Question: I hate the heat and I’ve been noticing that my car’s air conditioning system stops working when I’m stopped at a red light or if I’m idling. Why is the A/C only working and blowing cold air while I drive?
Answer: If your AC only produces cool air when your car is moving, then you might have a fault somewhere in your AC system. Let’s take a look at possible suspects.
Faulty AC condenser fan
A faulty AC condenser fan could explain why you get decent air conditioning while moving but nothing when you are stationary at a red light or while parked.
Here’s how it works in simple terms. Refrigerant in an AC system goes through the system, into the cabin of your vehicle, absorbs heat from the cabin, and then goes to the AC condenser in your engine bay to get cooled.
When you are driving, air that moves over the AC condenser provides the wind chill required to lower the temperature of the refrigerant. However, once you stop driving, you have to depend on the AC condenser fan to provide the wind chill. A broken AC condenser fan would cause poor heat dissipation, causing a stark contrast in performance of your AC when you’re in motion and when you’re stationary.
Low on refrigerant
The quantity of refrigerant is important because it acts as the medium for heat exchange. If your refrigerant is at required levels, you should have no problems getting cool air from your vents. However, if your refrigerant levels are low, and you notice that there’s a correlation between higher RPMs and air conditioning performance, then you should check whether you are low on refrigerant.
How this works is that as you increase your engine speed, the AC compressor has an easier time pumping more refrigerant through the system. However, at idle speeds, the anemic AC system might not be able to pump enough refrigerant through your system.
Blockage in condenser
While the AC system should be a sealed system where no debris or foreign objects should be able to enter, old systems can decay and allow foreign particles to permeate into the system. These clog the system, leading to a poorer flow of refrigerant through your AC.
When it’s normal for AC not to work while driving
There are also some circumstances where your AC wouldn’t produce cold air. Some modern cars have a start-stop function which shuts down the engine when you stop your car at red lights. In most cases, when the engine is off the AC does not run, only the blower fans do, which could be one reason. However, some vehicles with stop start technology have electrical AC systems, meaning they will continue to run when the engine is off.
Xuyun Zeng is a content strategist with a wide-ranging content background including tech, journalism, cars and health care. After graduating with highest honors in journalism, Xuyun led a newspaper to win eight awards, helped start an award-winning film industry podcast and has written over a hundred articles about cars repair, state laws and insurance. Prior to joining Jerry, Xuyun worked as a freelance SEO consultant with a mission to create the best content that will help readers and grow organic traffic.
Chris Burkhardt is a writer and editor with over a decade of experience across various storytelling mediums. With Jerry, Chris hopes to help anyone with a question about their vehicle easily find the answers they are looking for. Whether you need to know how much insurance costs for a classic car, how to replace a broken light or tell if you need an oil change, Chris wants to help you find solutions the best he can. Prior to joining Jerry, Chris was a digital content producer and writer for NBC and a freelance editor for NerdWallet. A graduate of the University of Oregon’s School of Journalism and Communication, if Chris is not working on content, he’s sure to be found cheering on his Ducks!
