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Thread: We heard a loud boom and now it smells

  1. #1
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    We heard a loud boom and now it smells



    Carrier RTU, not 100% positive why this happened but apparently compressors & coils were replaced 2 years ago. My understanding is the metering device is like tack welded or like notched in place for this model and their known for it. Or something else went terribly bad or someone fudged up. Longtime lurker, recently active, love this forum.

  2. #2
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    That type of metering system is called a short orifice header.
    We can talk about that more in depth in a different part of the site, when you join the ranks.

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    Quote Originally Posted by jpingram55 View Post


    Carrier RTU,My understanding is the metering device is like tack welded or like notched in place for this model and their known for it. Not sure what that means.
    Do this work long enough you will see pins blows occasionally, nothing new about it. Weak connection, moisture, ??? you never really know. BUT you don't want to be standing near it when it occurs, not a pleasant experience.
    It`s better to be silent and thought the fool; than speak and remove all doubt.

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  5. #4
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    pumped down into a deep vacuum
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    Carrier's Acutrol metering device.
    Attached Images Attached Images  

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  8. #6
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    What is the plan to repair it? My opinion would be that it's time to stick a fork in it. At this point you really have no way of knowing if your theory of plugged up orifices are what caused it, but I'd say that's a pretty good guess. What usually happens is that some of them plug up (which you can usually tell pretty easily by feeling which ones aren't getting cold when the thing is running). Then someone compensates by pumping extra refrigerant into the thing. Then after running like that for a while, the compressor will take a giant dump and then you'll have a big mess to clean up.

    Carrier is very proud of the new header/orifice assemblies. It's been a few years, but I remember it was LOTS of money to buy a new one.

    They can be taken apart and cleaned if you have a helper and can't get them to bite for replacing the RTU. Just have to get in there with a torch and try to unsweat the thing from the evaporator one tube at a time, and then you can take a small piece of wire to try clear the orifices. A tiny pipe cutter and a bunch of 3/8 couplings would probably work too.

    After you get the header apart, figure out a way to blast through the coil backwards with a bunch of nitro, or maybe rx11 and then nitro.

    Like I said though, it would sure be easier and better to sell them a whole new rooftop unit if possible.

    Good luck!

    Oh wow, just noticed that thing's a heat pump. Don't think I've ever seen a heat pump RTU before. Not too many of those where I live. I'm guessing that header does double duty to become the metering device for heating mode when the refrigerant changes direction, or is there a separate metering device for the outside coil?
    Last edited by ammoniadog; 07-26-2020 at 12:58 PM.
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  9. #7
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    Quote Originally Posted by ammoniadog View Post
    What is the plan to repair it? My opinion would be that it's time to stick a fork in it. At this point you really have no way of knowing if your theory of plugged up orifices are what caused it, but I'd say that's a pretty good guess. What usually happens is that some of them plug up (which you can usually tell pretty easily by feeling which ones aren't getting cold when the thing is running). Then someone compensates by pumping extra refrigerant into the thing. Then after running like that for a while, the compressor will take a giant dump and then you'll have a big mess to clean up.

    Carrier is very proud of the new header/orifice assemblies. It's been a few years, but I remember it was LOTS of money to buy a new one.

    They can be taken apart and cleaned if you have a helper and can't get them to bite for replacing the RTU. Just have to get in there with a torch and try to unsweat the thing from the evaporator one tube at a time, and then you can take a small piece of wire to try clear the orifices. A tiny pipe cutter and a bunch of 3/8 couplings would probably work too.

    After you get the header apart, figure out a way to blast through the coil backwards with a bunch of nitro, or maybe rx11 and then nitro.

    Like I said though, it would sure be easier and better to sell them a whole new rooftop unit if possible.

    Good luck!

    Oh wow, just noticed that thing's a heat pump. Don't think I've ever seen a heat pump RTU before. Not too many of those where I live. I'm guessing that header does double duty to become the metering device for heating mode when the refrigerant changes direction, or is there a separate metering device for the outside coil?
    Separate piston. Pistons get unseated via reverse flow allowing it to bypass.

  10. #8
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    Quote Originally Posted by ammoniadog View Post
    What is the plan to repair it? My opinion would be that it's time to stick a fork in it. At this point you really have no way of knowing if your theory of plugged up orifices are what caused it, but I'd say that's a pretty good guess. What usually happens is that some of them plug up (which you can usually tell pretty easily by feeling which ones aren't getting cold when the thing is running). Then someone compensates by pumping extra refrigerant into the thing. Then after running like that for a while, the compressor will take a giant dump and then you'll have a big mess to clean up.

    Carrier is very proud of the new header/orifice assemblies. It's been a few years, but I remember it was LOTS of money to buy a new one.

    They can be taken apart and cleaned if you have a helper and can't get them to bite for replacing the RTU. Just have to get in there with a torch and try to unsweat the thing from the evaporator one tube at a time, and then you can take a small piece of wire to try clear the orifices. A tiny pipe cutter and a bunch of 3/8 couplings would probably work too.

    After you get the header apart, figure out a way to blast through the coil backwards with a bunch of nitro, or maybe rx11 and then nitro.

    Like I said though, it would sure be easier and better to sell them a whole new rooftop unit if possible.

    Good luck!

    Oh wow, just noticed that thing's a heat pump. Don't think I've ever seen a heat pump RTU before. Not too many of those where I live. I'm guessing that header does double duty to become the metering device for heating mode when the refrigerant changes direction, or is there a separate metering device for the outside coil?
    I've read on here a while ago about people drilling out the back of the header to gain access for cleaning the orifices. And then brazing up the hole. Don't remember how they were dealing with any drilling swarf, maybe another hole at bottom of header and blowing it out...

    Anyway, new header isn't 'that' expensive and replacing them is really quick if cut each line individually before unbrazing the old one out.

    Also, it's almost comical how many clogged Acutrols you find, especially on units that have had previous repairs.

  11. #9
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    Quote Originally Posted by Lahrs View Post
    Also, it's almost comical how many clogged Acutrols you find, especially on units that have had previous repairs.
    I agree. What a crappy design. To have so many orifices, that means that the size of each hole must be way smaller than it would have been if they could have just used one orifice instead. Then, just for added crappiness, they usually use one of those tiny spun copper things instead of a real filter dryer.

    Thankfully, I believe Carrier might have abandoned this idea. I might be wrong here, but I think most of the newer ones that I've seen all have TXV's instead.
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  13. #10
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    Quote Originally Posted by ammoniadog View Post
    I agree. What a crappy design. To have so many orifices, that means that the size of each hole must be way smaller than it would have been if they could have just used one orifice instead. Then, just for added crappiness, they usually use one of those tiny spun copper things instead of a real filter dryer.

    Thankfully, I believe Carrier might have abandoned this idea. I might be wrong here, but I think most of the newer ones that I've seen all have TXV's instead.
    Still making them. Had a few rooftops I did commissioning on last week that had them.
    Some have txvs though.

  14. #11
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    Thread Starter
    Were trying to get them to go with new but who knows. There are 3 units like this on the roof, with another exactly like this, down to 1 compressor.

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    I remember a nightmare MANY years ago ( 1985 - 1987 ) had a YORK RTU Heat Pump with a check valve header similar to what your pic shows . It still wakes me up at night !

  16. #13
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    As I have to guess: my first one would be the last compressor was replaced after a burn-out and the system was not cleaned up well enough when this compressor was installed.

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    Quote Originally Posted by jpingram55 View Post


    Carrier RTU, not 100% positive why this happened but apparently compressors & coils were replaced 2 years ago. My understanding is the metering device is like tack welded or like notched in place for this model and their known for it. Or something else went terribly bad or someone fudged up. Longtime lurker, recently active, love this forum.
    PHM
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    Socialism is a zombie. It never dies - even though it is constantly decaying and decomposing.

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  18. #14
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    From the title I originally thought this thread was going to be a joke about farting.
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  19. #15
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    Years ago had that happen at a McDonald’s. Was second rtu so on tall curb. When I showed up disconnect was off. I opened door and not thinking at all turned disconnect on. Pin blew out of compressor terminal about a foot from my head with flaming oil. I wiped my ass went down and said until you allow ductwork to be fixed it’s done. (Had been ongoing issue ) They fired our company and the next company. Now building is vacant. Never again turn on disconnect I didn’t turn off.

  20. #16
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    you live and learn thank goodness you were ok could have been much worse question is who turned the disconnect off in the first place another company or mcdonalds manintance man?

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