HVAC ? Evaporator Freezing Over

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  • 4651feeder

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    Two year old system consisting of Amana gas furnace and Bryant a/c with N coil. Since day one I have complained the blower appears anemic when compared to previous unit, dealer doesn't think that a valid complaint.

    The evap. first froze over last month, thinking the blower to be slow I called the service man out after confirming the blower is wired for the fastest of the four speeds available. He found system measurements within range and attributed the freeze over to a loose piece of insulation in the coil hood blocking airflow, sounded reasonable at the time. Fast forward to very little a/c use in between, today the evap. froze over again. Just before the first freeze over I had installed a DuPont Ultimate 9600 Allergen filter. Took it out after the problem today and have yet to have another freeze over yet (It's only been four hours). Have others found the above filter in like new condition to be too restrictive on other furnaces? If my blower is up to spec should it be able to function as designed with this filter?
     

    DocIndy

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    The allergen filters are a tight pleat to catch smaller particles. Anything that restricts airflow will lower the airflow across the coil. Lower airflow means a colder coil. That causes the condensate to freeze versus run out the drain. Not necessarily a refrigerant charge issue, but the TXV on will he cool could also be the cause. I've replaced several of n the last couple of years. There was also a service bulletin about an issue with h the compressor oil not playing well with TXVs due to a additive from the manufacturer. What are the model numbers from now he equipment?
     

    AGarbers

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    If the freeze starts at the metering device, such as an orfice or TXV, it may be low on refrigerant. If it is all over the evap, it's airflow, or lack there of. Make sure all the vents are open. Make sure nothing is blocking the return. If the duct is undersized, it will cause freezing. If the indoor coil is undersized when compared to the condenser, it can freeze. Make sure the fan is running the right direction, and that the blower is installed in the correct direction. You may try running the unit without the blower door in place to see if it stops freezing up. You'll have to tape the door safety switch closed (in). You may even need to unhook part of the supply ductwork to see if that cures it. If doing either cures it, it's ductwork sizing issue. You could have the installing contractor prove that it is getting the proper airflow by doing an air flow measurement at the outlet of the unit. If I remember correctly the rule of thumb is supposed to be 400 cfm per ton. Lastly, and evaporator defrost control could be installed. An EDC can be inserted into the coil itself, or strapped on a U-bend on the coil. The EDC would be wired to turn of the condenser if the evap started freezing and turn it back on once the coil warmed up. That's not an ideal cure, but it does work.
     

    4651feeder

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    Literature states it's a Bryant 113A(A,W)/116BNA with a CNPVP/CNPVT N coil setting on top an Amana AMH8 (Glorified Goodman).

    All along I've been going on a theory of reduced air flow across evap causing the icing, but found even with the filter changed out to a much less restrictive one it iced up again late last nite. Not sure blower is that anemic in my mind. Water drains just fine and everything else is clean inside the cabinet as it's only two years old. Guess I'll give the svc. guy a call shortly and see if his gauge readings give a different indication than they did last month?

    You know the 16 yr old York system never gave me this much issue before I preemptively replaced it in anticipation of my retirement. This wasn't/isn't supposed to happen...............
     

    GodFearinGunTotin

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    Is the motor a multispeed? A unit we had in our old house had different wiring configurations for the blower motor to be able to change the speeds. You said it felt anemic, if it's like that old one of mine, maybe they set it to the wrong speed. If so, it's easy to change. Often the connection diagrams are in the unit or your installation information.
     

    4651feeder

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    Took care of the blower speed settings last month.

    The way I read it on this furnace black is fastest (a/c), blue is next (high heat), orange follows (low heat), with red being the lowest (park). When I looked last month before they came out, both black and red were parked and the a/c was spliced into orange (low heat). I said WTF? before correcting that myself, then discussed that action with the service guy when he came out. I have had only one service complaint previous to May and that was the blower was noisey and anemic, apparently another service man believed that would correct that issue. I understand sometimes one does not want the highest speed depending on application to insure moisture in the air gets captured; but I believe running the a/c on this unit at the next to slowest setting was wrong.
     

    churchmouse

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    If you have a marginally sized return putting in a highly restrictive filter could result in reduced air flow and cause the freeze up.

    If the tech looked at the pressures with the filter in place this should have been obvious as the suction would have been low. Pulling the filter and pressure rises then that is the issue. If not then it is low on refrigerant.

    The insulation could have caused an issue as well but this would have shown on the gauges. Did he hook a set up and monitor the unit..???
     

    churchmouse

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    Took care of the blower speed settings last month.

    The way I read it on this furnace black is fastest (a/c), blue is next (high heat), orange follows (low heat), with red being the lowest (park). When I looked last month before they came out, both black and red were parked and the a/c was spliced into orange (low heat). I said WTF? before correcting that myself, then discussed that action with the service guy when he came out. I have had only one service complaint previous to May and that was the blower was noisey and anemic, apparently another service man believed that would correct that issue. I understand sometimes one does not want the highest speed depending on application to insure moisture in the air gets captured; but I believe running the a/c on this unit at the next to slowest setting was wrong.

    You need a minimum of 400 CFM of air flow per ton. High speed is usually the speed needed.
     

    ChristianPatriot

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    In May it had 135 psi suction, 375 psi liquid with 74º ambient air.

    I agree with Mouse that those are a high but there's a lot more info needed to make sense of those numbers. Superheat, subcooling, temp in the house. Typically the high side should correlate to 30 degrees above ambient and the low side should correlate to 30 below house temp.
     

    churchmouse

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    I agree with Mouse that those are a high but there's a lot more info needed to make sense of those numbers. Superheat, subcooling, temp in the house. Typically the high side should correlate to 30 degrees above ambient and the low side should correlate to 30 below house temp.

    Yup. Looking for a 40* coil if air flow is on point. That comes up 118.9 on the temp/press chart.
    74* ambient look at 105* condensing (Avg) and that equates to 339 PSI.

    If all else holds in spec it is a bit over charged. Could be a very short line set and the installers did not adjust the charge on start up.
    Could be an idiot charged it up from scratch and though "More is better"

    This will not cause icing. I would say the duct work is questionable as to sizing and the addition of the high impact filter put it into the red on air flow.

    Now, realize we are diagnosing over the internet.....:dunno:
     

    4651feeder

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    When he arrived today the outside temp was approaching 82º, house was 75º, initial pressure readings were low. He added 1.5# of R410 and went in search of the now apparent leak he was sure was not present in May. No leaks showed up inside, so he went back out and determined the schrader on the suction side had oil present. Replaced that schrader. When all was said and done the readings are now 129 psi suction, 298 psi liquid, 56 S/A temp, 75 R/A temp, 11 superheat, 4 subcool. I believe this line set is close to 10'. Hoping he's right about the leak source. As he explained it, he felt under the circumstances the only charge today should be for the 1.5# of R410. Is the going rate for that stuff around $84#/$128 total or were some labor charges hidden in the bill?

    Thank you all for your contributions, you've expanded my knowledge greatly.
     

    churchmouse

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    Did he look in the shrader valve caps and see if the gaskets were in place.
    There will always be oil on the shraders after you pull the gauges. Always. It is a given.

    When confronted with the leak you can never find pulling the gauges and replacing the caps will sometimes show the leak is a faulty cap/gasket.

    The shrader valve is the same piece used in a car tire or any tire/tube. It is a common piece not designed to hols 330 PSI on its own. There will always be some leakage through them.

    Glad you have this "Fixed" and hope it does not re-occur.
     
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