4 reasons the AC only works when driving and stops while parked

At times it’s frustrating when the air conditioning only works while the car is moving and doesn’t when parked, especially when the atmospheric conditions are hostile to you.

Often, it’s a minor issue that you can quickly fix, especially if you’re a hands-on person when it comes to vehicles.

This post will highlight some of these issues. Hopefully, I might save you a needless visit to the mechanic that could be overly expensive.

Let’s dig into it!

The AC only works when your car is moving: Top 4 reasons explained and the solutions

Note: The problem is sometimes caused by the combination of more than 1 factor.

4 reasons the car ac only works while driving but doesn't blow cold air when parked.
When the AC doesn’t work while parked but only blows cold air while driving, the causes may come from stuck condenser fans, low refrigerant level, stuck compressor clutch, and/or dirty compressor.

1. The condenser fans don’t come on automatically

Condense fans are responsible for transferring the heat from the refrigerant system into the outdoor air. After leaving the condenser, the refrigerant moves to the orifice tube or expansion valve and then the evaporator coil. So, the purpose of the condenser fans is to reduce the temperature of the refrigerant so it can condense.

They are designed to rotate when the engine reaches its optimal operating temperature, about 195°F to 220°F. This function is made possible using the engine temperature switch that monitors the engine’s temperature.

When failure occurs, proceed by checking the relays and fuses of the condenser fan. Additionally, troubleshoot the wiring to the vehicles for corroded or loose connections, short and opens circuits. The instances that reflect that the fan socket is getting adequate current indicate that the fan is dead.

A couple of reasons might kill the fan, including a faulty temperature switch, defective coolant sensor, or perhaps the engine thermostat might be stuck OPEN, meaning that it never gets hot enough to trigger the fan. Furthermore, a faulty fan control module and a dysfunctional fan motor might be the cause of all your turmoil.

car ac condenser fan
AC condenser fans are designed to rotate when the engine reaches its optimal operating temperature, about 195°F to 220°F

The easiest and fastest way to troubleshoot issues related to the fan circuit is to crank the engine and switch the AC to MAX. A rotating fan indicates that the fan motor and the wiring, including the fuses and relays, are perfect. However, the test provides insufficient information to rule out issues related to the temperature sensor and PCM.

If you’re having doubts about the temperature sensor, check its resistance using a multimeter. Furthermore, the multimeter can help you check for blown fuses, bad relays and check continuity in the wiring to your fan.

Jumper cables are your saving grace when it comes to troubleshooting the fan motor. You can rule out this issue by unplugging the wiring connections to the fan and using jumper cables from the battery to direct power to the fan. A functional fan motor will run flawlessly at average speed. Contrarily, a faulty fan motor will run slower than expected even after being supplied with 12V of power.

Replace the faulty components, including the sensors, thermostat, relays, and fuses, to return the vehicle’s AC functioning to normalcy. For the fan motor, you can get a replacement or have it rebuilt by a trusted mechanic. Wiring issues can be corrected by tightening bolts and nuts to prevent loose connections. Additionally, pouring a water mixture with baking soda into the corroded wires will remove the corrosion.

Read more: Want to read the OBD2 codes related to your AC system? My recommendation is to buy an OBD2 code reader. A cheap Bluetooth scan tool such as Bluedriver is an excellent fit.

2. Low refrigerant charge

Vehicle manufacturers use a low-pressure switch to prevent the compressor from running if the system is low on refrigerant. Moreover, AC compressors will require a constant oil supply to prevent catastrophic failure.

To troubleshoot errors denoting to low refrigerant charge, follow these guidelines:

  • Crank the engine, roll down all the windows, and switch on the AC.
  • While the engine idles, with the blower speed set at 2, allow a minimum of ten minutes for the engine to reach its optimal operating temperatures.
  • Study the AC pipe in the engine compartment for moisture and note the temperature. The pipe should feel cold and condensed water visible over it.
  • Check the same pipe near the firewall. If you notice that it’s cooler, then there is a possibility of low gas volume.
low ac refrigerant level
Your vehicle uses a low-pressure switch to prevent the compressor from running if the refrigerant is low.

Mechanics use a two-dial pressure gauge to determine the gas volume of your refrigerant. The device is connected to the high pressure (HP) and low pressure (LP) lines to take the readings. It’s a relatively easy task that you can accomplish by yourself. Refilling the depleted refrigerant will be the way to go.

If the issue is only about low evaporator pressure, the better solution is recharging it through the low-pressure port while the compressor is still engaged. DIY recharging kits are used in this scenario. However, low refrigerant levels will result in the clutch never engaging.

You should note that it’s bad practice to hotwire the low-pressure switch to force the compressor clutch to engage while you recharge as you may be running the compressor with little to no oil. It might accept the charge, but it will cost you the compressor.

Recharge the freon in your AC if you know the procedure. Otherwise, it is preferable to seek professional help.

ZeroR EZ Chill R134a freon refrigerant

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Rating

AC Pro Car AC R134Afreon refrigerant

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Chemours Freon R134afreon refrigerant

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[Video] How to recharge the freonrefrigerant in your car AC:

How to recharge your car’s AC system

3. The compressor clutch is not cycling

The compressor clutch is responsible for engaging the compressor shaft. If it fails, the air conditioning compressor can’t pump refrigerant. 

To determine whether the compressor clutch works, turn the AC to MAX and crank the engine. The pulley and the clutch should spin in unison at this stage. There is a severe fault with the system when only the pulley is rotating. The clutch might fail to engage because of several reasons. 

The compressor clutch is responsible for engaging the compressor shaft. If it fails, the air conditioning compressor can’t pump refrigerant. 

An open circuit resulting from broken wire to the clutch coil, blown fuses, a fault clutch coil, or poor ground might be the cause. It could also be a low-pressure lockout that is causing all the trouble. All in all, use a multimeter to narrow down the faulty components.

Replace the faulty component to resume the regular running of your car. You can eliminate issues about loose connections by tightening the respective nuts and bolts. You can handle grounding issues by revising the wiring, thus correcting the error resulting from the live wire’s contact with the earth wire. 

Read more: Do I need to add oil when recharging my car’s AC compressor?

4. The compressor might be blocked or dirty

The compressor is tasked with circulating the refrigerant between the evaporator and the condenser coils.

You can identify leakages by performing a visual check on the AC line, condenser, and compressor. You will notice accumulated dust that results from sedimentation of oil around the leaking lines. Ensure that you check the AC filter as it might be clogged due to dust accumulation.

dirty car ac compressor
A dirty compressor may be one of the causes for the problems.

Using a pressure washer, wash the condenser through the openings in the bumper. Suppose you notice muddy water dripping down; it means that the compressor is clogged. Be cautious not to point the washer jet over the condenser as it’s susceptible to damage. Instead, spread it out. Perhaps it would be a better option if you took your vehicle to a washing center and have them wash the radiator carefully for you. Your car AC will resume normal functioning after this.

Bonus: Want to know the OBD2 codes related to your AC system? Search AC system OBD2 codes here

Why the AC only works when the car is moving?

Conclusion

Fan, compressor clutch, and low refrigerant charge issues are identified by cranking the engine and setting the AC to MAX. Check if the fan is running, and note whether the clutch is rotating with the pulley.

Most problems related to the air conditioning system are wiring-based. Issues such as blown fuses, faulty temperature and coolant sensors, dysfunctional thermostats, defective relays, short and open circuits are easy to identify using a multimeter.

Moreover, a visual test can help you detect corroded wires. Have the faulty components replaced or remove the corrosion from the wires using a solution of baking soda and water.

Read More: How Long Can I Drive with a Misfiring Cylinder?

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