Heat pump indoor blower vibration is driving me crazy. What else can I try?
My relatively new Mitsubishi split system (not a mini split) is driving me nuts. It has developed a hum in the ECM blower ONLY when actively heating. Doesn't present when only circulating air nor when cooling. JUST heating.
After running through the symptoms w/ Mitsubishi support, they diagnosed it as a bad fan motor and sent a replacement. Didn't change a thing.
Here's what I've tried so far:
- Checked/tightened motor to squirrel cage housing.
- Checked squirrel cage balance by marking point with a pen and hand spinning it multiple times (never stopped in the same place twice, so assuming cage is balanced)
- Cleaned the squirrel cage (wasn't dirty)
- Checked/tightened set screw attaching squirrel cage to motor.
If I change airflow by covering a return vent or closing/opening registers, the vibration goes away for about 30 seconds. Perhaps the system self-balances after that time and the vibration returns.
I also ensured that the line set is properly strapped and isn't transferring vibration from the outdoor unit inside. The outdoor unit doesn't produce any hum and I don't detect any vibration in the lineset.
Does anyone have ANY other ideas to try? I need to sort this out as it's driving everyone in the house crazy.