Lennox Don't Work In The Cold

how bad is the shipping turnaround for the sensor.

I had to replace the fan motor on my seriously old GE 105k input btu / 85 btu bonnet gas forced air antique two weeks ago when ambient was below freezing. I was able to find one locally where I'd done business before. Probably 15 years ago, on a super heavy duty box fan motor that chugs all summer in the attic window venting the whole house nicely as long as I open and or close the right openings per time of day. We do have a few ceiling fans and 2 window A/Cs for the 2 or 3 weeks a year that they are necessary.

I had a replacement fan limit switch for the furnace I should have replaced 2 years ago, but I was able to make the old broken limit switch work before I had the replacement in hand and just never bothered. I had a replacement run cap I ordered at the same time as the fan limit switch, but the tech at the motor distributor tested both caps and they both tested good accordingly. This time I replaced the fan motor the fan motor, run cap and the fan limit switch. And the weird 60Hz buzz from the new motor only lasted a couple of days.
Now I need to go into the fan control box and label all the wire, transformer, and solenoid connections and get OEM part numbers so I'm prepared for next time.

 

I had a similar problem with a Ford tempo. Radiator fan would not come on. I hooked up a manual switch to initiate the circuit. Perhaps running a switch to the inside of the house would be a temporary fix?

 

There was a bulletin like that in 2009 for Unitary Products Group brands (Coleman, Luxaire, York), YS00209:

If the electrical contacts within the
pressure switch body become contaminated with a foreign material, the switch may close
mechanically but may not close electrically at the calibrated set point, causing the control
to detect a pressure switch that is open when it should be closed. This will result in a 3flash
error code, and the furnace control will not continue the ignition sequence.
To address this problem, the switch supplier has made a recent change to the switch
construction to add an industrial contact lubricant that prevents contamination from
adhering to the electrical contact surfaces. Testing has shown that this makes the contacts
many times more resistant to contamination by foreign substances. Pressure switches
with code dates of 0309 (third week of 2009) will have this new construction.
...
The contamination on the
contacts is usually silicone carbide, the source of which is the silicone hose connected to
the switch. Silicone molecules outgas from the hose and migrate to the switch contacts,
eventually affecting the electrical connection.
​

Maybe something similar with the Lennox, though as far as I know that isn't a UPG brand?

I had a colleague at $work whose furnace once had a similar pressure switch issue. He made a temporary jumper with a toggle switch in it so he could get through the start-up protocol conveniently: ramp up (flip switch), ramp down (flip again), ramp up (flip again), good to go until the next cycle.

My furnace picked last week to act up. Considerate of it, since last week was much warmer (but I knew this week was coming).

I noticed on Wednesday night it was making, repeatedly, all the sounds it always makes leading up to ignition, but never the sound *of* ignition.

It even made the click of the gas valve. But no ignition. So my first thought was "did somebody shut the meter off?" But a quick check of the kitchen range proved the gas was on. So something had happened in the gas valve, where even after the loud click of the solenoid there wasn't gas to the burners.

Was my gas piping to the furnace somehow restricted? A manometer on the valve's inlet test port showed a healthy 7 or so inches of water incoming gas pressure. And it didn't drop when the valve clicked. But the water in the manometer did make a tiny bounce when the valve clicked. So the click was making something happen. A little bit of gas went somewhere.

Manometer on the outlet test port showed no discernible pressure when the valve clicked.

This was a valve that had been an irritating black box to me ever since I put the furnace in 12 years ago. It has a five-pin electrical connector:

One is ground, one is power to the valve's electronics, one drives its big on/off solenoid. The other two are labeled RXD and TXD, and are clearly how the modulating-furnace control board communicates with it to say what gas pressure is wanted. But using what kind of communication, and then what does the valve do to change the pressure? All of that was undisclosed black-boxism in the original literature that came with the furnace.

One nice thing about a dozen years passing is that, by now, literature can be searched up online that explains the darned valve.



It's sort of a cousin of a Prius EGR valve!

The Prius valve is much simpler, and its stepper motor rotates on a threaded shaft that directly moves the main valve pintle in and out.

In this valve, the stepper motor rotates a threaded shaft moving an adjustment nut (that can't turn) up and down, changing the spring pressure on the smaller pilot regulator diaphragm. The gas pressure in that pilot circuit then acts on the main diaphragm to push the main valve open.

So clearly, I had a main valve not opening, because the pilot circuit wasn't developing its pressure for some reason. When the solenoid valve opened, gas flowed into the pilot circuit (hence the visible bounce in the inlet manometer), but was passing freely by the pilot diaphragm and escaping into the valve outlet (where the pilot flow by itself is too tiny to count).

But why? Was the stepper motor not stepping? Was that spring broken? Was there some debris under the pilot diaphragm?

So that was when I went to the local parts house where I always used to go to buy such things (because who wants to wait for shipping when the furnace doesn't work in December?), and they don't stock it. They quoted me around $470 to have it the next day. The guy flat-out told me I could probably do better online.

So I looked online and found the exact part (from the furnace's 12-year-old parts list) around $300 at supplyhouse.com and they could also have it to me the next day. But there's also an identical-looking valve with identical specs (as far as specs were shown), where the part number ends in -554 instead of -508, that seems to be newer, and only $190. But I never found anything online that listed either valve as substitutable for the other.

So then I thought, do I gamble $190 on that valve, where if it turns out incompatible then I have to spend the $300 anyway and wait for another round of shipping?

In the end I took the gamble, and when the -554 valve arrived, it did clearly say, on the box, "service replacement for" and a bunch of numbers including my original.

But while I was waiting for delivery, I took the old one apart. I went in thinking only to get it apart and satisfy my own curiosity, but as it came apart cleanly and the rubber gaskets survived, I started to think I might even be able to put it back together too.

I was expecting to find something obvious like a busted spring or damaged pilot diaphragm. What was weird was that I did not see even one thing that looked like a smoking gun.

The "adjustment nut" was in the fully-retracted (lowest pressure) "home" position, all the way up against the stepper motor. It was pretty tightly up there. Not wrench-tight by any means, but more finger-tight than I expected; after all, it's only the torque of the stepper motor that gets it there.

Just like the Prius EGR valve, there's no sensor for the position. They just use the old stepper-motor trick of starting off by sending some impossible number of steps in the "home" direction, knowing it will go there and not be able to go farther, and the rest of those steps will be wasted, and then its position is known and steps in the "open" direction can be counted from there.

But the Prius EGR valve has an actual hard stop built in, where the rotor gets back to a home position and stops cold (as long as the stop isn't mashed), so it won't get wound up tight on the threads.



This gas valve has no stop like that. It just finds its home by spinning the stepper motor homeward until it can't go any farther because the nut got tight on the threads.

Still, if the stepper motor had enough torque to get into that situation, it should have enough to get back out, right?

Maybe not if it sat there in homed condition for a long time. This more recent literature for the valve has a warning about that:



I think my furnace's firmware was written before the valve guys added that note. If the furnace has been power cycled, a first thing it does on power up is send the valve home, and won't send any move command until the next call for heat. If we had a power outage in early summer (we did), the valve could have been sitting there tightened up at "home" all summer and most of the fall.

So I put a little Sharpie mark on the back end of the stepper motor shaft, and put the valve back together without the plastic trim piece, and made a call for heat, and sure enough the motor made a few seconds of "I'm trying to step" noises and the Sharpie mark never budged. Eureka!

So off came the stepper motor and I loosened the adjustment nut a few turns and reassembled that way. Sure enough, as soon as the furnace powered up, the shaft spun a few turns in the home direction, and stopped there, then during the ignition sequence it spun 3½ turns in the pressure-increase direction, and the igniter glowed, and I smiled and waited for the click and the welcome whoosh of flames.

Click.

No whoosh. WTH? I'd already found the smoking gun and fixed it!

So I took the stepper motor off again, and grabbed a drywall screw with a head the right size to fit in the adjustment-nut channel and push on the spring. Left the motor and nut just hanging in space by its wires, and mouthed the words "hold my beer and watch this", and made a call for heat.

The motor, hanging in space, spun freely in the home direction, then stopped, then went 3½ turns the other way, and I pressed on the drywall screw with what I guessed to be about 3½ turns worth of pressure, and waited for the click.

Click. No whoosh.

The control board allows a few seconds to detect flame before it gives up, so I just started pressing the drywall screw harder. And eventually I hear, and feel through the screw, a little "poit!" from the rubber diaphragm.

Whoosh! Yay flames!

So there I am making tiny motions of my thumb on the drywall screw to get loud flames, quiet flames, middlin' flames. The furnace board normally runs at around 70% for a half minute or so then throttles back, so I watch for the stepper motor to back off a couple turns, and I ease up a similar amount on my thumb, and there we are at low fire. And then I put the whole thing back together and ran several test cycles in low, mid, and high fire modes and everything was a-ok.

So here's what I think happened: a cascade of two things. First, there was that power outage way back in the cooling season, leaving the valve "homed" for so long that the motor and nut got stuck that way. But then, the first time heat was called for and the motor couldn't move, there was so little spring pressure on the pilot diaphragm that when the solenoid valve opened, the gas pressure pushed the diaphragm up—poit!—into a domed-up shape where it wasn't closing off the pilot passage at all. And then, even when I unstuck the motor and nut, the normal spring pressure just wasn't enough to poit! the diaphragm back down into the right shape. That only happened when I pushed the spring a little harder by hand. And then it was fine.

I did swap in the new valve when it was delivered, because I'm guessing my Authority Having Jurisdiction wouldn't be thrilled about running with a hand-repaired gas valve. But I did run a nice long cycle before bedtime, staying right by the furnace to watch it, to get the house temperature up, then turned the furnace off overnight, and I repeated that in the morning, just to keep the house tolerably warm before I had the new valve installed by the next night. And I have saved the repaired valve where I'll be able to lay hands on it if a similar future situation comes along and I need a stopgap while waiting for a replacement.

Amusingly, once I reassembled and readjusted the repaired valve, its outlet pressures at high and low fire were more spot-on than I had ever been able to get them when it was new. The way you adjust it was always annoyingly black-boxy: you aren't turning any actual mechanical thing, you're turning a rotary single-hexdigit switch, sixteen positions 0–9, A–F on the valve's circuit board. It comes in the box set around 7 or 8, and if the pressure on your manometer is too high, you can click it down toward lower digits, or too low you can click it toward higher. Nothing stops the switch wrapping right around between 0 and F, so if you're not watching while clicking you can click right from the lowest pressure to the highest or vice versa. And this one switch controls both the low-fire and high-fire adjustment, making it really difficult to get them both quite right. At installation, I had had to settle for about right on top, and pretty close on the bottom. But after the home surgery, I could get both ends closer than they'd ever been.

They changed that adjustment scheme in this newer, -554 valve. There's still just the one hexdigit rotary switch. But now you really can't tell anything from where the switch points, 0–9, A–F. The valve's firmware only notices when you change it, notices which direction you went, and increases or decreases a 64-step adjustment it remembers in a hidden nonvolatile memory. Now nothing special or different happens when you click between 0 and F, the internal value keeps going up or down depending on which direction you clicked.

And the new valve has two of those values hidden internally, one for the high-fire end of the range and one for the low. You still have only the one hexdigit switch to turn, but if the valve's current position is 68% or above, when you turn it you're adjusting the high end, while if the valve's current position is 35% to 67%, you're adjusting the low end.

Happily, that's explained in the valve's literature that can be found online. Once you grok it, it is easy to get both the low and high fire pressures just right. But it would drive you stark staring bonkers if you were looking at the old instructions and expecting it to work that way. So I wound up the whole project sitting at my desk going through the original manuals putting sticky notes on all the mentions of how the original valve worked.

 

Our mongo cold snap broke today. Only 10°f now (LOL). The past few days -28°/-30°f turning on where in the valley you were. Plugin cars REALLY benefit from the ICE in that regard.
Often, the Ryobi leaf blower work well as a snow blower .... but at those temps? Forget it. The big 6ah batteries really take a beating - just like in EV's. They'd (leaf blower) be near dead in under 10 minutes.
.

 

Thread drift alert, as I go off on a tangent:

Something I've long wondered is, how fast do typical homes cool when power and heat are lost? This could be a crude metric for energy efficiency, though numerous other elements factor in too. It could also be a gauge of how long homes remain comfortably habitable when energy utilities are interrupted, something I was thinking about when planning energy improvements.

It seems there should be a very wide range of answers. My dad's house (built in 1914 with single pane windows and no insulation, and very leaky) is on the bad end of the scale. In my youth, before some modest improvements, we'd be bundling up within a half hour. Today's most efficient construction might go days.

In Bob's case, I'm guesstimating that inside temperatures dropped about 30 degrees in 10 hours, from an initial 60 degree temperature difference. Neglecting numerous other factors, this gives a heat "half life" of 10 hours. Converted to exponential parameters, that is a time constant of 14 hours, or a decay rate (similar to compound financial interest) of 7% per hour.

I had opportunity to made a similar measure of my house (1980's energy code, with several later building envelope improvements) a few weeks ago when the season's first significant snowfall, very wet and heavy, took down an uncountable number of trees and limbs and caused hundreds, possibly thousands of power outages in the region. With a presumed outside temperature overnight of 30 degrees (actual not recorded due to the outage), and initial average inside temp of 67, it fell 8 degrees in 12 hours before I fired up the woodstove. That works out to a "heat half life" of 34 hours, or exponential time constant of 49 hours, or decay rate of 2% per hour.

Has anyone else measured or estimated similar figures for their homes? Or heard of anything similar for other construction?

 

Before I installed this furnace back in 2010, I did something a little similar, where I temporarily fab'd a 10 kW electric heat element into the ductwork, disabled the gas burner, and hooked a kW meter on the heat element to a chart recorder and ran a bunch of days of charts during an especially cold part of a season (keeping some notes on the outside temperature and wind on those days). The idea was to get some empirical data to, ideally, confirm the new-furnace sizing recommendations using estimation methods like Manual J (for my 1929 house, and its exact insulation and ductwork properties).

The data could probably be massaged into a "heat half life" figure, though it lends itself most directly to a "here's a heat input rate you need to hold the temperature steady".

It ended up sort of an academic exercise, because nobody really sells a gas furnace as small as the numbers came out, and I just fudged by going for the least-oversized readily available modulating furnace, which at least can throttle itself back to 35% (nearly all of the time!) and be at least tolerably close to right-sized. The furnace will try to throttle back to a point where it can run constantly rather than cycling, but it still takes a pretty bitterly cold day for even that to be possible. (It's −10.5℃ outside now, and the furnace is running longish low-fire cycles, but still has to cycle off.)

The upside is that whenever I want to make a quick change (like coming home to a cold house in away setback), unlike an actually-rightsized furnace, this one can throttle up and make very quick work of the job.

Now, if I supplement it with a heat pump to make a dual-fuel system, it'll probably be kind of fabulous, with the heat pump a whole lot of the time, but still the extra capacity of the furnace when called for.

 

I did something similar when sizing my first heat pump almost 14 years ago. Part of it was easier with an all-electric home and having kept meter records for a very long time, including daily readings during several severe cold waves, thus having an approximate heat rate at certain temperatures. But another part was harder, as I was putting in a ductless heat pump for only part (most) of the house, needing to guess what fraction of the total heat load that represented. These systems have reduced capacity at lower temperatures, fortunately there were adequately detailed performance tables available.

As has been common with heat pump selection, I did pick an approximate "balance temperature," in the mid-20s, expecting to use supplemental heat (in our case, the original electric in-wall blowers) below that. I ended up picking one size smaller unit than the installer suggested, which was necessary (in that product line) to get the efficiency ratings that qualified for all the incentives.

After other improvements, the effective balance point seemed somewhat lower than I targeted. And in not so cold weather, the heat pump offset more electric resistance heat at the far end of the house than I had expected. So I wasn't disappointed in choosing less than the installer's initial recommendation.

That far end now has its own (smaller, but rated for colder outdoors) heat pump this year, as much for summer comfort as winter. This week, the two together held up at 12F outside, not maxed out, so none of the electric blowers needed be turned on. If/when the original unit reaches end of life, I'll make sure its replacement is also rated for colder temperatures.

While there is a strong connection between "heat half life" and steady state heat load, the translation isn't straightforward. I suspect that more people will be able to measure the former than later. But will do so only when heat and power are lost, which hopefully isn't very often.

 

One thing I would change in the youtube description:

The inducer fan is typically located on the outlet of the heat exchanger. It pulls the vent gas, containing carbon monoxide, from the heat exchanger, and pushes it out the flue. (And naturally that pulls the outside air in for combustion.)

The happy thing about that design is it keeps the inside of the heat exchanger at negative pressure. Should there be any leaks, at least it won't be pushing CO into the house at pressure.

Of course the PVC piping carrying the vent gas from the fan discharge to outside the house is at positive pressure, so that piping had better not be at all leaky.

 

Exactly why most jurisdictions now require a Carbon Monoxide Detector be installed in all spaces that have gas burning appliances

 

You should call any competent HVAC repair man who should be able to solve the problem with the truck stock. It does not need to be Lennox factory repair.

 

Lennox only sells through licensed dealers, so there are fewer sources for parts.

 

I ran into that headache with York too, several years ago, when it turned out they had fixed a problem with their condensate pan/trap, and the only way I was able to get a fixed one was a long snowy drive to a York dealer.

For some reason (maybe now that the furnace is a dozen years old) that seems to have improved a bit. To buy the gas valve I recently needed, I had little difficulty finding sources, whether of the original exact part number (for more money), or of the newer White-Rodgers "service replacement" part number (less money, better valve with improved pressure adjustment scheme).

 

over the years I've noticed that I can adjust the burners using either or both the gasline shutoff valve, which I do close every summer, as well as the furnace gas valve pilot/on/off knob. I'ver replaced a couple other things on the antique over the years ie: thermocouple, valve to pilot gas line << persnickity little devil, besides cleaning and painting the fan shroud and hamster wheel and than just cleaned the burners and heat-exchanger while checking way up there for cracks.
The other story is about the water heater I installed in 2000 the night before a flight to SanFran and it was my first and "second" attempt at sweating copper. It's still heating the household water usage too, much to my surprise, fingers crossed......

 

The heat-exchanger cracks in my old one made the most musical little pings as it heated and cooled in the burner cycles.

 

I wish I could figure out a way to quit down, when the blower shuts down after cycling. I've gotten pretty sensitive to that one over the years.
My furnace isn't as old as the octopus I was shown once in a friends house in the mid 80's, and didn't really know what I was looking at then. I've recently been curious if that old behemoth is still chuggin along and would love to get another look at it now, if it's still there.