I know the web is full of info on GM HVAC actuators, and I've been through a lot of info and get them in a basic sense. But I'm looking for some "deeper" technicals if anyone knows (including specific conditions that set B-code DTCs).
The back story is long, so I'll only relate the whole thing if anyone really wants to hear it! But it doesn't change the Q.
The vehicle is an '02 Envoy with the auto AC.
As I understand it the actuators rely on a position signal which basically comes from a potentiometer on one of those (crappy, cheap, plastic) gears inside of the actuator. I'm not worried about the specifics in that respect - but something like a 5V ref is sent in and the pot moderates to it range between - call it something like .5V telling the BCM all the way one way and 4.5V all the way the other way.
But let's say that something makes it so that the actuator only does half it's travel. (Maybe an obstruction in the vent work that, during calibration, "tricks" it into thinking it hit a limit or some weirdness with the gears). Theoretically, now the signal voltage only goes like 2.5V to 4.5V. In common-sense terms the BCM should "know" that's a problem - not the full range of travel - and set a code. But maybe it doesn't - that's just a human programming thing with people putting "if-then" statements into the software. Maybe they never though of that one. So I guess the short question is, if an actuator is working fine but can't do its full range, is the BCM programmed to "know" that?
(Ok. Short part of the long story - mode actuator that was throwing B3770. Only blows floor. This is the classic mode actuator failure - defaults to floor to favor proper defrost operation. Mode actuator replaced. B3770 gone, and blows face, but actuator literally only goes 1/2 way to floor so won't go full floor (so then I don't get full defrost when needed). But I've now got now codes. Should the BCM "know" that it's not going the full range? Or maybe I'm just waiting for the code... System recalibrated (by HVAC-B fuse pull) like 4 times. All else is normal).
The back story is long, so I'll only relate the whole thing if anyone really wants to hear it! But it doesn't change the Q.
The vehicle is an '02 Envoy with the auto AC.
As I understand it the actuators rely on a position signal which basically comes from a potentiometer on one of those (crappy, cheap, plastic) gears inside of the actuator. I'm not worried about the specifics in that respect - but something like a 5V ref is sent in and the pot moderates to it range between - call it something like .5V telling the BCM all the way one way and 4.5V all the way the other way.
But let's say that something makes it so that the actuator only does half it's travel. (Maybe an obstruction in the vent work that, during calibration, "tricks" it into thinking it hit a limit or some weirdness with the gears). Theoretically, now the signal voltage only goes like 2.5V to 4.5V. In common-sense terms the BCM should "know" that's a problem - not the full range of travel - and set a code. But maybe it doesn't - that's just a human programming thing with people putting "if-then" statements into the software. Maybe they never though of that one. So I guess the short question is, if an actuator is working fine but can't do its full range, is the BCM programmed to "know" that?
(Ok. Short part of the long story - mode actuator that was throwing B3770. Only blows floor. This is the classic mode actuator failure - defaults to floor to favor proper defrost operation. Mode actuator replaced. B3770 gone, and blows face, but actuator literally only goes 1/2 way to floor so won't go full floor (so then I don't get full defrost when needed). But I've now got now codes. Should the BCM "know" that it's not going the full range? Or maybe I'm just waiting for the code... System recalibrated (by HVAC-B fuse pull) like 4 times. All else is normal).