ReplyAlso if you look closely to your schematic you posted, the "W" wire to the gas valve has it's own limit, between the "W" on the board and the valve.
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If you don't know what sites you post on, I have no desire to refresh your memory. You even posted one of those sites on a thread on this site.Originally Posted by 54regcab
You were wrong about the power to the thermostat being cut off when a furnace goes out on high limit. There is nothing in any furnace that turns off power to the thermostat due to a limit switch opening. My stating you are ignorant of furnace functions should be taken as positive criticism and not as an insult. The only thing insulting is posting things that are not accurate.
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Also if you look closely to your schematic you posted, the "W" wire to the gas valve has it's own limit, between the "W" on the board and the valve.
__________________________________________________ _______________________
“Experience is a hard teacher because she gives the test first, the lesson afterwards" ~ Vernon Law
"It's what you learn after you know it all that counts." ~ John Wooden
"When the teachers become unteachable we're all in trouble" ~ Mr. Bill
"Remember "Pro" is only a name, it's not always a mindset determined to do everything correctly" ~ Mr. Bill
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He's misreading the schematic. According to what reg is stating, the gas valve would be constantly energized.
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Practical Training is a must!
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Would this setup work well with this much sq. ft. International Falls, Minnesota?
__________________________________________________ _______________________
“Experience is a hard teacher because she gives the test first, the lesson afterwards" ~ Vernon Law
"It's what you learn after you know it all that counts." ~ John Wooden
"When the teachers become unteachable we're all in trouble" ~ Mr. Bill
"Remember "Pro" is only a name, it's not always a mindset determined to do everything correctly" ~ Mr. Bill
Professional Member*
The issues is not wiring in a way to keep the thermostat powered up, it's getting the furnace situation corrected since it's not operating properly. We don't want to "hide the problem" by wiring in a control circuit. It makes me wonder how many systems out there with battery powered thermostats are hitting the limit and the customer doesn't even realize it.I could take that same board, add a simple N/O relay between the red stat wire on the board and the stat, so when the limit opens, the red wire from the stat to the board, is open, but the thermostat is still powered up. There is no more risk involved, than you adding your thermostat, this is the understanding of simple controls not rocket science.
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Doubt it, unless the house is REALLY well insulated. Maybe some of that super spray foam and quadruple pane windowsWould this setup work well with this much sq. ft. International Falls, Minnesota?
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Cutting the power to the thermostat means no power to the W terminal from the thermostat. The furnace may very well have an additional safety on the W terminal.
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My guess is, if the furnace it not working, that is would prompt most home owners to call for service, regardless.
You totally lost me here.
__________________________________________________ _______________________
“Experience is a hard teacher because she gives the test first, the lesson afterwards" ~ Vernon Law
"It's what you learn after you know it all that counts." ~ John Wooden
"When the teachers become unteachable we're all in trouble" ~ Mr. Bill
"Remember "Pro" is only a name, it's not always a mindset determined to do everything correctly" ~ Mr. Bill
Professional Member*
Furnaces can still "work" even though they are shutting off on high limit. They run for a few minutes, go off on limit while the blower continues to run and blow hot air into the house. Once the furnace cools it resets and runs again. As long as it's not being used near capacity a homeowner may not notice this behavior, especially if the blower doesn't completely cycle off each time.
Pre-90's furnaces like you were talking about earlier that just cut the voltage from the gas valve while keeping the blower running would just keep working as far as he homeowner knew, unless they were hearing/watching the burners cycle.
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You really need to stop posting and do a little research before you post. The old style furnaces would not keep running, when the stat was satisfied, it would kill the power to the gas valve, and then the fan limit would cool, and shut off the blower motor.
__________________________________________________ _______________________
“Experience is a hard teacher because she gives the test first, the lesson afterwards" ~ Vernon Law
"It's what you learn after you know it all that counts." ~ John Wooden
"When the teachers become unteachable we're all in trouble" ~ Mr. Bill
"Remember "Pro" is only a name, it's not always a mindset determined to do everything correctly" ~ Mr. Bill
Professional Member*
I meant on the high limit switch not thermostat. When the old furnaces hit limit what is supposed to happen?
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Still posting without some research, please find an old PDF of a wiring diagram on a pre 90's furnace, your driving me crazy with your questions.
__________________________________________________ _______________________
“Experience is a hard teacher because she gives the test first, the lesson afterwards" ~ Vernon Law
"It's what you learn after you know it all that counts." ~ John Wooden
"When the teachers become unteachable we're all in trouble" ~ Mr. Bill
"Remember "Pro" is only a name, it's not always a mindset determined to do everything correctly" ~ Mr. Bill
Professional Member*
Also, for any house that size that requires that little heat, just how much cooling is required. If that house is in an area far enough south to not need the least amount of heat that is available in a gas furnace, then a heat pump system would be the way to go, like is done in other Southern areas.Would this setup work well with this much sq. ft. International Falls, Minnesota?
Since reg is refusing to give us specifics about the applications he is claiming, we have nothing to go on in order to find out why he has so many more issues than anyone else in the country.
Training is important!
Practical Training is a must!
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The power is not cut to the thermostat when a high limit switch opens. I've never seen a furnace that cuts the power to the thermostat when a high limit circuit has opened. Follow the power from the transformer in order to understand what that circuit is doing.
Training is important!
Practical Training is a must!
Professional Member*
This is all indicative of an improperly sized duct system, air blockage such as dirty filter or coil, loss of blower capacity etc. None of this has anything to do with the furnace being oversized.
What is the point of all of this rambling of yours? What are you trying to get at?
Training is important!
Practical Training is a must!
Professional Member*
Exactly. On older furnaces, the blowers were energized strictly by temperature. I've seen furnaces in attics turn on the blower because of heat build up during the hot Summer days.
Training is important!
Practical Training is a must!
Professional Member*
You know it's one thing to want to learn the trade, and just humble yourself and sit back and watch and listen, but when your argument is not fact, and you don't just stop for a moment to research something before you post, you not going to appear to be the brightest bulb in the house. It's like me going on a TV repair forum and and telling all the pro's there how a TV works or is wired.
__________________________________________________ _______________________
“Experience is a hard teacher because she gives the test first, the lesson afterwards" ~ Vernon Law
"It's what you learn after you know it all that counts." ~ John Wooden
"When the teachers become unteachable we're all in trouble" ~ Mr. Bill
"Remember "Pro" is only a name, it's not always a mindset determined to do everything correctly" ~ Mr. Bill
Professional Member
God Speed, Jim. We'll miss you - 2-26-23
I broke out the thread so they can keep going on and the OP doesn't get a bunch of needless notifications.
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Please help me understand on the path to the 24V power to the thermostat. I've highlighted what I'm seeing on the power path, what am I missing? If LS1 were to open, how does it tell the CPU to go into "high limit" mode? The 24V powered thermostats definitely go blank and 24V to the thermostat back plate is gone when the burners go off on high limit and the "33 code" shows up. The blower continues to run while the 33 code is being displayed. Once the furnace cools back off the power is restored to the thermostat. I'd like to get to the bottom of this since I see a lot of them.
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