I have an 18k mile 87 IROC. I just replaced the heater core, refilled it with antifreeze, and when I went to turn on the heater, found the lever is stuck on cold. I've owned the car for 2 years and never had a reason to move the lever to hot. Does anyone have ideas on what to check?

 

IIRC, the HVAC Control Head Temperature Lever is connected to a Cable that attaches to a Temperature-Door on the Case for the Heater-Core.

The door will cover the air that would go through the Heater-Core when the Cold Position is selected (Air can pass through the AC Evaporator Core).
In the Hot Position the Door will do the opposite in order to bring air through the Heater-Core for Hot air.

 

The Cable is probably frozen from lack of use.

 

That's what I'm thinking as well. If frozen, should my next attempt be to remove the hvac controls from the dash and lubricate to see if it will free up?

 

There really is not anything to lubricate...

Most of the time the braided steel Cable gets stuck in the black Sleeve of the Cable Assembly.
The Cable usually will need to be replaced.

 

try wiggling it with a pair of pliers at the lever under the dash were it connects to the heater box while another person tries to move it at the controls
don't force it though