Check your thermostat. Probably stuck open.
Remove both heater hoses from inlet & outlet of heater core. Connect these hoses together.
The easiest way to check is to feel the heater hoses going into the firewall. Check the hoses from a cold start and check that both hoses get uncomfortably hot at about the same rate. This is a good indication that coolant is flowing.
Remove the hoses going to the heater core. Use a regular water hose with a high pressure nozzle and flush both ways.
In line on the heater hoses on the passenger side of the engine. Has a small vacuum line to it and both heater hoses go through it. The heater hoses are smaller than the radiator hoses and go through the firwall.
the heater core could be stopped up, or could be low of antifreeze, or the thermostat could be stuck open
Check both the heater core as well as the heater hoses for leaks...........
Disconnect both heater hoses from heater core and connect them together
Remove the hoses going to the heater core. Use a regular water hose with a high pressure nozzle and flush both ways.
I would disconnect both heater hoses from the engine, then fabricate a way to connect a garden hose to one of the hoses leading to the heater, then gently turn on water supply for a minute, then attach garden hose to opposite heater hose and flush again, then reattach both hoses to engine and top off coolant reservoir.
undo the hoses from the fire wall and poor coolent into both of the hoses until the coolent fills up and starts comng out the hoses at both ends
Take both heater hoses off at the heater and the hose running from the front, attach it to the rear of the engine.
Heater Control Valve IF there is Vaccume going 2 it.Butt feel both heater hoses & if the Valve is bad - only one hose will b HOT.