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New blower fan installed

last month
last modified: last month

I replaced my furnace blower fan. its std 1/3 hp, 1075 rpm. i have an OLD furnace. it does not have a switch for lo/med/hi and you have to wire motor manually. the old blower was replaced during heating season so perhaps it was wired to med speed? my ac has always struggled and basically ran 24/7. Ok, it did shut off sometimes from midnight to 7am. now the thermostat actually cycles it on/off. who knew?

Comments (4)

  • last month

    So, what is your question?

  • last month
    last modified: last month

    If i only increase airflow why does my system perform better? i have same compressor condenser and evap coil.

  • last month
    last modified: last month

    I would surmise that replacing the blower fan has resulted in higher air flow and that before the replacement the air flow was too low.

    "my ac has always struggled and basically ran 24/7"

    "If i only increase airflow why does my system perform better?"

    Answer from Copilot Ai:

    If the blower in a split‑system air conditioner runs too slowly, the entire refrigeration cycle is pushed outside its design envelope. The immediate effect is insufficient airflow across the evaporator coil, and from there a cascade of predictable failures follows.

    Core takeaway

    A too‑slow blower causes the evaporator coil to get too cold, leading to icing, poor cooling, high humidity, longer runtimes, and potential compressor damage.

    What actually happens inside the system

    1. Evaporator coil temperature drops → frost and ice formation

    Low airflow means the coil cannot shed heat fast enough. Air lingers on the coil surface, refrigerant absorbs less heat, and coil temperature falls below 32°F.

    • Ice begins at the distributor or lower rows
    • Frost expands and chokes airflow further
    • Eventually the system enters a runaway freeze‑up condition

    2. Humidity removal increases briefly, then collapses

    Initially, slow airflow increases latent removal because the coil is colder. But once the coil starts icing, moisture can no longer reach the coil surface.

    • Indoor humidity rises
    • Supply air becomes cold but clammy

    3. Temperature distribution becomes uneven

    With reduced CFM, conditioned air cannot travel through the duct system at proper velocity.

    • Rooms far from the air handler get little airflow
    • Hot/cold spots appear

    4. Compressor runs with abnormal suction pressure

    Low airflow → low evaporator pressure → high compression ratio. This increases:

    • Compressor amp draw
    • Discharge temperature
    • Long‑term wear

    5. System may short‑cycle on safety limits

    If airflow is too low, the coil can freeze or the heat exchanger (in heat mode) can overheat. Either condition triggers limit switches that shut the system down prematurely.

    Why manufacturers specify minimum airflow

    Residential systems are designed around roughly 350–450 CFM per ton. Below that range, the coil simply cannot operate in a stable thermodynamic state.

    Summary

    A slow blower in a split system AC is not a minor comfort issue — it destabilizes the refrigeration cycle. The consequences include coil icing, humidity problems, uneven cooling, higher energy use, and potential compressor damage.

  • last month

    When you replace the motor did you you clean the squirrel cage blower? That may of done it.