I have a 15 year old FHP geothermal heat pump, the compressor won't start. In heat mode there is a slight humming, and every 30 seconds or so louder buzzing noise for a few seconds. The compressor is getting 220V to the contacts, the resistance between the then is in the range of 3 to 7 amps. I tested the start capacitor with a simple DMM using a resistance and volt modes, seems to work as it should. Any ideas? Time for a new heat pump? Should I try a new start capacitor anyway?