Transportation and Vehicle Safety: question about car equipments, clutch mechanism, economy changes

Question
Hello, i am not sure my question is relevant but I'll give it a try anyways.

I have an used Corolla , my fist car so there are a few things i am really not sure, I hope you can help me out.

I understand that using the A/C will put more load on the engine. But how about the "fan", is it purely electric ( drain from battery ?) , how about the "temp knob". As far as I know , without turning on the A/C, I can still get Cold air from the vents if I set temp knob to COLD. How it works ?
How about the "Air circulate" button, does it work from battery ?

How the fuel economy changes if I set the temp to HEAT , to COLD.
Another question, Can I utilize the HEAT without turning on the engine ? Like SLEEPING IN THE CAR AT NIGHT !!
Do it reduce fuel economy if I use the temp knob to COLD/HEAT and fan ?

Thanks a million times !

Answer
Hello Brian and welcome to AllExperts!

Relevance is based solely on a desire to learn something. If it is important to you, it is relevant for us.

You are correct concerning a typical A/C unit whose pump is belt driven. When you operate the unit, a clutch mechanism engages the A/C pump which uses energy from the engine to power it. As there is greater load upon the engine to operate the A/C pump, your gas mileage will suffer.

There were a few vehicles whose A/C pumps were operated by an electrically driven motor, receiving their power from the alternator. In this case, no load was placed upon the engine for A/C, however, they had larger alternators to power the A/C pumps, and therefore a greater load was placed upon the engine all the time.

As to your question regarding the operation of a fan or any other electrically operated device within the car, just the like above paragraph, they all receive their power from the alternator. The alternator generates DC power and operates all the time whenever the engine is running. Regardless of what is turned on or off, no greater or less load is placed upon the engine.

Turning on the fan or operation of the temperature selector has no effect with the operation of the A/C, which has its own selector.

If the outside air is cooler than the air inside of the car, operating the cold/hot selector in the cool mode will make a difference in the interior temperature, but this is not a function of the A/C, rather it is allowing the colder air outside to replace the warmer air inside.

Also, operation of the selector in the hot mode will also change the interior temperature, but in this case, the outside air is being drawn through the hot engine and again, this is not a function of the A/C.

Lastly, nothing that uses electrical power will work without either the engine running or drawing from battery power. The hot/cold selector is a gate that determines where the air is coming from, but requires a fan to push the airflow. So, if you are sleeping in your car and need warm air or A/C, the engine must be running. If you just want air to circulate within the car or to draw outside air into the car, you can also use battery power, but within a couple hours, you will have a dead battery.

BTW... I would recommend that you not sleep in a car with the engine running due to possible exhaust leaks that are poisonous.

I hope this has answered your question Brian!

Have a great day!

Terry