Heater blowes cold air

If memory serves the cap is on one end of the radiator with the tank to the lower hose not the upper. Unless the system is lowered or drained slightly you won't see flow thru the tubes, remember the lower hose is pulling coolant from the bottom. Second is these were notorious for popping the clips off the ends of the control cables. Look up under the dash somewhere just left of the glove box and see if the cable ends are still held in place, move the lever and you should be able to see the mechanism that opens and closes the temp door moving, if all that is well then it may have broken the door rod which lets the door flop around not hooked to anything. If that happened the heater box will have to come out, WOOOW. Good luck.