My air handler comes on on the heat cycle. The air coming from the vents is not warm. My condenser unit outside is not coming on. There is a slight humming sound , I don't know if the compressor is working or not , its very quiet for a big compressor. My electric bill was over 400 dollars last month. Help...

I think you would probably know by the noise if the compressor was running, what you probably hear is the contactor switch in the condenser.

I don't know where you live but your high bill could be because of very cold weather so cold that you Heat pump would not run because it was turned off by an outdoor thermostat and you heat strips were heating your home.

@letmetellu... The breaker was tripped. I flipped it back to "on" and the outside unit was working great. Do you think it is not going into "defrost mode" and causing it to tripp somehow? (oh it's a heatpump unit)

Havve you had a lot of snow where you live, if so it could be that the fan got loaded up with snow and could not turn therefore tripping the breaker. I would just wait and see what happens, it may not happen again./

Actually yes, about 12" of snow a week or so ago.

Thanks much!