The process of pumping down a heat pump is quite simple. First you should switch the unit into air conditioning and put your compound gauge on the suction line. Make sure the unit is running. Then...
Normally an AC unit does not have a vacuum pump in it. It does have a compressor - but the vac pump is a tool for installation. Once you have an air tight network of pipes connecting the indoor and...
An AC unit isn't supposed to heat! If you mean a heat pump, then you may have a relay switch problem. Or maybe, your thermostat is in the cooling mode. Contact a repairman.