HAVING PROBLEMS WITH HEATER. OWNER BEFORE ME SAID HE REPLACED HEATER CORE. A/C WORKS BUT DONT BLOW THROUGH VENTS LIKE IT SHOULD . HEATER BLOWS COLD OR WHAT EVER TEMP. IT IS OUTSIDE.

Heater core isn't getting water circulating through it from the system or else it would adjust to whatever temp you want.Could be blockage to heater core. Does your heater core gurgle at all? When your heat level is on high is there warm water in the hose going to the heater core? I'd check the thermostat or if you even have one. Also when was the last time the whole system was reverse flushed and refilled?