Should cold air return be running constantly?
You will hear air circulating in the cold air return (or return air grille) when the heater or air conditioner is running.
Food is best thawed in the refrigerator, however, some frozen foods can be safely thawed in a container of running cold water. This will reduce the defrosting time but it is important that the water be cold and running. For this method, the food should be tightly wrapped or frozen in a container so that it is not in direct contact with the water, the water must be constantly circulating around the food so that…
If your car running less then 10 minutes then it's considered a car with cold transmission fluid (fluid should be in the region of cold level marks, but not lower), if more then 10 minutes then it's hot (fluid should be in the region of hot level marks, but not higher). When you check transmission fluid level your car should be running.
Check your temperature gauge. If it shows the engine is running in the normal range then there could be a problem with the "air door" that controls how much air is brought in through the heater core. Or the core itself is plugged and needs to be flushed out. If the guage shows the engine is running cold , then you should have the thermostat replaced.