Hi,
That is odd. Do me a favor. When the engine is cold, loosen the return line (heater core hose at the firewall). With it lose, have a helper start the engine and see if you can get air to come out and then coolant. Since you have no heat, something is preventing the coolant from entering it.
I attached a pic below of the heater hoses at the firewall. If I recall correctly, the one on the right is the return.
Please keep in mind, this will get messy. LOL Protect your eyes and wear old clothes.
Joe
Image (Click to make bigger)
Wednesday, April 7th, 2021 AT 7:08 PM