Rooftop furnace pressure switch?

[Plumber69]

I'm familiar with how residential furnaces pressure switches work. But rooftop units? Do they have a different style of pressure switch? How does it know the inducer is running

 

[Fitter30]

Its looking for a differential pressure just like any furnace. Some rooftops use a negitive pressure gas valve. Name plate should have the pressure listed or the install manual

 

[Sponsor]

 

[Plumber69]

Its looking for a differential pressure just like any furnace. Some rooftops use a negitive pressure gas valve. Name plate should have the pressure listed or the install manual

Its looking for a differential pressure just like any furnace. Some rooftops use a negitive pressure gas valve. Name plate should have the pressure listed or the install manual

I was referring to and air switch that the inducer activates. I found it... was built on to the inducer

 

[Fitter30]

Older units 15+ years had a centrifugal switch two wires when fan was running would make switch. Somethings they would dirty not make sprayed them with wd40.