Informational Guide

AC Only Works When Car Is Moving (Causes & Solutions)

It can be confusing if the AC only works when the car is moving. Learn about all the causes and solutions for this problem.

by Josh M

It’s a hot summer day and you can’t get the car air conditioning to blow cold air unless you are driving; now what? What does it mean when the AC only works when the car is moving? In this guide, we discuss what to do when the air conditioner in a car only works when driving.

1. Defective Compressor Clutch

The clutch of the compressor is needed to engage the compressor itself. If it doesn’t work, the air conditioning can fail to run. This problem could be intermittent as the clutch is failing. To see if it is working, set your air conditioning on to the MAX setting.

At this point, the clutch and pulley would spin together if everything is working right. If not, you may only see the pulley rotating. Sometimes the fault stems from a broken wire coming from the clutch coil. It could also be due to a blown fuse, poor ground connection, or faulty clutch coil. It’s also possible that there’s a low-pressure lockout.

You can use a multimeter to narrow down the problem. Then, if you see a wiring issue, repair it and test the air conditioning again.

2. Faulty Condenser Fan

If the AC in a car only works when driving, it could be due to a problem with the condenser fan. This part is responsible for transferring the heat coming from the system and dispelling it into the atmosphere. It needs to reduce the temperature so the refrigerant can condense properly.

If failure occurs, you can check the fuses or relays to the condenser fan. You also need to look for loose or corroded wiring connections. Additionally, a malfunctioning coolant sensor, failing temperature switch and stuck OPEN engine thermostat can all lead to the condenser fan not working, so you must do a proper diagnosis before replacing any parts.

Related ArticleCar AC Condenser Cleaning Guide

3. Blocked Or Dirty Compressor Fan

If the fan isn’t broken, it’s possible that it is just dirty or blocked with debris. Because the compressor must circulate the refrigerant, any blockage would lead to problems, some of which could be intermittent.

To check the system, it’s best to start by looking at it. If you notice debris on the compressor, condenser or AC lines, you want to remove it. You can wash the condenser with a pressure washer through the bumper of your car. If you see muddy water pouring out, it could mean a clog. However, you don’t want to spray high-pressure water on the condenser, or you could damage it. Instead, spread the water flow out so it is evenly applied across a larger surface. Finally, retest the system to see if it is working now.

4. Low Refrigerant Charge

Why does AC only work when the car is moving? If there isn’t a constant supply of refrigerant in the system, it could work sporadically. To determine if the levels are low, you will need a two-dial pressure gauge showing you the volume in the system. Connect it to the low pressure (LP) and high pressure (HP) lines for an accurate reading.

You can purchase refrigerant refilling kits to get the levels back where they belong. To do the job yourself, you will save a lot of money. However, if you aren’t familiar with the procedure to recharge the Freon, you should seek help from an automotive professional.

Car Interior and AC Controls

AC Only Works When Driving: Cost Of Repair Estimates

If the air conditioner only works when driving, you could be looking at any number of repairs. Each of these comes with its own cost, some of which can be cheaper than others. If you can perform the work yourself, you might be looking at a much lower bill since a lot of the cost can be labor.

Here are a few averages to consider:

  • Cost to recharge car AC: $25 to $200
  • Cost to repair faulty wiring: $5 to $500
  • Cost to replace faulty condenser: $400 to $750
  • Cost to replace faulty compressor: $750 to $1,250

Make sure you get a proper diagnosis before you replace any expensive parts. You don’t want to throw money at the problem only to find out it didn’t fix it.

People Also Ask (FAQ)

So what do people usually want to know about car AC? Here are some of those questions

Why does my AC not work when idling?

The condenser might have gone bad, causing the system to struggle when processing Freon. The condenser could malfunction whenever power is cut back, such as when the car idles or is running on the battery.

Why does my car AC only work in the morning?

The air conditioning system chills the air about 25-30 degrees cooler than what’s entering the system. If the day gets warmer, the air might not be as cold as it was when you started the drive in the morning.

Should I turn off my AC if it is not cooling?

It’s unlikely that you will cause further damage if the system isn’t running right, but to be safe, you should turn it off. Plus, you don’t want to use more engine power than needed, as that just wastes fuel.

How long does a hot car take to cool down?

When the air conditioning is running properly, it should only take five to ten minutes to cool off the cabin. However, if you parked in direct sunlight, the temperatures could be higher than normal. According to the CDC, in just one hour of being parked in 80-degree weather, the car interior could reach 123 degrees.

Conclusion

Why does my car AC only work when driving? As discussed, there could be many issues leading to your trouble, which is why you must take the time and do an in-depth diagnosis of the system. Then, once you get the fault repaired, you can enjoy the open road with cooler inside temperatures again.

Last Updated on March 29, 2022

Josh M

My name is Josh and I am obsessed with the HVAC industry. I created this website to help HVAC techs of all levels get the best out of their heating & cooling systems. I have spent thousands of hours studying air conditioners, heaters and home air products so you can learn & buy with confidence. Learn more about the team here.

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