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  1. #27
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    Sep 2007
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    Quote Originally Posted by BNME8EZ View Post
    It could be low on refrigerant, or it could be a flow/distribution issue.
    I will second this, seen this a lot when charge is low.
    UA Local 32 retired as of Jan 2020

  2. #28
    Join Date
    Jan 2020
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    Thread Starter
    Ok, thanks for all the info. Tech is coming out next week to look into it further.

    I did notice something odd today when monitoring the heat register temps. After icing up for half a day, I was getting a 10 degree F rise 15 mins after auto defrost, and after defrosting the coils manually I was then getting a 20 degree rise (outdoor temp 35F). I assumed the coils had lost 50% efficiency due to the frost, but then after the next auto defrost the temp rise was back down to 10F after 15 mins.

    So I'm wondering if a partially stuck reversing valve is causing the problem, and it got unstuck when I used hot water to defrost it inside. We were told a year ago that we had a sticking RV, but they didn't replace it (different company)...they just cycled it a number of times which they said fixed it. Since then it has been cleaned (when new air handler installed).

    It's the kind of thing that might be difficult to track down, if it only happens during cold weather and it's warm when they come to diagnose the problem, so I'm just wondering if this is a possible explanation. Do faulty RVs sometimes stick in cold weather?

  3. #29
    Join Date
    Jan 2014
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    New England
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    So when you completely defrosted the complete OD coil 100% with hot water, inside and outside of the coil did you notice if the distributor tubes just after the OD metering device start frosting immediately or soon after?

    This thread keeps going and going around in circles. There are ways to somewhat check temperature difference on the RV to see if it’s shifting 100%.

    Again look at the OD metering device for immediate frosting ( heat mode ) with a 100% clear coil and the distributor tubes.

    IMO, recover total charge and weight it. Then compare to what the weight in method that Goodman wants in winter mode to charge your system by. Replace drier again, add virgin refrigerant. Looks to be 109 ounces, which includes a matching ID coil and 15’ of properly sized lineset ( should also say the amount on the OD unit electrical data plate ) for the 1.5 ton OD unit, and for every feet above 15’ of 3/8” OD liquid line you add a certain amount of refrigerant. Elevate the OD unit if possible. Then take it from there. While system is open blow nitrogen all which way but loose, ( providing OD metering device checks out OK worst case they can remove OD metering device while blowing nitrogen all which way ) Then observe the before ( your unit operation now ) and after, the distributor tubes downstream of the metering device.

    They can simulate to start a defrost and let the machine terminate by itself to make sure the defrost is working, typically you’ll see the water mist vapor elevating off the unit while in defrost if it’s wet. Also you can check the supply air temperature coming out of the closet supply vent nearest the Air Handler ( if no electric heat coming on ) the air temperature should get quite cold, while in defrost.

    Goodman wants the weight method for charging in winter time, not add a little refrigerant, remove a little refrigerant ,check pressures, check superheat, subcooling or whatever. It says that in the install guide.

    Anyway that’s my worth.
    Last edited by Bazooka Joey; 01-17-2020 at 10:26 PM.

  4. #30
    Join Date
    Jan 2020
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    With the coils partially frosted up after the auto defrost, the capillaries from the TXV frost up within about 5 mins. Will check with a clean coil.

    No steam comes off after the auto defrost, but that did happen last year. It's set to 30 mins with delay, and defrost doesn't last long...30 sec delay with compressor off, then compressor comes on for 10 or 20 secs, then off for 30 secs delay. It is doing something, as it completely removes all frost from the top half of the coil. I'm guessing it doesn't take long for the coil to reach the 75F termination temp. Temp sensor was apparently checked recently and found ok.

    Last year I think defrost was set to 60 min with no delay, and the defrost lasted about 5 mins with steam coming off at the end.

    Pouring hot water on the RV without cleaning the coils didn't seem to have any effect on heat output. I'll just mention it to the tech and he can check it properly. It was definitely sticking a year ago, and then some dirt cleaned out of it when the new air handler was installed.

  5. #31
    Join Date
    Jan 2014
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    New England
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    Gave you the factory charge for a 1.5 ton OD unit as you mentioned you had a 1.5 ton OD unit in post 13 . In post 17 says you have a 2 ton OD unit, which shows to have a factory charge of 99 ounces. Can verify at the OD unit data plate.

    You sure they reinstalled the defrost sensor in the exact position as the factory, as I’m guessing it was removed to avoid damage when they removed the factory drier, which is in the same area no?

    Maybe try going back to no delay ( non smart shift ) for test purposes, and even the 60 minutes once you figure out your issues. I only ever seen once a restricted OD coil, and that was due to ( R22 unit ) the rookie tech soldered ( soft soldered ) the lineset with so much solder that beads or small pellets of solder got lodged into the distribution tubes. Defrost of OD coil was always incomplete, even in regular heat the air temperatures where a little cooler than normal. Had Technical Rep. come out and after some temperature and pressure readings they condemned the coil. They gave the person a new OD unit, once installed system worked fine.

    When the OD coil is completely clear do you get good air temperatures out of your supply registers on a day like 35+ degree OD temperature? I suppose if the system been like this from day one that may be a hard question to answer as you don’t have anything to compare it to.

  6. #32
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    Aug 2009
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    Beatrice, NE
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    Defrost should normally take 5-10 minutes unless it is above 30 ODA. Your post about a 30 sec delay then the compressor on for 30, then another delay does not sound like a proper defrost sequence. As said it may have to do with sensor location.

    As for the Rev. Valve, if it is only a problem shifting when it is cold there is a simple fix which can help it so it shifts better. It could also be that the RV is a symptom and not an issue. Being low on refrigerant can cause shift issues with RV's, not enough pressure to get it to move.

    A knowledgeable tech should be able to diagnose this for you fairly quickly.

  7. #33
    Join Date
    Jan 2020
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    Thread Starter
    Yes, I see we have a 2 ton unit. Our home inspection said it was 1.5 ton, but I guess he was just guessing. That's good to know...I was thinking 1.5 ton was undersized for our home and it should be 2 ton.

    After I manually defrost the coils I get a 20F rise out of the registers (over indoor temp) when it's about 35F outside. After a few hours that drops to about 10F rise (measuring 20 mins after auto defrost so compressor has been running for 20 mins). System works great when it doesn't have to defrost.

    I'm thinking that Goodman wouldn't design SmartShift so that it doesn't properly defrost, so there must be some other problem. A more experienced tech (the one who installed the new air handler) is coming to look at it, so I'll let him figure it out. I think he turned the SmartShift to reduce noise when he installed the compressor blanket for us, so he'll have a better idea if the sensor is in the right position.

    The capillaries from the metering device frost up within 10 mins of starting after I completely defrost the coils, and there is also light frost banding on the coils after 10 mins. Not sure if that has any bearing. This is with 97% humidity and 38F outdoor temp.

    Also, it does seem to be working fine (normal heat register temps) after the first auto defrost...I think it's just gradually losing performance when it frosts up more and more. So main issue is just not defrosting (which may be due to a restriction or being low on charge).

  8. #34
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    Aug 2009
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    Beatrice, NE
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    At 38 I wouldn't think it would have to defrost much. Also at 10 minutes run time it should be pretty well stabilized which would minimize any banding with correct charge/flow.

  9. #35
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    Jan 2020
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    Quote Originally Posted by BNME8EZ View Post
    At 38 I wouldn't think it would have to defrost much. Also at 10 minutes run time it should be pretty well stabilized which would minimize any banding with correct charge/flow.
    Well there isn't much frost after 10 mins...just a very thin layer (< 1mm), enough for the capillaries and the bands on the coils to have a white sheen. Seems to take about 20 mins for temperature at heat registers to reach peak after a defrost cycle.

  10. #36
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    Jan 2020
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    Looking inside, I can see that the banding is starting from the capilliary tubes coming out of the metering device. The capillaries are all heavily iced up and the defrost cycle doesn't remove the frost. The feeder tube (where I think the defrost termination temperature sensor is located) only frosts up a little bit and the defrost cycle removes that frost.

    So, am I correct in thinking that if everything is working normally it shouldn't be icing up from the capillaries? Given that the temp sensor is on the opposite end of the coil, I'm guessing that the lowest temperature should normally be where the vapor exits the evaporator coil, and if it's icing up at the capilliaries it means the pressure is too low going into the coil due to low charge or restriction. Does that sound about right?

  11. #37
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    Aug 2002
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    Southold, NY
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    Quote Originally Posted by cpncrunch View Post
    Looking inside, I can see that the banding is starting from the capilliary tubes coming out of the metering device. The capillaries are all heavily iced up and the defrost cycle doesn't remove the frost. The feeder tube (where I think the defrost termination temperature sensor is located) only frosts up a little bit and the defrost cycle removes that frost.

    So, am I correct in thinking that if everything is working normally it shouldn't be icing up from the capillaries? Given that the temp sensor is on the opposite end of the coil, I'm guessing that the lowest temperature should normally be where the vapor exits the evaporator coil, and if it's icing up at the capilliaries it means the pressure is too low going into the coil due to low charge or restriction. Does that sound about right?
    That’s the beginning g of absorbing heat so the beginning of frosting!

  12. #38
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    Jan 2020
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    Quote Originally Posted by pecmsg View Post
    That’s the beginning g of absorbing heat so the beginning of frosting!
    So why is the defrost termination sensor on the other end of the coil, or have I got that wrong? Bear in mind, I only have a rudimentary understanding of how heat pumps work, so I'm probably misunderstanding something here. I know the liquid absorbs heat and evaporates which takes heat away from the coil, but I don't know which end of the coil ends up the coldest.

  13. #39
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    Aug 2002
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    Quote Originally Posted by cpncrunch View Post
    So why is the defrost termination sensor on the other end of the coil, or have I got that wrong? Bear in mind, I only have a rudimentary understanding of how heat pumps work, so I'm probably misunderstanding something here. I know the liquid absorbs heat and evaporates which takes heat away from the coil, but I don't know which end of the coil ends up the coldest.
    Not going to get into the whole Thermo Dynamics involve in it!

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