Yup
If the burner lights should mean the blower vacuum operated switch is working, it shouldn't get as far as lighting in the start-up sequence if that switch isn't made. Of course, it can drop out after lighting and it will shut off the gas if it does. I am assuming your furnace does have a vacuum switch-- Small diameter rubber hoses going from the blower housing to a gizmo with wires connected to it. The vacuum switch usually controls a relay somewhere.
Yeah ... it does ... a couple of them in fact.
To left of the draft inducer and below the tube to the flue:
"New" (possibly unneeded) gas valve:
Two things you can check regarding the vacuum:
1) Turn on the furnace with a thermostat calling for heat. Just after the blower has started to run, jumper that vacuum switch. You may have to mess with trying different wires to find the right combination. I don't know if it is a normally open or a normally closed switch. There are specs for inches of water vacuum my furnace blower should develop, probably for yours too. That can be tested with a vacuum gauge if you know the spec with just the blower running, don't need the flame.
There are a number of wiring diagrams glued to the inside of the cabinetry ... I'll scope them out and see if I can find any specs, and see if I can discern the normal state (open/closed) and how they operate.
I've got several (automotive) vacuum gauges so I can check it ... but dunno if they are sensitive enough though ...
2) Make sure the air passages for the intake, air plenum around the burner, and exhaust flue are clear of any obstructions, not full of weed seeds and desiccated mice like my burner plenum box was. :laughing:
Right.
The top portion of the furnace (bonnet, plenum ?) that houses the AC evaporator is part of the original Bryant system's cabinetry. I've already noted that that it isn't correctly aligned with itself or the part of the Rheem f/a furnace below it that it connects to ... there is significant air leakage at one corner ... so I'll probably tear into that tomorrow, and see if I can't get it lined up and taped up better. Will scope out the evap housing for debris while I'm at it.
Will do the mice check as well.
The other main suspect is still the flame detector, what they call the "roll out" I believe. If the furnace shuts down after truly firing (you see a flame) for ~5-10 seconds, it can mean it senses no flame heat, so it shuts off the gas supply (in the gas valve) for safety.
I'm likin' that possibility too ... although the burner doesn't stay lit even that long ... three seconds tops.
For as cheap as it is ($10), you'd have thought that these dipnoids that are working on it, would have already just replaced it - to eliminate the possibility. At the very
worst, it wouldn't solve the problem and I'd have a spare flame sensor on hand ...
I do notice that the positioning of the sensor seems somewhat problematic (in that it is just barely in the flame) ... the bracket that holds it is clamped around a burner tube ... and of course with all the heating and cooling cycles it is rusted and seized and probably can't be repositioned without destroying it. Would like to find a pic showing the correct positioning from the factory but I dunno how successful I'll be at that.
I just have the feeling that something is not being satisfied in the start-up sequence because it never truly finishes start-up.
Yup ... my thoughts as well.
Couple of other data points:
1. There is a resettable breaker on the draft inducer housing (top center) ... this will occasionally trip and need to be reset ... but it's pretty rare in the big scheme of things.
2. The draft inducer
motor itself is pretty noisy ... seems like one of the bearings/bushings are going bad ... it's probably near, if not at, EOL. But it runs.
3. The flame of the second burner (of five) is pretty disturbed ... like there is (exterior) air blowing on it ... so maybe the heat exchanger is cracked again ... or something wasn't done correctly as far as sealing things up when they replaced the heat exchanger a couple of years ago.
I mentioned this last possibility to the (older) service guy and his immediate response was something along the lines of
"Oh no couldn't be ... that's just not possible ..."
Ahhh ... really ?
Seriously dude ... that's what ya wanna go with ?
Maybe ya wanna take a look at how they lined up and sealed the evap cabinet back to the furnace ...
The young dude that installed the (original) replacement gas valve managed to sneak off with the original. I didn't let him do that with the controller board when he replaced that, and I wouldn't have let him do it with the gas valve either ... if I had been paying closer attention at the time.
Older dude says
"No problem ... we'll get it off his truck" ... but he didn't bring it the last time he was here ... so he's going to get queried on that tomorrow ... before he comes out.
I really hate to say it - because I'm not inclined to do it typically - but these jokers may find out what disputed credit card charges are all about before this is all over.
