It sounds like you have air stuck inside the core, I would start the engine and allow it to get warm, then turn the heater on full hot and high fan speed, then jack the rear of the car up.
This guide can help:
This should push the air out of the system, you can also jack up the front of the car after the rear as well, the idea is to help the air purge from the heater core.
Please check out this guide as well:
Please go over these guides and report back.
Monday, February 20th, 2023 AT 11:18 AM