Heater question...

[xtreme80]

My 80 C10 has factory air and heat, and the AC blows cold, and it blows hard out the vents, but when I turn on the heater, it won't even trickle out unless I'm moving. I can turn the selector to heat or off and it still blows out the hot air, but just barely.

Is there a relay somewhere that allows the fan to kick on when you have "heater" selected on the unit? Is it the same relay as the regular AC relay? I know there's one for the AC that has like 6 or 7 wires coming off it. Is this the same relay?

Sheesh, I need a wiring diagram if anyone's got it.

Thanks!