Why is there hot air coming from my vents all the time?

You replaced the entire HVAC (climate control) sytem

Assuming you have a dual climate control system, the blend door actuator for the passenger side has stopped working and would need to be replaced

warmth comes from the heater in the car
if it is climate control check the climate control module
check for heater control in the vent settings as the hot water tap may not be turning on

the heater core is removable from the climate control unit. The climate contriol unit has to be removed to replace it. The A/C system must be evacuated and lines removed as well as the dash, to access the climate control unit. The steam is coming from a leaking heater core.

You likely have a faulty blend door. It could be electrically, mechanically related, or even a broken door. It may be the blend door motor, or possibly the temp sensor.

Joey i had a similar problem in my 2000...The problem lies in the A/C Actuator. The Actuator is what opens and closes the vents, when the vents are open it allows hot air to flow through and when thier closed it prevents hot air coming in while air conditioner is running. depending on the year some vehicles require an upper and lower actuator. they are fairly simple to replace, and dont take much time. most actuators are located under the control switch box (radio, a/c dials) parts run about 60.00 each.

your Escalade has dual climate control, it sounds like one of the blend door actuators is stuck.sometimes when they stick you may even hear a clicking noise. the actuator has small plastic gears that strip out.

If your climate control isn't set to "vent" then your blower valve (on the heater core) is stuck, and should be cleaned/replaced.

it is the flap door inside the heater box area.alot of gm with electronic climate control have the problem.there is an actuator motor that needs to be replaced.

Have you had the A/C system charged .. you may be out of refrigerant