HVAC hacking

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years). The module contains some timers (redundant approved safe

A lot of wasted capacity as time goes by the way your part of the world has heated up, 60o today when 30 years ago it would have been in the 30s, and scorching hot summers...

years). The module contains some timers (redundant approved safe

I really doubt it's the chip. More likely one of the switch sensors, the thermostat or the e-caps.

What 'e said.

Yup, agree. With a lot of stuff I fixed over the years I simply re-soldered any and all solder connections and ... bingo.

--
Regards, Joerg

http://www.analogconsultants.com/

years). The module contains some timers (redundant approved safe

Where, where ... ? Want to be there, wife does not like winters and I don't either :-)

If you meant Toronto, no ten horses would drag us there. Way too cold.

--
Regards, Joerg

http://www.analogconsultants.com/

My UK gas boiler does this:-

Demand at T0. Fan blows to purge old gasses for 10 seconds and checks that there is positive pressure in the exhaust. Gas valve on, water pump starts. Spark for 5 seconds then cut off if no ignition. Boiler fires up.

If there is any air trapped in the pipes the boiler heat exchanger overheats and shuts down in a couple of minutes... This happens if I have to drain the system down... ( to add/repair radiators.) I guess your system is a hot air blower... and cold air (aircon) in the summer. Sounds like others have suggested that maybe the heat exchanger is going 'over temp' when it actually isn't....

this shuold be the other way around. Gas rushing into the mix must find a spark right away. If the spark arrives delayed ... *WHADDABOOM*

I kind of have a hunch that this board might be perfectly ok but the designers of this furnace or the installers have screwed up. For example, if there isn't enough pressure at the air circulation fan output then the heat exchange temperature can rise too fast. That can have several reasons. Sub-par duct layout, motor speed tap on the big fan selected too low, and so on.

Linnix, if the air flow is stronger (higher motor tap) when you turn your thermostat to "fan only", maybe try the heater with that. If the short-cycling then doesn't happen you'd know why :-)

--
Regards, Joerg

http://www.analogconsultants.com/

Yeah, patio weather today, and winters have been relatively mild- even to the point of little to no persistent snow by Xmas. 8-( I find a nice crisp layer of snow on a sunny day far preferable to winters consisting of frequent grey skies and regular cold drizzle in some parts of the world, but it doesn't happen so much anymore.

Still, every few years a cold mass of Arctic air comes in and you need to either have some sweaters around or a furnace capable of putting out some serious heat for a few days. At least there's usually no snow when it's seriously cold.

Best regards, Spehro Pefhany

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"it's the network..."                          "The Journey is the reward"
speff@interlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com

I much prefer 71F and sunny, like today. ;-) Winters here are just fine.

I remember the first year we were in VT. I said "I didn't know you could get a foot of snow at -20F", more than a couple of times.

A good cold snap kills off the creepy crawlies, not to mention dissuading the "Occupy" types and bums.

Wow. I can't recall anything NEARLY that cold in ages. That would rival Minnesota, wouldn't it? The snow gets crunchy, IIRC. When I was in far northern China last year it was ~-30°F in Harbin, (Heilongjian province, up near Siberia -- got a chance to wear the real cold weather gear. Two pairs of gloves (lobster style outer gloves), several layers, long underwear, Sorels with thick socks. Ice-cold beer sold in plastic bags, and ice cream bars sold out of cardboard boxes set up on tables outside. Great fun.

For real cold, these things are made up here (and about a thousand rip-off sites offer crappy counterfeits of dubious effectiveness), but they'd be way overkill for the local weather:

Best regards, Spehro Pefhany

--
"it's the network..."                          "The Journey is the reward"
speff@interlog.com             Info for manufacturers: http://www.trexon.com
Embedded software/hardware/analog  Info for designers:  http://www.speff.com

heats

g

Yes, we are running the blower at the lowest speed; otherwise, the air flow noise is too loud to watch TV in the living room. We might have to redo the duct work anyway.

The sensor going into the heat exchanger is a themo limiting switch that open at 180F and close at 150F. This is for the 4 burners furnace. The 2 burners version (which we are not using much) has a limiting switch of 250F/210F. Right now, i am testing the 4 burners with the 250F/210F switch, which seems to extend the burning time. However, it might not be too safe to run unattended with the higher temp. limit. I might try something in between, perhaps 200F or

210F. Carrier/Payne seems to have all kind of temp. switch available for different models.

Thank everybody for all the suggestions so far.

Maybe your ventures into the northern parts of China have made you tough. I would most certainly not call that a pleasant climate:

Depends on what one calls "serioulsy cold" :-)

--
Regards, Joerg

http://www.analogconsultants.com/

Bad here too, tonight... 67°F :-) ...Jim Thompson

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| James E.Thompson, CTO                            |    mens     |
| Analog Innovations, Inc.                         |     et      |
| Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    |
| Phoenix, Arizona  85048    Skype: Contacts Only  |             |
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  |
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I love to cook with wine.     Sometimes I even put it in the food.

When it extends the burn time but does not result in continuous duty until heat demand is met then I believe your duct work is really not good, and rather far from good. I would not increase the limit switch temperature, it's not safe to do that. On our gas furnace the limit switch never comes on. The burner is a serious size, 125,000 BTU, yet it runs continuously from ignition all the way until the living room thermostat says it's enough.

Overtemp can also happen if too many registers throughout the house are closed or blocked.

Regarding duct work I had an interesting episode. Guy from the furnace place comes over for the 6-month check-up, and they are all very professional. "Sir, the duct work is fairly bad, too many right angles, and it's all too narrow. We could improve that quite a bit" ... "But you guys sold the furnace and installed the duct work about 15 years ago" ... "Oh, ahm, well ..." :-)

--
Regards, Joerg

http://www.analogconsultants.com/

erheats

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ing

That is not advised. From what I've read online, that sensor is measuring the combustion exhaust stream temperature. A few reasons that could be running hot due to lack of airflow is exhaust vent obstructed or your location is so airtight ( like a cellar remodeled for high energy efficiency) the input combustion air pressure goes too negative. You might eyeball the vent path and if that's not it, open a window or two in the space to see if that corrects the problem.

I think he meant the sensor on the other side of the heat exchanger. The exhaust would be a lot hotter :-)

250F sound way too high for this though. The ones I have seen had a high limit of around 170F. But that high limit contact is never supposed to trip off. If it does then something is probably wrong with either the equipment or the installation.

--
Regards, Joerg

http://www.analogconsultants.com/

We have had 2 homes that had cycling or temperature issues. In both cases the registers opposite the thermostat had to be closed to allow the thermostat to operate properly, especially in very cold or warm weather. One register was on the other side of a 14' wide room, and the other was in a bath across the hall from the thermostat. In either case the periphery of the house was cold or warm with out side temperature extremes until the registers were closed.

Older mechanical thermostats had anticipator heaters that had to be current matched with the gas valve for best hysteresis. The thermostats had small manual rheostats to set the current as stated on the valve. New electronic thermostats have a variety of schemes for anticipation function.

Some of the delay in fan on and off results from the time constant of the temperature switch.

There's a difference?

I'm constantly surprised by the lack of creepy crawlies here. Some spiders, sure. Ants out the ying-yang, yes, but Amdro does a good job on them. I think I got one mosquito bite all year, and that was in October. I thought we'd have ride-on cockroaches (Palmetto Beetles) but nope. Haven't seen one. Of course armadillos replaced woodchucks on the side of the road and there are deer everywhere (no limit on does, even).

The lowest I remember it being while we were living in VT was -34F. I was in Silly Valley at the time but I heard all about it when I got home. Boy, did I!

Yeah, snow gets really crunch below about -10F. At -20F salt doesn't work at all but they spread it instead of sand. Sand turns back to rock long before that. That first year we had so much snow and it was so cold there was no way to remove the snow so we drove on it for a few weeks until it got above zero. There was a foot of packed snow on the roads and another 3-4' piled up around all of the intersections. Fund driving. There was enough snow such that my (new) snow blower wouldn't throw it over the banks so my driveway started getting smaller. Like you say, great fun! Again, I like it down here. ;-)

Nice stuff, to be sure. I still have a coat but haven't worn it for three years (since my mother's funeral in IL - another great place to be FROM).

I serviced a Lennox HE gas heating system for a neighbor. HVAC contractor wanted over $300 to replace the control module. I found an open solder joint on one of the relays. Joint had failed where the relay was soldered to the single sided board. Re-soldered and spiffed up the mounting. Been working two seasons perfectly now.

On these, there is an elaborate series of interlocks to make sure things happen in sequence and shut down when things are not right. One important thing is the flame sensor (Klixon switch) in the combustion air intake plenum. If there is a chimney blockage, the flame backs out into the air intake and trips the sensor causing a shutdown.

There is also a Klixon switch on the hot air plenum that is not supposed to run the fan until the plenum is hot. Even if this is working, cool air may be expelled from the ducts just from volume of cool air that the ducts hold. Some systems have multi speed fans that initially circulate on low speed to purge cool air and then go high speed when filled with warm air. Another klixon switch detects if the hot air plenum is too hot like if there is a fan failure or duct / filter blockage.

I was able to google for the Lennox model number and found a schematic of the system (not the control board - it's a black box as far as the manufacturer is concerned). It was pretty easy to sketch out the board anyway.