Ok first, you need to make sure that coolant is actually circulating through through the heater core. Just feel the hoses.. They should both be warm, or hot to the touch. Also, the obvious.. is the engine warmng up? Most likely....?? If not, then put a thermostat in it.
Anyways, back to the heater hoses...
It they don't get hot, then look for a shutoff valve on one of the hoses, or a low coolant level. If all of that is good, then the heater coer is clogged.
Here is a picture of where they are under the hood:
If BOTH hoses are getting hot, then there is a problem in the control panel or the actuator that moves from hot to cold air. The vent could also be stuck open You will need atleast some basic hand tools and a voltmeter to look into any of that.
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