I had a problem like that where one of my legs (wires) was dropping down to around 70 volts instead of 120. Turned out that the meter socket had gone bad and had a poor connection, and it was a contributing factor in killing my heat pump. I had an electrician buddy pull the permits, have the power company disconnect service line at the transformer located at the telephone pole, he installed the new meter box, and then had everything turned back on. After that I replaced the heat pump since it was well past its lifespan. For his work, it just cost me my time to help him rebuild a motor.

The first step is you should call Dominion, they are responsible for the step-down transformer at the pole and line going into your meter box, and if you're lucky the problem will be on their end. If it's your meter socket, or breaker panel, you're going to need an electrician. Be warned though: HVAC equipment is very sensitive with low voltage and can be damaged when attempting to run with it. And most of the other electronics, like TV's and computers don't like low voltage either.

Good luck...