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  1. #1

    air handler fan keeps turning on and off

    New homeowner with an older gas forced air/central a/c system. Had the a/c serviced at the beginning of the season, was in generally good condition for its age, the system was charged.

    When using the a/c the air handler would often run when the system was off, either set to cool but below the set temperature, or with the thermostat set to off. The fan was always set to auto. The tech who did the original servicing said it shouldn't be a problem as long as it continued to cool, and it did.

    Now I have the opposite problem. The a/c is running and the copper lines going into the air handler are cold, but the fan doesn't run all the time. I set the thermostat to off, and left the fan on auto, and it is now coming on for 15-30 seconds at a time then turning off again for about 2 minutes. This happens even when the fan is switched from auto to on.

    I'll be calling the tech again in the morning, but was wondering if anybody had any insights into my problem...

    thanks...



  2. #2
    Join Date
    Apr 2004
    Location
    Palmdale, CA
    Posts
    199
    What kind of thermostat do you have? Some are programmable to have the fan come on by itself. That is only a guess. May have to bite the bullet and get a tech other than this guy. How hot is it? Where is your unit located? I have seen fan limit switches set too low and the fan comes on when it reaches a certain temp if it is in a hot attic or garage. Just ideas. Wouldn't know without going there to look. But I am a rookie only been a tech for 3 years. Maybe one of these guys can give you better input to give the tech when he comes out.

  3. #3
    Originally posted by gcastillo
    What kind of thermostat do you have? Some are programmable to have the fan come on by itself. That is only a guess. May have to bite the bullet and get a tech other than this guy. How hot is it? Where is your unit located? I have seen fan limit switches set too low and the fan comes on when it reaches a certain temp if it is in a hot attic or garage. Just ideas. Wouldn't know without going there to look. But I am a rookie only been a tech for 3 years. Maybe one of these guys can give you better input to give the tech when he comes out.
    Its a digital thermostat. It is set to off right now and the fan is switched from auto to on. I replaced the thermostat earlier and got the same result.

    It is 81 inside right now, the unit is in the basement, but it is probably only 75 or so down here.

  4. #4

    identical problem

    Steve,

    What was the answer? I have the same problem. I don't believe the compressor is the cause. It continues to run, but the air handler fan shuts off intermittantly for 45 seconds or so. This happens even when in HEAT mode and when the fan is switched to ON as opposed to AUTO. I replaced the thermostat and that accomplished nothing. The air handler is in the basement which is considerably cooler than the rest of the house. I'm surprised no one can give us an answer! What would make the fan cycle on and off?

  5. #5
    Join Date
    Apr 2004
    Location
    Palmdale, CA
    Posts
    199
    Have a service tech come out and look at it. From the sounds of it he got it fixed when the tech came out. Very possible you have a bad blower motor.

  6. #6
    Join Date
    Mar 2005
    Location
    Louisiana
    Posts
    211
    Being it's an old unit check to see if the blower motor and the squirrel cage isn't so filty that it causes the motor to not turn at the correct RPM, that's where I'd check first.
    Is there good air flow coming from the register? and does the register appear to be dirty or black?, if filty then might at as well check the "A" coil too.
    Happy Findings

  7. #7
    I'll take the shop vac to it and see if that helps. Thanks.

  8. #8
    Tech says the motor is overheating and needs to be replaced. It's a York model furnace with a 1 HP motor.

  9. #9
    The problem was never resolved. After leaving the system to cycle for a few hours, the blower stayed on (with the thermostat in the on position), I then turned the a/c back on and put everything in auto and it ran ok. The blower still came on when the a/c was off, but it always ran when the a/c did. We just got back from vacation and when I turned the system back on, its cycling on and off again. This time the blower runs for 5-10 seconds, then off for exactly 4 minutes. Its been doing this for awhile now with the thermostat in the 'on' position and the a/c off. It also does this when the heat is on.

    Its an Armstrong furnace, about 20 years old. It has a new filter and good airflow through the ducts when its actually running.

  10. #10
    Sounds similar to my problem. The "off" cycle was always 1 minute and the "on" was erratic. My unit is only 7 years old. I'm putting the replacement blower motor in today.

  11. #11
    Had a tech come out today. He said electrically everything checks out, its switching when it should, the thermostat is working correctly, the motor is fine. He said the relay was hot to the touch though and there might be a short that may be tripping an overload, so they're replacing the relay later on today or tomorrow. But he's not exactly sure if that's what the problem is.

    I'll fill you in if its finally resolved.


  12. #12
    Join Date
    Jul 2004
    Location
    Southern Alabama
    Posts
    448
    I can't see how everything "checks out electrically."

    Is the motor contactor cycling with the blower? If it is then it is external to the blower. If the contactor is staying enrgized (which I doubt), then voltages and current draws on the motor can tell him if it is overloaded.

    If the blower is cycling with the tech there and he says everything is fine, get another tech to check it out.

  13. #13
    Join Date
    Jan 2004
    Location
    Lancaster PA
    Posts
    68,120
    Did it do it while the tech was there?

    If it did, and he can't find the cause, and just wants to start replacing parts, then you want another tech.
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