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  1. #1

    Skeptical A/C Issue

    Hey all,

    I am looking for some advice for an HVAC issue that I have been having at one of my rental properties. I am pretty well educated on the nomenclature and process for A/C systems, but am not up to speed on pricing and proper diagnostics.

    My tenant told me in August that the A/C was freezing at the condenser, at which point I had contractor #1 take a look at it. He replaced the transformer/capacitor and added 1.2 lbs of R-22. A/C worked for a week and the problem recurred. Got a refund because the “repair” failed.

    Contractor #2 found that the R-22 was a little low and added 1 lb, but saw no evidence of leaking. The A/C worked for about 2 weeks, but the system stopped outputting cool air.
    Contractor #3 had fluctuations on his gauge so he sensed a leak or a bad metering device. He seemed very knowledgeable and I decided he’d be best suited to perform a leak check on my system. He performed a triple evacuation of the refrigerant to 500 microns and checked for leaks/noncondensables.

    (cost $)

    There were not leaks discovered and he recharged the system. This worked for about a month. He had a tech come over and diagnose the system again. This time they replaced the capacitor because it was reading low. No fix.

    We are having a different problem. Here is what contractor #3 says:

    “I just got a call from the distributor. They had to look up your coil info with the factory since its not made any more..it looks like that coil didn't come with a TXV..and for it to behave the way it is means basically that we caught the air in the refrigerant lines too late.
    We may be able to replace the coil and flush the refrigerant lines...but if the compressor was too damaged and has shavings breaking off into the lines that may need to be replaced too. It was suggested that we perform an acid test and megohm the compressor to try and determine AC longevity since the system is a bit undersized”

    After telling him that that only the fan was working and no cool air at all, this is what he said:

    “When I first put my gauges on yesterday it was acting low on charge..then it acted like a Txv open and everything went normal for an hour or so. Then before I called you it seemed as a valve had closed causing really low suction pressure and high head pressure @ the same time.
    I had told him to not use the AC and run fan only or set stat to ac and kill Pwr to AC unit for full fan speed ti prevent further damage.
    I live in a house where my system is 3/4 ton undersized..for now it work ok...but when it starts giving me problems I'm just going to replace it all with high efficiency stuff properly sized.
    I know were looking @ at least replacing the coil...possibly the compressor or condenser. It may be a good time to upgrade the system but that would require increasing the cfm by doing the furnace @ the same time. And that's your call. @ this point no matter the choice..we have to evacuate the refrigerants again. But if you upgrade the system we can credit the work we've already done to help out a bit.


    Sorry for the novel, but I really would like some input from the community. I have the feeling that contractor #3 is trying the old “hook-line-and –sinker” method with trying to get me to pay for a complete system. Its only 7-8 years old!

    Any thoughts? Thanks in advance!
    Chris
    Last edited by beenthere; 10-02-2012 at 10:02 PM. Reason: price

  2. #2
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    Over 2 pounds added to teh system. but there was no leak? Hmm, sounds like a lot of taking shots in the dark.

    Somewhat sounds like #3 is trying to sell you a new system cause they have no idea whats really wrong.
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  3. #3
    Quote Originally Posted by beenthere View Post
    Over 2 pounds added to teh system. but there was no leak? Hmm, sounds like a lot of taking shots in the dark.

    Somewhat sounds like #3 is trying to sell you a new system cause they have no idea whats really wrong.
    That's the feeling that I get. Especially becuase they changed out the capacitor and it did nothing. I can understand the upgrade if the system was 15-20 years old, but 7-8 years old seems a little pre-mature. What can I do in the mean time to squeeze some more life out of my current unit?

  4. #4
    Join Date
    Apr 2010
    Location
    NC Sandhills
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    If it didnt come with a txv it most likely has a piston or fixed orfice. If it is clogged it can cause the low side pressure to drop and high side to rise, and if a tech just looks at the low side pressure and doesnt do a decent diagnosis he will assume it is low on refrigerant. This is only an assumption on my part. Unless the system lost all of its charge at some point I dont not understand how air could have compromised the system, unless when he evacuated it (I am assuming the refrigerant that was still in the system was either pumped down into the condenser or they recovered it into a clean empty tank) he accidently broke the vacuum with air before recharging system. I dont see a capacitor being an issue in this situation. Like has been said looks like every one is shooting from the hip and #3 wants to sell you a new system. I dont think a 7-8 yr old system needs to be replaced, just fixed as its major parts most likely still under warranty. I hope for the best.

  5. #5
    Quote Originally Posted by Rodney28334 View Post
    If it didnt come with a txv it most likely has a piston or fixed orfice. If it is clogged it can cause the low side pressure to drop and high side to rise, and if a tech just looks at the low side pressure and doesnt do a decent diagnosis he will assume it is low on refrigerant. This is only an assumption on my part. Unless the system lost all of its charge at some point I dont not understand how air could have compromised the system, unless when he evacuated it (I am assuming the refrigerant that was still in the system was either pumped down into the condenser or they recovered it into a clean empty tank) he accidently broke the vacuum with air before recharging system. I dont see a capacitor being an issue in this situation. Like has been said looks like every one is shooting from the hip and #3 wants to sell you a new system. I dont think a 7-8 yr old system needs to be replaced, just fixed as its major parts most likely still under warranty. I hope for the best.
    I inquired about the piston or fixed orifice to the contractor and he stated that it was neither of those because they have been outlawed in California for a number of years. Which begs the question, what does my unit have? If the piston/fixed orifice was outlawed and, according to his email response to me from the distributor, my unit does not have a TXV, what is the device used in my unit?

  6. #6
    Join Date
    Aug 2003
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    Fort Worth, TX
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    11,290
    Quote Originally Posted by moparman915 View Post
    I inquired about the piston or fixed orifice to the contractor and he stated that it was neither of those because they have been outlawed in California for a number of years. Which begs the question, what does my unit have? If the piston/fixed orifice was outlawed and, according to his email response to me from the distributor, my unit does not have a TXV, what is the device used in my unit?
    Assuming your system has no TXV, your tech may have been baffled why the system would appear to run fine, and then suddenly show signs of a restriction. What I did not read in your post is if any of the techs who looked at your system ever bothered to remove the charge and check the piston metering device for trash. It's not that hard to do. Even before getting to that point, all of these techs could have saved themselves heartburn had they taken superheat and subcooling readings. Maybe they did...but if so they may not be interpreting that data usefully. Who knows...we weren't there.

    If you still want Contractor #3 involved, tell him you want to know what type of metering device you have (piston or TXV), and that you want it checked for trash. If he opens it up and finds none, tell him you want a new liquid line drier installed just upstream from the piston or TXV, if that's possible. If he agrees to do this, he will need to remove any old driers already in the system. This is important. Truth is, he should have already done things like this instead of you finding out about it on an internet forum. I may be barking up the wrong tree as it is, but I'm not inclined that direction at the moment.
    • Electricity makes refrigeration happen.
    • Refrigeration makes the HVAC psychrometric process happen.
    • HVAC pyschrometrics is what makes indoor human comfort happen...IF the ducts AND the building envelope cooperate.


    A building is NOT beautiful unless it is also comfortable.

  7. #7
    Join Date
    Jan 2012
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    indy
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    Quote Originally Posted by Shophound View Post
    Assuming your system has no TXV, your tech may have been baffled why the system would appear to run fine, and then suddenly show signs of a restriction. What I did not read in your post is if any of the techs who looked at your system ever bothered to remove the charge and check the piston metering device for trash. It's not that hard to do. Even before getting to that point, all of these techs could have saved themselves heartburn had they taken superheat and subcooling readings. Maybe they did...but if so they may not be interpreting that data usefully. Who knows...we weren't there.

    If you still want Contractor #3 involved, tell him you want to know what type of metering device you have (piston or TXV), and that you want it checked for trash. If he opens it up and finds none, tell him you want a new liquid line drier installed just upstream from the piston or TXV, if that's possible. If he agrees to do this, he will need to remove any old driers already in the system. This is important. Truth is, he should have already done things like this instead of you finding out about it on an internet forum. I may be barking up the wrong tree as it is, but I'm not inclined that direction at the moment.
    This is all you need to do ^^^. These are basic refridgeration issues and should be fixed without having to replace the whole system, these companies kill me these days when it come to fixing your unit if its more than a capacitor lol

  8. #8
    Quote Originally Posted by hvacmike85 View Post
    This is all you need to do ^^^. These are basic refridgeration issues and should be fixed without having to replace the whole system, these companies kill me these days when it come to fixing your unit if its more than a capacitor lol
    It’s funny you say this because on this latest service call one of hi tech’s came over and just swapped the capacitor because it read a little low. After I questioned that change but still no fix, he said that it was reading at 5% or 7%, something to that effect, and needed to get changed anyways. B.S.?

  9. #9
    Quote Originally Posted by Shophound View Post
    Assuming your system has no TXV, your tech may have been baffled why the system would appear to run fine, and then suddenly show signs of a restriction. What I did not read in your post is if any of the techs who looked at your system ever bothered to remove the charge and check the piston metering device for trash. It's not that hard to do. Even before getting to that point, all of these techs could have saved themselves heartburn had they taken superheat and subcooling readings. Maybe they did...but if so they may not be interpreting that data usefully. Who knows...we weren't there.

    If you still want Contractor #3 involved, tell him you want to know what type of metering device you have (piston or TXV), and that you want it checked for trash. If he opens it up and finds none, tell him you want a new liquid line drier installed just upstream from the piston or TXV, if that's possible. If he agrees to do this, he will need to remove any old driers already in the system. This is important. Truth is, he should have already done things like this instead of you finding out about it on an internet forum. I may be barking up the wrong tree as it is, but I'm not inclined that direction at the moment.

    This is exactly why I wanted to engage with a forum, to explore my other options. Absolutely valuable information, Thanks.

  10. #10
    Quote Originally Posted by Shophound View Post
    If you still want Contractor #3 involved, tell him you want to know what type of metering device you have (piston or TXV), and that you want it checked for trash. If he opens it up and finds none, tell him you want a new liquid line drier installed just upstream from the piston or TXV, if that's possible. If he agrees to do this, he will need to remove any old driers already in the system. This is important. Truth is, he should have already done things like this instead of you finding out about it on an internet forum. I may be barking up the wrong tree as it is, but I'm not inclined that direction at the moment.
    I asked about the metering device and he stated he would have to open up the evaporator coil to find out the metering device my system has. He said that sometimes the condenser will say if the system is a TXV system, cap tube or whatever device the system has.

    I asked him to clean out the metering device, based on your post earlier in this thread. He said that he has never had someone ask him to do that before and that it would only be a 50/50 shot at working. He said that is there was any sediment in the line that it would have been cleaned out when he did the evac, purge and refill. What do you think?

  11. #11
    Join Date
    Aug 2003
    Location
    Fort Worth, TX
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    Quote Originally Posted by moparman915 View Post
    I asked about the metering device and he stated he would have to open up the evaporator coil to find out the metering device my system has. He said that sometimes the condenser will say if the system is a TXV system, cap tube or whatever device the system has.

    I asked him to clean out the metering device, based on your post earlier in this thread. He said that he has never had someone ask him to do that before and that it would only be a 50/50 shot at working. He said that is there was any sediment in the line that it would have been cleaned out when he did the evac, purge and refill. What do you think?
    Well, I said Contractor #3 showed promise, but that may be dimming a bit.

    A seasoned tech can often tell what type of metering device is on a system without actually going to look for it. In the olden days, if a TXV was on the system, the single phase compressor had a start-assist kit on it. Nowadays, with scrolls, not always the case. However, when measuring a system, if it has a TXV on it, the superheat will remain pretty steady as the heat load on the evaporator changes and the condenser head pressure changes, whereas with a piston, the superheat will change with evaporator load and condenser head pressure. If a TXV fails, it often fails closed, as the only opening pressure on a TXV is the bulb pressure. A failed TXV will typically starve the evaporator of refrigerant, resulting in very high superheat, low suction pressure, and low head pressure.

    Of course, whether a system has a TXV or a piston metering device on it, if there is trash/debris in either device, it can act like what Contractor #3 described, where everything seemed fine and suddenly it was like someone closed down on a valve. A metering device of whichever type is the smallest passage in the system, so any trash that freely circulates in the system WILL get hung up here, if it is large enough.

    Contractor #3 needs to educate himself on what an evacuation, purge, and refill does to a system. Will it remove solid debris? On the purge phase, maybe some. Even then, only if he's doing a purge a certain way. But that is not how things are done right. To catch debris, you install a liquid line drier ANY TIME THE SYSTEM HAS BEEN OPEN TO THE ATMOSPHERE. And you flow nitrogen while brazing in that new liquid line drier, and for any other work done on the circuit that requires brazing. The liquid line drier serves two functions; it filters the system, and it catches any remaining moisture that could not be removed by a vacuum pump.

    Evacuating a system does not remove solid debris. Evacuation is for removing moisture and air (non-condensibles). Purging is mainly done with nitrogen and a product to rid the system of oil...either because oil is logged up somewhere in the system, or the tech is converting the system from mineral oil to POE oil. Purging is NOT done to get moisture and air out of the system, and it won't remove all of the solid contaminants.
    • Electricity makes refrigeration happen.
    • Refrigeration makes the HVAC psychrometric process happen.
    • HVAC pyschrometrics is what makes indoor human comfort happen...IF the ducts AND the building envelope cooperate.


    A building is NOT beautiful unless it is also comfortable.

  12. #12
    Quote Originally Posted by moparman915 View Post
    I inquired about the piston or fixed orifice to the contractor and he stated that it was neither of those because they have been outlawed in California for a number of years. Which begs the question, what does my unit have? If the piston/fixed orifice was outlawed and, according to his email response to me from the distributor, my unit does not have a TXV, what is the device used in my unit?
    I am starting to get the feeling that I am being fooled. I asked again about the metering device and he said that he could not tell what my system had without opening up the evaporator case and that he "assumed" the system was a TXV system because of the way it was behaving.

    I don't like pay professionals for assumptions, I need results...

  13. #13
    Quote Originally Posted by Rodney28334 View Post
    If it didnt come with a txv it most likely has a piston or fixed orfice.
    Do all units come with a piston, fixed orfice or TXV? Does it have to have at least one of the three to function...?

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