There will be no warm air if the heating water pipe does not pass through the heating water tank. Secondly, I can't imagine what it would be like if you connected the warm air outlet pipe with the warm air return pipe. If there is no warm air water tank to store water, the water tank will of course discharge excess water.
The heating pipes are connected together for recycling, so as to provide warm air when the car is cold and help defrost the windshield. The warm air pipe is the pipe connecting the water tank circulation system and the heater. Its function is: the engine starts, and the water temperature rises slowly for a large cycle. At the thermostat, the warm air pipe is directly connected to the small water tank of the heater. The small water tank has temperature, and then the temperature can be dissipated by the fan. The temperature is controlled by the sensor. There are also very luxurious cars and electric heating measures. Warm air can be carried out even when the water temperature is not up, and the installation position is wrong. Just connect the pipe to the small water tank of the heater.