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  1. #1

    A/C freezing up?

    A few nights ago I noticed that when I turned down my upstairs thermostat below the current temp, it did not click and I never felt air blowing out of the registers.

    The next day I had someone out and he checked the freon which was good, and then we went into the attic to look at the unit there.

    It had been off for about 6 hours and when I turned it on, water began coming out of the unit (Comfortmaker N8MPN/L) into the pan.

    We ran the heat for 30 minutes, then switched to air and cold air began blowing forcefully out of the registers.

    The HVAC service tech said that it had frozen up and that since the freon levels were good and the filters were good that it was likely one of two problems...

    1. The thermostat was failing and leaving the compressor on even when the fan was not running.

    2. The electronic board in the actual unit was failing.

    It happened again last night. I turned it off and left it off, thinking that I would start by getting a new thermostat. I was hoping for one with a remote control so I could adjust temps from the bed without getting up at night - but Lowes does not have such a thing.

    I can pay $80+ for touch screen and various programability - but I didn't see any remote controls.

    My current thermostat is programable, but it doesn't keep time for squat so I've never bothered. That isn't an issue for me really.

    My questions are as follows...

    1. Do you think the advice that I was given is accurate and should I start with replacing the thermostat before calling the HVAC service person back out? That would be a relatively inexpensive and easy cure if it is a likely cause.

    2. Is there anything special you'd recommend in a thermostat?

    3. Anything that I'm not asking that I should?

    Thanks,

    -TS

  2. #2
    Join Date
    Feb 2008
    Posts
    1,275
    Why did you run the heat for 30 minutes? Was it still frozen when you went up into the attic? You can't check the charge if the evaporator is an ice cube. Was your house already cold and you were adding a heat load?

  3. #3
    Join Date
    Aug 2003
    Location
    Fort Worth, TX
    Posts
    11,369
    Is this a heat pump, electric heat, or gas furnace system?

    Always best to de-ice or defrost an a/c coil naturally vs. running heat pump in heat mode or turning furnace on (the latter method will likely pop the high limit switch and stress the heat exchanger). Best way to de-ice/defrost a coil is to switch the indoor blower control at the thermostat to "on" and let the blower run and run.

    Sometimes it can be tricky to find out what caused a system to ice up, but the most probably causes are dirty air filters, more than one supply register or vent in the house closed off, blocked return grills (someone moved a piece of furniture in front of it, etc.), dirty evap coils and blower wheels, restrictive ductwork that could be supply or return ducting...or both.

    I think your technician could've snooped around a bit more and perhaps found a more definite reason vs. possibilities. If your compressor was running all the time even when there was no call from the thermostat, seems you would've heard it by now, unless your outdoor unit is quiet and in an out of the way location.

    The most crucial thing to check whenever icing or frosting of an a/c cooling coil is a problem is AIRFLOW. The refrigerant charge can't even be checked correctly if airflow is not correct. In your case, your opening sentence could be a clue:

    A few nights ago I noticed that when I turned down my upstairs thermostat below the current temp, it did not click and I never felt air blowing out of the registers.
    No click could mean the indoor blower relay did not engage. Will the blower run if you switch the control on the thermostat to "on" vs. "auto"?

  4. #4
    Quote Originally Posted by Frostie View Post
    Why did you run the heat for 30 minutes? Was it still frozen when you went up into the attic? You can't check the charge if the evaporator is an ice cube. Was your house already cold and you were adding a heat load?
    Thanks for the response. I ran the heat because the service tech that was at the house said it would take "forever" if we just waited for the ice to melt and that running the heat would melt it faster.

    When we went into the attic and turned it (the a/c) on, water poured out of the side of the upper part of the unit and into the drain pan. However, airflow from the vents was maybe 1/3 or 1/4 of normal.

    After running the heat for 30 minutes, and then switching to A/C, the air was full force coming from the vents.

    I am NOT an HVAC expert so I can only tell you my understanding of the situation based on what the service tech said. My understanding was that the coils inside the unit had frozen solid, which was not allowing the airflow from the fan (which was on and blowing - pulling around 6-7 amps) to get past the coils and into the ductwork. I imagined a fan blowing towards a solid block of ice.

    My impression was that by turning on the heater, we would melt the ice and then we would be able to see if the A/C worked with properly by seeing if there was forceful, cool air coming out of the vents. Which we did experience and the A/C worked fine for several days after that.

    I should point out that I am in South Carolina and we have experienced mild temps recently. As such, I don't even know how often the air has actually come on to cool things down and how often it just stays around the 70 degree mark that I usually keep the house.

    Please let me know if I have left out any important information. Thank you for taking the time to offer your help.

    -TS
    Last edited by tsteele93; 04-07-2008 at 04:32 PM.

  5. #5
    Quote Originally Posted by shophound View Post
    Is this a heat pump, electric heat, or gas furnace system?
    Hi, thanks for the response. I have a gas furnace for my heat.

    Always best to de-ice or defrost an a/c coil naturally vs. running heat pump in heat mode or turning furnace on (the latter method will likely pop the high limit switch and stress the heat exchanger). Best way to de-ice/defrost a coil is to switch the indoor blower control at the thermostat to "on" and let the blower run and run.
    I will definitely do that in the future. I would like to point out that we have had mild temperatures here in SC and that we are looking at 40's at night and 65 in the daytime.

    That means the attic gets fairly cool at night and only warms up significantly in the day if there is bright sun.

    However, the house can warm up a good bit more due to insulation, people, cooking, etc... and as a result I do have the a/c running at least for a little while at bedtime if temps creep up past the 70 degree mark we usually keep the upstairs set to. Sometimes we will even kick it down to 69 a/c to cool things off just as we go to bed.

    Sometimes it can be tricky to find out what caused a system to ice up, but the most probably causes are dirty air filters, more than one supply register or vent in the house closed off, blocked return grills (someone moved a piece of furniture in front of it, etc.), dirty evap coils and blower wheels, restrictive ductwork that could be supply or return ducting...or both.
    I'll try to cover as much of that as possible. The filters are both clean and my tech has advised me to use cheap fiberglass filters rather than the pollen-filtering design as he says this puts more load on the system - and last Summer we had 105F days on end and the a/c was working hard to keep up, so I was taking any incremental improvement I could get. No one in my house has overt dust allergies, so we use the basic filters. And they are clean.

    He did not check the coils in the attic.

    No registers are closed off or covered to the best of my knowledge. All of our registers are in the ceilings, not floors. So that should be a fairly safe bet. Unless a critter has crawled up and died in there - but I don't smell anything.

    We did not check the ducting for any collapses. I can go up and do that today.

    I think your technician could've snooped around a bit more and perhaps found a more definite reason vs. possibilities. If your compressor was running all the time even when there was no call from the thermostat, seems you would've heard it by now, unless your outdoor unit is quiet and in an out of the way location.
    It is on the far side of the house from where we spend most of the time, so it could have been running and I would not know.

    The most crucial thing to check whenever icing or frosting of an a/c cooling coil is a problem is AIRFLOW. The refrigerant charge can't even be checked correctly if airflow is not correct. In your case, your opening sentence could be a clue:

    No click could mean the indoor blower relay did not engage. Will the blower run if you switch the control on the thermostat to "on" vs. "auto"?
    That is the question he asked me. And unfortunately these events have both happened late at night when sleep was my main concern. I woke up hot (well, relatively for me) and pressed the down button on the thermostat and expected to hear the click as the relay switched and did not. I checked the register and felt no airflow.

    At that point, afraid I might hurt it by leaving it on - I just turned it off, cranked up the ceiling fan and got rid of some covers.

    Right this instant it is working fine. I came in after having it off for 14-16 hours, turned on the a/c to auto, set it a degree cooler than the temperature in the house and it is blowing forceful cool air out of the registers.

    I really do appreciate all of the help you are offering. Please let me know if there is anything I am not communicating that you need to know.

    -TS

  6. #6
    Join Date
    May 2007
    Location
    Naples, Fl
    Posts
    889
    Have the servicer return; make a proper diagnosis then make the repair and guarantee the work.

  7. #7
    Join Date
    Aug 2003
    Location
    Fort Worth, TX
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    11,369
    It's possible the compressor didn't turn off after one of those cycles. Without being there I can't verify if you have good airflow or not. Airflow remains the primary cause for a system to freeze up, but a compressor left running with nothing else going will do it, also.

    I would not go changing the thermostat for the moment, unless you're just disgusted with the thermostat you have and needed a nudge to get a new one.

    A question...when the system iced up, was this the first time you had run the a/c since last cooling season?

  8. #8
    Quote Originally Posted by shophound View Post
    It's possible the compressor didn't turn off after one of those cycles. Without being there I can't verify if you have good airflow or not. Airflow remains the primary cause for a system to freeze up, but a compressor left running with nothing else going will do it, also.
    I just ran the system for a while and then turned up the thermostat so that it would automatically shut off. Then I went outside to verify that the compressor was off. It was.

    My concern is that it might not be turning off EVERY time.

    I will go up and check for any obvious signs of dirty coils in the attic later this evening when it cools down a little - plus I've got a kid napping (i.e. a kid taking a nap - not a felony crime) in the room below the a/c and don't want to wake him right now.

    I would not go changing the thermostat for the moment, unless you're just disgusted with the thermostat you have and needed a nudge to get a new one.
    Well, if they make one that has a remote I'd do it. But nothing at Lowes made me think, "I gotta have that thermostat." The one I have now is ok, it is digital and supposedly programmable, except that it doesn't keep time to save its life - never has. But it has always worked ok.

    A question...when the system iced up, was this the first time you had run the a/c since last cooling season?
    No, but we did take a week vacation and I left the systems both on HEAT at 63 degrees F to make sure the house didn't freeze up if we had a cold spell. When we got home we went back to normal operation.

    But I probably use the a/c 10 months a year here in Greenville SC - we get warm days in January sometimes.

    Thanks again for talking through this with me. I'll check the coils in the attic and get back on later tonight hopefully.

    -Tom Steele
    Last edited by tsteele93; 04-07-2008 at 05:26 PM.

  9. #9
    Quote Originally Posted by adrianf View Post
    Have the servicer return; make a proper diagnosis then make the repair and guarantee the work.
    I will do this if I can't get it sorted out here. To be fair to him, he has done me some big favors before (like replacing a fan on the outside compressor while I was out of town so it would be working when I got back and not charging me for it) and he refused payment when he came out the other day to look at it.

    His take was basically that since I turned it off when the problem happened, that it would probably be hard to chase down until it happened again. He told me not to do anything the next time it happened so he could see it in action. Unfortunately, that wasn't an option this time because I have company and today was supposed to be warm. So when it happened last night, I turned it off and let it sit so we would have a/c today.

    Next time it happens I will follow his instructions and have him come out and inspect it in full failure mode.

    I was just checking here to see if there might be a simple fix that could avoid a "next time."

    Thanks!

    -Tom Steele

  10. #10
    Join Date
    Dec 2007
    Location
    Ohio
    Posts
    2,876
    Please don't take this the wrong way but it seems to me that your HVAC guy is a hack.

    1. - Refridgerant charge CANNOT be verified with ANY amount of ice on the indoor coil.

    2. - Refridgerant charge CANNOT be verified until your blower speeds are set up properly using the blower chart and a static pressure reading. (or other methods)

    3. - Once your blower is set up properly and filters are clean and all registers are clear and flowing properly, you can move on to verifying refridgerant.

    4. - Refirdgerant needs to be verified by using superheat and/or subcooling....I would guess that your tech doesn't know what these are since he tried to check the charge with a frozen coil.

    5. - There are two reasons for frozen coils....either you have a serious airflow problem or you are low on charge...however you MUST verify them BOTH to be sure things are right, not just one.


    My advise to you would be to call someone else...I realize this guy has treated you pretty well (still trying to figure out the free compressor thing) but it doesn't really sound like he knows what he is doing. This is an issue that I and many, many other techs on this site would have diagnosed in less than an hour of testing. Once we made your repair many of us would guarantee our work as well. The last thing I want to do is see ANY of my customers more than once a season! That's not because I hate customers....just hate call-backs. But this is just my 2 cents worth.
    I need a new signature.....

  11. #11
    Quote Originally Posted by I_bend_metal View Post
    Please don't take this the wrong way but it seems to me that your HVAC guy is a hack.

    1. - Refridgerant charge CANNOT be verified with ANY amount of ice on the indoor coil.

    2. - Refridgerant charge CANNOT be verified until your blower speeds are set up properly using the blower chart and a static pressure reading. (or other methods)

    3. - Once your blower is set up properly and filters are clean and all registers are clear and flowing properly, you can move on to verifying refridgerant.

    4. - Refirdgerant needs to be verified by using superheat and/or subcooling....I would guess that your tech doesn't know what these are since he tried to check the charge with a frozen coil.

    5. - There are two reasons for frozen coils....either you have a serious airflow problem or you are low on charge...however you MUST verify them BOTH to be sure things are right, not just one.


    My advise to you would be to call someone else...I realize this guy has treated you pretty well (still trying to figure out the free compressor thing) but it doesn't really sound like he knows what he is doing. This is an issue that I and many, many other techs on this site would have diagnosed in less than an hour of testing. Once we made your repair many of us would guarantee our work as well. The last thing I want to do is see ANY of my customers more than once a season! That's not because I hate customers....just hate call-backs. But this is just my 2 cents worth.
    No offense taken. That is why I am here. Sadly, my experience with HVAC repair is that most of the time someone comes out, tells me they are charging the system and then they charge me - and it works for a while.

    Recently I had problems with the outside compressor and this guy helped me out. He came out the day I called (this was during 105 heat when everyone was on a three or four day backlog) and he helped me get the fan fixed on the compressor.

    Just to answer the curiousity of fixing the fan for free - he is a friend of a friend and did that as a favor. I'm sure the mutual friend called in a card or something.

    Anyway, I'm not defending or criticizing him - I'm just looking to figure out what is going on.

    It sounds like maybe I should try yet another HVAC repair person. Which would lead me to the next question...

    How do I find an HVAC repair person that is likely to know their stuff? Is there a certification I should look for?

    Thanks for everyone's help. I am trying to learn and solve my problem and I appreciate all the advice.

    -Tom Steele

  12. #12
    Join Date
    Mar 2004
    Location
    Illinois
    Posts
    6,959
    This thread amazes me...waaaaaaaaaay past the point of diy...

    Call a reputable service company, any qualified technician could diagnose this in an hour or two. As an added bonus to yourself look for NATE or RSES certifications.

    >>>Thread Closed<<<

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