I have a 91 honda accord?

No heat out of vents all controls work fan blowing. Hose going into heater core hot but one coming out cold. I'm thinking it's bad but wanted some other thoughts on this before I tear into it.

Usually that is a sign of the heater control valve sticking shut. You will see it right beside the firewall, under the hood, with an operating cable. If it is off (lever perpendicular to the hose) you can rotate it to the on position (like pushing with the cable) with water pump pliers or by hand if you have a strong hand.

If the valve is jammed it can be left open but must eventually be replaced. To replace it, cut the hose from the valve to the heater core and peel the remains off the soft brass pipe from the core… Do not mash or distort the pipe. To reset the cable on the new valve, remove the passenger side panel on the center console. The mechanism is below the radio. The Haynes manual has decent pictures and instructions.