Trane Gas Package Unit Won’t Ignite- HVAC

While performing fall/winter service I found this Trane unit not firing. Had a senior tech explain negative gas pressures. We found the problem and got unit up and running while doing the regular service.

[@realSamAndrew]

Why is it always negative? Is the inducer motor causing the negative pressure?

[@Davidandgoliathhvac]

Yes the inducer motor is essentially causing the negative pressure (-3 in this video) and once the gas enters (positive) it brings that negative pressure closer to 0 (-.22 in video). Also note this is for a commercial unit and not a residential gas furnace.