[exploded99]

Warm her up, turn on the heat. Now go under the hood to where the two heater hoses go into the firewall. One of these hoses will have the heater control valve in it, a few inches away.

Put your hand on the heater hose, engine side of the control valve. It should be very hot - more than you want to hang on to. Now put your hand on the firewall side of the hose, behind the valve.

If its cool, the control valve is not opening. Pull the vacuum line off the valve. If there is good vacuum, the valve is bad. If there is no vacuum, you have a vacuum leak you need to find. That vacuum line goes back to the switch in the dash. There is a another vacuum hose which supplies vacuum from the intake manifold which also goes to the switch - its harder to trace along.

If the hose on the back side of the control valve is hot, then feel the other hose which is the heater core outlet. If it is hot, you have heat going thru the heater core - then you should suspect an electrical issue - temperature knob, etc.

If the other hose is cool, but the hose on the back side of the control valve is hot, you have a plugged heater core problem.

Suspect heater control valve first, vacuum second, heater core/electrical last.

Hope I made that clear enough!