My outside unit (heat pump) is not running. I was troubleshooting with help from some of the guys here and I thought it was the capacitor. I just put in a new capacitor and it did not do anything. While I was there I saw that some of the lines going to the coil had a light frost on them. Is that an indication of low refrigerant? and if that is the case, will that cause the fan not to run while the compressor makes a humming noise?