HVAC is not my specialty, but I would think you are probably low on coolant. With the engine off and cold, check the coolant level. Refill it as necessary. Warm it up and see if it improves.
If it is low, that means that you have a leak somewhere. What you would do is borrow a cooling system pressure tester from AutoZone, Advance Auto, or O'reilly Auto Parts and hook it up to your radiator. Pump it to 15 lbs and go look for a leak. Here is a more in-depth description of what to do:
https://www.2carpros.com/articles/radiator-pressure-test
Let us know what you find.
Friday, March 23rd, 2018 AT 3:43 AM