limit switch misc? will try it all


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Old 11-22-09, 08:50 PM
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limit switch misc? will try it all

with the help of this forum and forums like it, i am becoming addicted to fixing things. it helps that i am extremely miserly and don't want to pay anyone anything for something i can learn to do myself.

i am excited to make my first contribution, and so we confront my york diamond 80 oil furnace where the intake is down low, blowing upwards.

it has been a good ride. first, knowing nothing, it took me quite a while to discover that the flame sensor was missing this fall. why it was missing i have no idea, but it was gone. i ordered one, installed it, and got the system working.

kind of. there still seems to be some communication problems between the call for heat and the blower. explanation:

problem number one is that the heat runs correctly for some cycles, but the blower continues to blow after the heat has done its job and no longer turns on. the LED flashes continuously when this happens, and I can't find a key for that trouble code. also, turning the heat off at the thermostat control doesn't turn off the blower. i unplug it to turn it off. when i plug it back in, everything works correctly again, at least at first. this is an intermittent problem. if the heat is turned up good and high, it seems to work correctly, at least for a longer time. occasionally, it seems to work just fine, but for no more than one day at a time. (mind you, it's Louisiana and we don't really need the heat yet.).

problem number two actually happened first, back when I thought the flame sensor fixed everything. spontaneously one night, something started clicking as if it wanted to turn on but then was ordered not to. the blower motor didn't start. i can't remember the trouble code then unfortunately. it was before i knew to count the LED flashes. after unplugging the unit, after manifesting that first time and then maybe one more time the next day, this problem number two hasn't returned.

I should add that when I put in the flame sensor, everything seemed to work. After problem number two happened, I also had to adjust the flame sensor slightly (making a small angle for it to be heated more directly) in order for the flame sensor to communicate the correct signal. I think it was after I did this that we haven't experienced problem two at all.

Currently we are stuck at problem one. AFter reading up on it, I am thinking that a limit switch is an important part of the solution. Either the limit switch is doing its job and there's something I need to address, or perhaps it's not working properly.

I went to another house today and looked at it's furnace, and saw the limit switch and everything made sense, in relation with this webpage: Furnace Fan Limit Switch Control: a guide to the fan limit switch, settings, manual fan override, temperature settings for warm air heating furnaces - Honeywell L4064B Combination Fan and Limit Switch .
however, my furnace is not like that. going by the wiring scheme, it has two limit switches on the blower assembly and one other, and it doesn't look like the limit switch with the dial etc, it looks like an upside down texas instruments black plate with 1004 on it.

I don't know where to go from here, but I'm willing to try it all.
 
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Old 11-23-09, 05:32 AM
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p.s., i wrote oil furnace, but this furnace uses natural gas.
 
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Old 11-23-09, 06:36 AM
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A good place to start would be by posting the make and model of the furnace, which can be obtained from the rating plate located in the burner compartment of the furnace.

The make and model of the ignition control module would also be useful.
 
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Old 11-23-09, 07:47 AM
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york diamond 80 serial # P1ckd12n06401a

the ignition control module: The only identification i can see around there is something like an A and G and various #s.

I took some photos, but how to get them to post on this forum is another how to project.
 
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Old 11-23-09, 07:53 AM
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Old 11-23-09, 08:16 AM
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Check again on the model number, please. It probably starts with a P, G or L.

I think this is the manual for your furnace, but the model number will tell for sure:

http://www.yorkupg.com/PDFFiles/035-...001-A-0404.pdf
 
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Old 11-23-09, 08:49 AM
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I guess the model # is p1ckd12n06401a and the serial # is eamf021761. it is upflow. oh! and here's a date, 1995, but I don't know if that's the age of the model.

the manual diagrams are similar, but the control board (and blower motor) is beneath the other stuff.
 
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Old 11-23-09, 05:33 PM
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Could you illuminate the wiring diagram and photo it again?
 
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Old 11-24-09, 05:19 AM
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Old 11-24-09, 08:48 AM
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LS 1 = primary limit switch. L2 and L3 are the limit switches on the blower. RO are your roll out switches. LP with the C and NO designation, to the right of those 2 limit switches 1,2 and 3, is your pressure switch All these have to be "closed" for 24 volts to continue to gas valve.

Look at your bottom schematic, and you will see. Now knowing that you can see where power gets lost at first, in that chain.

LS1 is first in the chain....on down to the gas valve relay, which is last. If primary LS1 gets lost, everything (24 volts)else downstream gets lost. Therefore, use voltmeter to see if you at least get 24 volts to the one incoming wire on LS1. If it is there, and not on the outgoing wire of LS 1, then you will have an open 24 volt ac safety circuit all the way through all the other limits and roll outs on through the gas valve. IF you have power through LS1, yet a blower limit switch goes out - well let us know where the power gets lost at, whether at the primary # 1 limit, or at either of the two other blower limit switches, or at the pressure switch.

These tests must be conducted while there still is a call for heat, and yet the furnace (burners) shut off and the house registers blower fan is the only thing running.

To test with voltmeter, test between only one spade connector on a switch, to unpainted metal of the furnace - at a time. Then do the other spade connector test the same way. That way you wil know if just one wire has 24 volts, or if two wires do, or no wires do. If two wires do, you have passage (good, we want that) of current at that switch. But if only one wire, that means 24 volts is incoming, but the switch is open, not allowing passage. If neither wire has juice, then power is lost upstream.
 
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Old 11-24-09, 11:53 AM
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I will tackle this soon and report my findings.
 
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Old 11-28-09, 07:31 AM
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I have a lot to report:

The basic finding is that there was no voltage at all going to LS3 (or anywhere downstream of course) when there should be a call for heat and the blower was going.

but look at the finer details:

11/28/9
everything runs fine up to temp. the flame turns off when temp is reached, but blower never turns off and circulating the cooler air quickly cools down the house without the flame ever kicking in. i checked the voltage of components at this time, and everything checked out with power (24-26v), both sides of everything i could test.
i reset the system by opening the bottom door, tripping the door switch. everything turned on again correctly when i put my clamp on the door switch. then the above symptoms occured. this time, however, there is no voltage to LS3 (or downstream of course). i thought surely i was doing something wrong, but pulled the plug and tested things while it was working and got expected values.
the above (no power to LS3) has happened a couple times with the same testing results.

a few days ago, when i first got the multimeter, i couldn't check the problem, because everything was working fine. but was it really working fine? here are some details:

11/24/9
flame won't stay lit!
reset, adjust flame sensor (notice it could have been shorting at bottom)
runs fine...

Also today at first the flame didn't stay lit the first time, but when i manually held the sensor a titch "this way" it worked and no problems with the flame catching immediately after the glow light ignitor thereafter.

final note: the blower blows even if i turn the unit off at the thermostat control. to reset it i have to unplug it.
 
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Old 11-30-09, 07:48 AM
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Does LS3 have temperature numbers printed on it?, so you maybe can remove it, simulate temperature with a hairdryer blowing on it and a thermometer next to it at the same time, to see if it only opens at the temp printed on it?, and not some temp below that number? If it said say something like 160-40, that means it would open(shut off) at 160, but would close (come back on) 40 degrees less, at about 120. If the limit stat checked good, then you have something that is causing heat to build up in the furnace, that has to be looked into. Various causes like poor drafting(various reasons), plugged exchanger, water in secondary exchanger, dust blocked secondary exchanger coils, dust blocked air conditioning coils(if applicable) above the furnace, dirty filter, too many registers or duct dampers closed down or blocked.

There are many furnaces out there today which do not have these types of limit stats on them. I had to deal with these things though in mobile home furnaces years ago, and saw a lot of failure, and replaced many.
 
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Old 11-30-09, 08:50 AM
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According to the photo of the wiring diagram you provide, LS3 is energized by the W contact on the circuit board. Since your say it's not getting power, the W contact is presumably not being energized. Is that correct?

If so, the thermostat isn't turning on. When the thermostat is turned up, it should switch power on from the R contact to the W contact.
 
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Old 11-30-09, 01:36 PM
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Originally Posted by SeattlePioneer
According to the photo of the wiring diagram you provide, LS3 is energized by the W contact on the circuit board. Since your say it's not getting power, the W contact is presumably not being energized. Is that correct?

If so, the thermostat isn't turning on. When the thermostat is turned up, it should switch power on from the R contact to the W contact.
What you say sounds correct to me. So a switch in the thermostat seems to be faulty. Replacing it seems a good choice. I find them online for just over $30, and mercury-free, too. Are there any checks you suggest I do before I get the replacement?
 
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Old 11-30-09, 01:51 PM
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Originally Posted by ecman51`
Does LS3 have temperature numbers printed on it?, so you maybe can remove it, simulate temperature with a hairdryer blowing on it and a thermometer next to it at the same time, to see if it only opens at the temp printed on it?, and not some temp below that number? If it said say something like 160-40, that means it would open(shut off) at 160, but would close (come back on) 40 degrees less, at about 120. If the limit stat checked good, then you have something that is causing heat to build up in the furnace, that has to be looked into. Various causes like poor drafting(various reasons), plugged exchanger, water in secondary exchanger, dust blocked secondary exchanger coils, dust blocked air conditioning coils(if applicable) above the furnace, dirty filter, too many registers or duct dampers closed down or blocked.

There are many furnaces out there today which do not have these types of limit stats on them. I had to deal with these things though in mobile home furnaces years ago, and saw a lot of failure, and replaced many.
The switches L3 and L2 don't look like that, except perhaps from inside the blower compartment. Since I can't detect an error in them--only an error before them, I'll assume for now that they're okay, but we'll come back to them later as you suggest if the thermostat switch doesn't turn out to be the culprit. I will mention, though, that the furnace doesn't seem too hot ever.
 
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Old 11-30-09, 02:21 PM
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Originally Posted by troydanielbecke
What you say sounds correct to me. So a switch in the thermostat seems to be faulty. Replacing it seems a good choice. I find them online for just over $30, and mercury-free, too. Are there any checks you suggest I do before I get the replacement?
Yes. I'd use a wire to connect the R and W contacts, which should turn the furnace on just like turning the thermostat up.

If that turns the furnace on, I'd look carefully at the thermostat and wiring to the thermostat for defects and problems.
 
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Old 11-30-09, 03:31 PM
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Originally Posted by troydanielbecke
The switches L3 and L2 don't look like that, except perhaps from inside the blower compartment. Since I can't detect an error in them--only an error before them, I'll assume for now that they're okay, but we'll come back to them later as you suggest if the thermostat switch doesn't turn out to be the culprit. I will mention, though, that the furnace doesn't seem too hot ever.
Do you have 24 volt power to L1?
 
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Old 11-30-09, 05:23 PM
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Originally Posted by ecman51`
Do you have 24 volt power to L1?
Everything seems to work fine up for the first cycle, except that when the desired temperature is attained and the furnace turns off, the blower fails to turn off. It won't even turn off when the thermostat is switched from "heat" to "off". When I checked the other day, during the first cycle, all the limit switches have 24 volt power on both sides. However, after the heating system shuts down and the blower persists, none of the limit switches have any voltage at either side. ...
 
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Old 11-30-09, 06:04 PM
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Originally Posted by SeattlePioneer
Yes. I'd use a wire to connect the R and W contacts, which should turn the furnace on just like turning the thermostat up.

If that turns the furnace on, I'd look carefully at the thermostat and wiring to the thermostat for defects and problems.
Connecting R & W did turn the furnace on. I looked carefully at the thermostat wiring, and everything checked, although there were two places of concern--a splice job and a couple wire ends on the thermostat board that were too close by my eye. I cleaned a little dust and a dog hair off of things and put it back together and the first test has everything working fine. I'll run more cycles and report back my findings....
 
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Old 11-30-09, 06:27 PM
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If ALL the limits don't even have power coming INTO them, then the reason the blower stays running is NOT from say high limiting. But the blower keeps running because since the 24 volt circuit is lost, it is treating it the same as if the high limit shut off from furnace overheating.

So now we ask why no power TO even the first limit along the path. Well, if the 24 volt power is killed like at the stat, that could do it. Or bad connections, bad board.....several things I guess.....IF 24 volts makes it way out of furnace terminal W during call for heat, to C (common or good ground). But if this W-------->C gets lost when burner shuts down and blower runs on and no 24 volt power to limit swithes, then it would likely be thermostat or it's wires, related.

Keep us updated on if furnace now works due to some coincidence or if by you bumping wires at connections that maybe you made some better connection.
 
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Old 12-01-09, 07:44 AM
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and... the problem persists

Last evening the system was working like a dream, through untold number of cycles, temperature adjustments, and the whole nine yards.

This morning after the first cycle, the blowers remained on. I put the battery back in my multimeter and checked some voltage. At first, before I opened the panel door to trip that switch, I checked LS1 and the pressure switch. Both of these had voltage at both sides! This was on the first malfunction.

Then I opened the bottom panel door (to access LS2 and LS3) and then clamped the panel door switch and then turn the system on until the malfunction occured. This time, no voltage came to W or downstream to any limit switches et cetera.

Each malfunction ends in a continuous LED flashing indicating according to my unit "flame--no call for heat", and is reset by pulling the system plug out of the outlet.

Am I still plagued with flame sensor problems perhaps? Going by that wiring diagram, I see it on the connection diagram but it is unclear to me how it fits in with "checking" or "controlling" the circuit. It is touchy and I have had to adjust it a little here and there, though no adjustments in the last few days while I checked the thermostat wiring.
 
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Old 12-01-09, 09:55 AM
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Unfortunately, you still don't have a clue as to how to check what's happening with your furnace, and it's burdensome to try to explain testing procedures when you don't have a clue.

You still haven't been able to figure out if the thermostat and wiring is turning power on to the W contact, or whether you are losing voltage at the R contact.
 
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Old 12-01-09, 02:25 PM
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Originally Posted by SeattlePioneer
Unfortunately, you still don't have a clue as to how to check what's happening with your furnace, and it's burdensome to try to explain testing procedures when you don't have a clue.

You still haven't been able to figure out if the thermostat and wiring is turning power on to the W contact, or whether you are losing voltage at the R contact.
Really? Well anyway, what is happening sometimes when the blower persists is that the W contact has voltage. Sometimes when the blower persists it does not. As I reported before, connecting the W and R fires up the system. The thermostat and wiring check out fine, at least some of the time.

There are some questions I still have that don't involve testing procedures. I wonder about how the flame sensor integrates into the circuit, and I wonder about the meaning of the code "flame--no call for heat".
 
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Old 12-01-09, 02:57 PM
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Just to take your last post as an example, you propose to go charging off in four different directions. You aren't willing to follow a purposeful diagnostic procedure to identify the problems you may have.

That's typical of DIYers, but it's not an effective way to solve problems.
 
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Old 12-01-09, 03:13 PM
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Originally Posted by SeattlePioneer
Just to take your last post as an example, you propose to go charging off in four different directions. You aren't willing to follow a purposeful diagnostic procedure to identify the problems you may have.

That's typical of DIYers, but it's not an effective way to solve problems.
I love purposeful diagnostic procedures and seek one. In my last post I reported observations and sought additional information, is all.
 
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Old 12-01-09, 03:18 PM
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troy,

When the blower will run-on with power either to W or not to W......are you making sure the stat is turned up high enough so that the stat is not shutting off?

How long will the air circulation blower run-on for?: Indefinitely?

When the flame sensor is working, and the circuit board receives the miniscule current from it, this is what allows the gas valve to remain on. And if the gas valve is on, causing heat in the heat exchanger, the blower also will run. If the flame sensor current is lost, the gas valve immediately shuts off. IF the blower had already started up on a fan timer, I'd expect the fan to shut off within about a minute. But maybe not, depending on it's (possibly adjustable) settings. Maybe it's possible that the blower will run-on for 5 minutes. But it should shut off. If you have no fan timer, and instead the blower turns on due to heat build up in the exchanger, from a fan switch, then the blower may not even come on. Because generally when flame sensors go out, the flame only lasts 3 or 4 seconds. Not long enough to generate much heat in the heat exchanger. When the flame sensor goes out, the furnace may try to ignite 3 times before finally giving up, and going into a permanent lockout. Only turning off the furnace wil reset it so you get your 3 more chances of ignition attempt again.
 

Last edited by ecman51; 12-01-09 at 03:33 PM. Reason: added large last paragraph in answering troy's question
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Old 12-01-09, 04:03 PM
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Originally Posted by ecman51`
troy,

When the blower will run-on with power either to W or not to W......are you making sure the stat is turned up high enough so that the stat is not shutting off?

How long will the air circulation blower run-on for?: Indefinitely?
Now, "unfortunately", it is working perfectly again.

About your first question: The continuous blower cools down the temperature quite quickly, so the thermostat should or would normally kick on from the temperature being low. Next time I get a chance I will adjust the temperature up or down during the problem to see if that alone will trigger a response. To be clear, though, the flame turns off at the right time, according to the thermostat--it's just that the blower doesn't follow suit (normally it shuts off about a minute or so after the flame).

As for the blower, it will run indefinitely it seems.
 
 

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