The unit is an armstrong 17 seer less then a year old. Worked great all summer but as soon as we went to heat we would hear a loud humming noise from the outdoor unit when it started up and went into defrost. The installer came back out and initially thought the compressor was bad so he replaced it but it still made the same noise. After more research he found there is a delay jumber on the deforst board that is suppose to stop the compressor for 30 seconds when going in and out of defrost. He took the jumper out but it still makes the same noise.
I also tried placing the unit and cool and it made the same noise for a long time. It seems like whenever it switches between hot and cold eaither deforst or not it makes this noise. When it does into deforst i can hear the reversing valve go and the loud swoosh then the compressor makes the loud humming noise for like 10 to 30 seconds.
Right now the installer thinks there is a problem with the delay because it doesnt seem like the compressor is turning off. When it goes into deforst the fan is still spinning but he never seen this problem before and isnt really sure if thats the issue. I wanted to see what everyone here thought about it.