Car AC and Heaters

February 14, 2018

From the desk of Tony Muglia, Automotive Technology Department Head:

Have you ever been driving on a cool morning or a cold winter’s day and looked at the car next to you only to see that all the windows are fogged up on the inside? Then you may have started to wonder why this happens or maybe you are having this problem, too.

This is going to be one of the cheapest and easiest things to repair and the most overlooked thing by technicians. Here at Oklahoma Technician College, our students learn that the AC gets coolest when you can re-circulate the air inside the car. The heater/defroster only works when you can have fresh air coming in the car and that’s the big secret to defrosting windows.

There are 2 types of dashboard controls. Most domestic cars have Max AC and Normal AC on the controls. Most imported cars have a separate lever or buttons that say Fresh andRecirc. This is where all the problems start from.  On cars that have Max AC on the AC control heads, the difference is the fresh air intake door closes only in the Max AC position. Therefore, you don’t see the fogging up of windows on these types of cars because when you are in the heat or defrost position, the fresh air intake door is already open allowing the fresh air to come in.

foggy car window

Now, where most of these problems come from is on the cars that have the separate lever/ button that allow the air flow to re-circulate inside the car or come from the outside. When the lever or buttons are in the recirculation mode, the air is re-circulated inside the car only and does not draw in any fresh air from the outside. Therefore, the heater and defroster do not work as well and you cannot get the moisture out of the car. In the fresh air position, the air comes from outside the car and the heater works again.

So remember if you want the coolest AC then put the lever/button in recirc and if you want the best heat or defrost the lever/button needs to be in the fresh air mode.  The best part is that you can fix your problems with the AC/heater and it won’t cost you a thing.

Here’s another thing to consider if you are one of those people that likes to drives your car with snow all over it, looking like a tent with a peep hole. The fresh air to make the heater work comes from right below the windshield. So if that is covered with snow or ice you may not be able to get any heat or defroster to work in your car.  So till next time have a great day from here in the tool box!

Quote of the day: If you’re tired of playing with tinker toys, come see us here at Oklahoma Technical College and we’ll show you how to play with engine blocks and a whole lot more.        

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