I have a heat pump for my house's heating and cooling. We had our first hot day of the year last week, so I switched it to cool mode (heretofore it had always been in heat mode). When in cool mode, however, i have no air flow at my vents. The air handler is on (there's sound), but it's not as loud as it usually is. I think the fan isn't running. I opened the chamber where the air filter goes, and I didn't feel any airflow. Furthermore I see ice crystals forming on the refrigerant lines. In heat mode, everything works fine (the fan comes on, and there's plenty of airflow).

Is this a problem that I can diagnose/fix myself, or should I call an HVAC company to look at it? It's an old system I'm planning on replacing in the next year or so, so I'm hoping to not put a lot of money into fixing it if possible.

  • Does putting the thermostat system switch OFF and the thermostat fan switch ON (from AUTO) work? Commented May 21, 2020 at 22:58
  • Looks like setting the thermostat to FAN doesn't do anything. It's quiet
    – atanamir
    Commented May 21, 2020 at 23:39

1 Answer 1


Your blower motor's HIGH speed died

Most furnaces and split-system air handlers run their blower at a high speed in FAN and COOL, and at a lower speed in HEAT. As a result, it's possible for the blower to work when the system is set for one mode, but not the other. I would consult the manual for your existing air handler/furnace for instructions on changing the blower speed used during cooling and fan-only operation. This will change the latent/sensible balance during cooling, but will at least keep you running until you can get the blower, or the whole system, replaced.

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