I have a 2009 FIT bought used when i turn on the heater like vent or floor it works normally but when i put it on front defrost it sounds like the air conditioner compressor comes on and wondering if it`s normal. I bought the car in late spring and have used the ac so i know what it sounds like but only now using the heater for first time.

 

Yes, it's common in cars now that when you turn on defrost it turns on the A/C to help dehumidify. If it bothers you there are threads here about which wire to cut to turn that feature off.