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  1. #1

    Air Handler Won't Stay On

    Hi Folks -

    I've got an air handler in the attic - "hydro air" unit for heat and AC. The unit is 10 years old. Robertshaw t-stat. Air handler is "First Co.". I am planning to call our service techs regarding the problem below, but before I do, I would love to get some insight on possible causes.

    Currently, when I turn the blower/fan on the t-stat to "on" (even if heat/cool setting is "off" - the fan would come on but then after a few minutes would TURN OFF. After sliding fan back to "auto" for a few minutes (say 5-10 mins) - I would try again and the blower would come back on. Sometimes it would stay on, sometimes it would turn off again. Normally, when the fan is set to "on" (not "auto") - it would run indefinitely.

    Now on a hot day in Mass. - I've got the AC on - and basically the same thing: I put t-stat to "cool" - and with fan on "auto", I click temp down until I hear it click to call for air. The blower comes on WITH condenser running (cool air) - but only for a few minutes as the fan then STOPS but CONDENSER KEEPS RUNNING (because air temp is not satisfied). If I click temp up to cease the call for air and let it stand for a few minutes, and then click back down to call for AC again, it usually comes back on - but again only for a few minutes (i.e., the cycle repeats in failure...)

    After letting everything sit "off" for a few hours - at the height of the day (presumably very hot in attic) - I again attempted to turn the AC on. This time - I heard the click to call for cool. I heard the condenser kick on and coolant pumping - but the fan did not come on at all. A few hours later in the evening, I tried again and the fan came on for a few minutes, but then shut off again.


    In short - all circuits seem to be calling/responding appropriately except blower FAN is not staying on when needed (even when set to "ON").

    Any insight greatly appreciated.

    Many thanks -
    Brad

  2. #2
    Join Date
    Feb 2011
    Location
    North East Ohio
    Posts
    741
    Sounds like a motor is over heating. I reccomend calling a pro in to find out WHY? Good luck

  3. #3
    Join Date
    Jul 2002
    Location
    SE Texas
    Posts
    435
    There is really nothing you can do that you haven't already done. When your service techs get there, tell them what you've posted here and they should be able to easily diagnose the issue and get you up and running in no time.
    With your chrome heart shining in the sun, long may you run.

  4. #4
    Join Date
    Jul 2006
    Location
    Virginia
    Posts
    4,512
    Have your credit card ready and call

  5. #5
    Thanks for the responses so far. As I said in the original post, I'm planning to call and I realize there will be a cost involved.

    What I'm trying to accomplish in this posting is to see if there are typical causes for the type of issue I'm describing. I'm not so sure about the motor overheating, as NCHeat suggested - as I did another experiment and found the following:

    - I've been told that the HEAT on my system works as follows: zone valve gets call for heat and fires boiler, pumps hot water over to air handler. There must be a t-stat in the air handler - when the air handler gets to a certain temp, this is what causes the fan to kick on. (I guess this is to avoid blowing cold air before enough heat is passing through the radiator - as well as to blow the residual heat out into the house after temp is reached so the heat doesn't just get wasted in the zone.)

    - So last night I tried turning the HEAT on - the fan ran and ran - didn't stop on its own before satisfying the called temp. Seemed to work fine with no issue of fan prematurely stopping.

    - However, after I let system sit for a bit - I turned cool/heat to "off" - put fan to "on" - and back to the problem: the fan only runs for about 5 minutes. Same thing when trying to run AC.

    So I assume the mechanism that kicks the fan on for AC is more direct - that is - when I turn AC "on" and set a min temp - the blower is supposed to come on immediately (and off when min temp is reached). I also assume this is the same mechanism that turns the fan on when I set the fan to "on". However - the mechanism for turning the fan on for HEAT appears to be something different - I assume the t-stat in the handler - and THAT seems to be working just fine.

    SO - logically - I'm thinking it's not so much a problem with the fan/blower itself, or the motor, etc. - but rather whatever the process is to kick fan on/off for AC or when setting fan to "on."

    I hope this makes sense. So a more direct question is: what are the types of parts that might cause failure turning the fan on as described above (for AC, or manual "on", but not for heat)?

    Many thanks -

  6. #6
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    66,764
    A bunch of possible parts. And most of us don't like taking a stab in the dark at only one or 2 possibilities, don't bet on the motor not being the problem either.
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