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  1. #27
    Join Date
    Oct 2005
    Posts
    68
    A limit usually trips due to overheating. The reason why they overheat is because you aren't moving enough air. The system has worked fine for x amount of years and now all the sudden it doesn't work properly. Sounds like something happened to your airflow. Did you move furniture and block vents, are the zone dampers opening fully, if you have a bypass damper is it operating properly. Find out if you have the correct amount of airflow.

  2. #28
    Join Date
    Jul 2002
    Location
    St Paul, Minnesota
    Posts
    3,468
    Mikej:
    Try keeping both zones calling with a setting of 80 or so. Open your windows and see if the unit will continue to run. Or if you can, manually open both zones.


    Trane:
    Have someone check the temperature rise with each zone individually. This will tell you if there is a airflow problem with any of the zones


    What I and Trane are getting at is to see why the unit is cycling off in the first place. I don't think you will waste more than pocket change trying my advice. Set both stats to 80 and let er run. Does it shut down? It shouldn't unless the tstat gets to 80 but with doors and windows open I doubt it will. If it does shut down you have an airflow problem as others have said. Get the utility company to open the plenum and peek at the underside of the A Coil. Takes about 15 minutes to peek and close back up.

    If a limit was replaced and a different length limit was installed that may make the unit stop before the thermostat is satisfied but I don't know why your blower keeps running so long. Does your limit have a dial on it? Got info on it? I've seen them stick before and who knows where the utility got that one. Off the floor of the van? Happens.

    You think you can run enough air thru the plenum with only one zone calling? Is a damper sticking? Happens. I know you didn't have this problem for five years and that is puzzeling. I have found dampers not operating correctly, the wrong ones wired to the wrong tstat etc.(Not your problem tho)

    A cheap pleated filter or let's say not real expensive one has enough surface area for most applications. You get into the 3M red and purple ones and you got issues of airflow. Techs that say use the 59cent ones got there head where the sun don't shine because all that dust collects on the blower, motor, and A Coil, not always on the filter. So too cheap is bad also.

    Today, I was in an empty house and ran the furnace. An old sixties one with the blower in back. I removed dirty filters and later noticed it was cycling on and off. The blower would run then the burners would relight with a whoosh and run awhile. Never getting the cold house past 65. Since all register were open and returns were the old large ones I checked the blower. Somewhat dirty but motor replaced in the last 3 yrs or so and was using the lowest speed. So I used another wire and ran it on medium speed. Not much noisier but it never shut down and the limit was adjustable and had been at 190. Not saying there isn't other problems yet, that will get checked later but it quit cycling off.

    You got 2 problems.
    One, it shuts off before the tstat is satisfied. Right?
    Two, the blower runs longer than it should. Right? I gave you a solution for that. Get er done, winters comin'

  3. #29
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    68,125
    Might be looking in the wrong place.

    Is it possible that although the furnace limit is opening, that it is really yoour zone panel keeping the fan running.

    Thats why I asked if it has a bypass damper.

    As some one else sort of said. You need a tech that isn't going to rush in your door, change a part and leave.

    It could be a dirty coil causing this, it could be a weak run cap on the blower, or your secondary heat exchanger is dirty on the outside. Or several other things that we on the internet can't tell from our monitors.

    I understand your not wanting to waste money, but if it continues too long, it could do some expensive damage.
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  4. #30
    Join Date
    Dec 2002
    Location
    Houston,Tx.
    Posts
    16,004
    He said the unit is cycling just fine heat on-heat off or burner on-burner off, his only issue that I read is that the fan continues to run after the stat is satisfied in the heat mode, but if he calls for heat again it will stop and work fine until the stat is satisfied again this is what I understand, it could be something as simple as a bad place in the low voltage wire, I would have to pull the stat and tie the wires together manually and see how it operates before I could rule out that it could be a stat issue.
    I might have missed something but I never read were the limit was kicking off the burners at all, only that the fan continued to run after heat cycled off.
    __________________________________________________ _______________________
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  5. #31
    Join Date
    Jul 2002
    Location
    Slacking off right now
    Posts
    7,546
    Summed up: you may have an accumulation of individual problems causing your problem.
    1. bad limit tripping at too cold a temp
    2. dirty or plugged a coil
    3. air flow issues- stuck dampers non functioning motorised dampers, registers that could be cloesed too much a by pass damper(if installed) not opening or opening too much, perhaps balancing dampers slipped closed

    Good techinicans cost money good companies hire good techs so if you want it fixed you will have to bite the bullet

    The fault indicator on the board indicates a limit switch trip - first paragraph

    [Edited by The Penguin on 10-25-2005 at 06:47 PM]
    www.vetopropac.com - The best tool bags on the market - The offical tool bag of choice by techs everywhere

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  6. #32
    Join Date
    Feb 2001
    Location
    Jackson, NJ
    Posts
    92
    Originally posted by smokin68
    Mr. Apples,
    Am I missing something here? You have a contract with the utility company, I told you to call a real service company, not trying to debate over who's better,but since the utility company can't find the problem, you should hire someone who works on furnaces. So, you state you have a contract with them,and basically don't want to shell out the $$$ to a service company. Now, you're going to have your coil cleaned without even knowing if that's the cause of the problem(more than one thing can cause the limit to trip). and then,if that doesn't work, you'll think about hiring the service company. The smart money would go on hiring the service company now......
    Herr Smokin: The only reason I'm moving toward cleaning the coil is that it seems that the pro posters are telling me that air flow is being restricted. There was no problem with the unit for five years. I'm assuming that there's now a buildup of crud on the coil and that is what's causing the restricted air flow. I appreciate your input, as I do all the posters to this forum. I figure that I have to start someplace. I'm open to suggestions; but, read all the posts...there are lots of different suggestions. I'm just trying to find a starting point.

  7. #33
    Join Date
    Feb 2001
    Location
    Jackson, NJ
    Posts
    92
    Originally posted by MikeJ
    Mikej:
    Try keeping both zones calling with a setting of 80 or so. Open your windows and see if the unit will continue to run. Or if you can, manually open both zones.


    Trane:
    Have someone check the temperature rise with each zone individually. This will tell you if there is a airflow problem with any of the zones


    What I and Trane are getting at is to see why the unit is cycling off in the first place. I don't think you will waste more than pocket change trying my advice. Set both stats to 80 and let er run. Does it shut down? It shouldn't unless the tstat gets to 80 but with doors and windows open I doubt it will. If it does shut down you have an airflow problem as others have said. Get the utility company to open the plenum and peek at the underside of the A Coil. Takes about 15 minutes to peek and close back up.

    If a limit was replaced and a different length limit was installed that may make the unit stop before the thermostat is satisfied but I don't know why your blower keeps running so long. Does your limit have a dial on it? Got info on it? I've seen them stick before and who knows where the utility got that one. Off the floor of the van? Happens.

    You think you can run enough air thru the plenum with only one zone calling? Is a damper sticking? Happens. I know you didn't have this problem for five years and that is puzzeling. I have found dampers not operating correctly, the wrong ones wired to the wrong tstat etc.(Not your problem tho)

    A cheap pleated filter or let's say not real expensive one has enough surface area for most applications. You get into the 3M red and purple ones and you got issues of airflow. Techs that say use the 59cent ones got there head where the sun don't shine because all that dust collects on the blower, motor, and A Coil, not always on the filter. So too cheap is bad also.

    Today, I was in an empty house and ran the furnace. An old sixties one with the blower in back. I removed dirty filters and later noticed it was cycling on and off. The blower would run then the burners would relight with a whoosh and run awhile. Never getting the cold house past 65. Since all register were open and returns were the old large ones I checked the blower. Somewhat dirty but motor replaced in the last 3 yrs or so and was using the lowest speed. So I used another wire and ran it on medium speed. Not much noisier but it never shut down and the limit was adjustable and had been at 190. Not saying there isn't other problems yet, that will get checked later but it quit cycling off.

    You got 2 problems.
    One, it shuts off before the tstat is satisfied. Right?
    Two, the blower runs longer than it should. Right? I gave you a solution for that. Get er done, winters comin'
    MikeJ: You hit on an interesting point...I never made it clear that the furnace was running through the heating cycle normally, i.e., the thermostat would indicate that the set temperature was reached, the little flame icon would disappear, but the blower would just keep running. It was not shutting down prematurely. I sincerely apologize for not clarifying this point earlier.

  8. #34
    Join Date
    Feb 2001
    Location
    Jackson, NJ
    Posts
    92
    Originally posted by mrbillpro
    He said the unit is cycling just fine heat on-heat off or burner on-burner off, his only issue that I read is that the fan continues to run after the stat is satisfied in the heat mode, but if he calls for heat again it will stop and work fine until the stat is satisfied again this is what I understand, it could be something as simple as a bad place in the low voltage wire, I would have to pull the stat and tie the wires together manually and see how it operates before I could rule out that it could be a stat issue.
    I might have missed something but I never read were the limit was kicking off the burners at all, only that the fan continued to run after heat cycled off.
    Mrbillpro: Exactamundo! The heating cycle works fine, it's just that the fan keeps running after the heating cycle finishes. I am still working with the original thermostats. The limit switch looks like a button battery with wires at two ends that appear to be connected where the old switch was connected. Except for the circuit board that was replaced, I have all the original parts (except for the filters which get replaced every month).

  9. #35
    Join Date
    Feb 2001
    Location
    Jackson, NJ
    Posts
    92
    Originally posted by The Penguin
    Summed up: you may have an accumulation of individual problems causing your problem.
    1. bad limit tripping at too cold a temp
    2. dirty or plugged a coil
    3. air flow issues- stuck dampers non functioning motorised dampers, registers that could be cloesed too much a by pass damper(if installed) not opening or opening too much, perhaps balancing dampers slipped closed

    Good techinicans cost money good companies hire good techs so if you want it fixed you will have to bite the bullet

    The fault indicator on the board indicates a limit switch trip - first paragraph

    [Edited by The Penguin on 10-25-2005 at 06:47 PM]
    Penguin: Funny that you should mention biting the bullet...I've been away from my reloading press for about two years...maybe this is an omen that I should start reloading again. Read my other post...I have lots of suggestions/recommendations and I figure that I have to start somewhere, which is why I figure that I should start with getting the coil cleaned. If that doesn't work, then call in a factory authorized tech to diagnose the problem, UNLESS I start witht the factory authorized tech, see what he says, and go from there.

  10. #36
    Join Date
    Feb 2005
    Location
    GEORGIA
    Posts
    1,532
    [QUOTE]Originally posted by eapples




    Right after that I bought the service contract from the utility company, and they started servicing the unit in the spring of '05

    Call a REAL PRO....


    Good Luck

    Stephen
    "Value our Differences"

  11. #37
    Join Date
    Feb 2001
    Location
    Jackson, NJ
    Posts
    92
    Originally posted by beenthere
    Might be looking in the wrong place.

    Is it possible that although the furnace limit is opening, that it is really yoour zone panel keeping the fan running.

    Thats why I asked if it has a bypass damper.

    As some one else sort of said. You need a tech that isn't going to rush in your door, change a part and leave.

    It could be a dirty coil causing this, it could be a weak run cap on the blower, or your secondary heat exchanger is dirty on the outside. Or several other things that we on the internet can't tell from our monitors.

    I understand your not wanting to waste money, but if it continues too long, it could do some expensive damage.
    Mr. Been: Thank you again for your input. There is no bypass damper. The trol-a-temp was installed so that the zone that is not calling for heat closes while the zone that is calling for heat remains open. When the heating cycle finishes, the zone that was closed then opens while the blower continues for about a minute and a half. I've observed the motorized dampers and it appears that they are opening and closing normally.

  12. #38
    Join Date
    Mar 2005
    Location
    Suppy NC
    Posts
    4,513
    it would seem to me your problem isnt the coil bing dirty even though it is a good idea to clean. you stated you have had no problem with the unit for five years and it wasnt go off on high limit till just recently. you had a guy replace the circut board and then the problem started.
    is the board wired correctly. are the blower speeds set properly. is it wired into the honeywell control correctly.
    if it has been hitting high limit since the begining you realy wouldnt know it unless you were standing in front of it. the limit may be defective and need to be replaced. or the two controls are miscamunicating incorectly

  13. #39
    Join Date
    Jul 2002
    Location
    Slacking off right now
    Posts
    7,546
    well thats a start observing the dampers operation. did they open and close fully for you, were yiou able to comfirm air flow in respect to th e appropiate zones?

    If so then see if the unit trips on one particular zone or if it trips on one zone and not the other than you may be not moving enough air in that zone. if its both then focus on your furnace fan, blower wheel, a/c coil etc.
    www.vetopropac.com - The best tool bags on the market - The offical tool bag of choice by techs everywhere

    Arguing with some people is like wrestling a pig - eventually you realise the pig actually enjoys it

    Gonads serve a useful purpose but are no substitute for brains

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