Thanks, cb&q bob. Our locos do not have a/c in them (the a/c was removed to save on maintenance as it doesn't get that hot here, or so management thinks as they sit in their air-conditioned offices...), and so the climate control tab on the FIRE screen only has "vent" and "heat"--which is why I'm so interested in this fresh air make-up blower. If the climate control system (HVAC) is not turned on, does the fresh air blower still operate? I doubt it, as I don't feel any air coming out of the cab vents when the switch is on but the HVAC is off. Just checking, though. Last post here, I promise!