installer or qualified HVAC tech to determine what it does & how it should be wired.

Just connect the two wires of the switch and see what turns on.