Home Diagnosis and TroubleshootingClimate Control and Air Conditioning Why Is It Hot On One Side And Cold On The Other: AC Problems

Why Is It Hot On One Side And Cold On The Other: AC Problems

by Jordan Harris
Why Is It Hot On One Side And Cold On The Other

I’ve been there before; wanting to crank up the AC on a really hot summer day, but instead, I find that it is blowing hot on one side, while the air conditioning is blowing out cold on the other, so why is this so?

When your car’s AC is not blowing out air at the right temperature that you’ve set it to, it’s typically a sign that your car’s air conditioning system is low on refrigerant, or if the AC unit’s blend door is faulty.

Otherwise, a bad heater core might also cause this issue, or it might also be caused by a broken blend door actuator (aka the ‘flapper door’). Even a poorly done airbag recall might also cause this problem, too.

Why Is My Car Blowing Hot Air On One Side And Cold On The Other

If your car’s air conditioning unit is blowing hot air on one side and cold on the other side, there are normally 5 common causes and reasons why this is so, which I’ll be explaining more in detail down below…

(Click on these to skip ahead to the relevant sections):

Besides discussing each of the aforementioned reasons why your car’s AC is blowing hot air on one side and cold on the other side, I’ll also discuss how these can be fixed and get your AC up and running again.

Reason #1: Blend Door Issues

Why Is It Hot On One Side And Cold On The Other

Your car’s blend door acts as the gatekeeper inside the HVAC system. Its primary function is to regulate the flow of air that’s either heated by the heater core or cooled by the AC evaporator.

This ensures that the air blown into the cabin reaches the temperature set by the driver or passengers. If your blend door is malfunctioning, it can lead to uneven temperatures on different sides of the car.

This might be due to the door being stuck, broken, or not receiving the correct signals from your AC unit’s control system. The temperature inconsistency is more pronounced when trying to adjust the settings.

FIX: Inspect the blend door for any visible damages. Use diagnostic tools to check if the control system is sending the correct signals to the blend door. If it’s stuck or broken, consider replacing it.

Reason #2: Low Refrigerant

Why Is It Hot On One Side And Cold On The Other

Refrigerant is the substance responsible for the cooling effect in the AC system. If your AC system is low on refrigerant (which is otherwise known as ‘Freon’ – and it needs a top-up), it can’t cool the air effectively.

An uneven cooling effect on your AC evaporator can result in one side of the car getting cooler air than the other. Another common symptom of this issue is noticing that your AC may take longer to cool the car.

Or, there’s a noticeable temperature difference between the center AC vents on your dashboard as well as the center console. The cooling effect of your car’s AC unit is furthermore less efficient than usual.

FIX: Use a refrigerant gauge to check the current levels. If your Freon levels are low, you can recharge the system with the right type and amount of refrigerant. Or better still, send it to a qualified technician.

Reason #3: Faulty Heater Core

Why Is It Hot On One Side And Cold On The Other

Your car’s heater core acts like a small radiator, using your engine’s hot coolant to warm up the air before it’s blown into the cabin through the AC. If it’s clogged or malfunctioning, it can lead to uneven heating.

The consequence of a faulty heater core might mean that one side (like the driver’s side) gets the initial hot airflow. Meanwhile, the other side (such as the passenger side, in this example) gets the residual, cooler flow.

The most common symptom of a bad heater core is noticing that your car doesn’t warm up evenly. So, one side of the AC unit might feel toasty while the other remains cold, especially during colder months.

FIX: If you suspect that the heater core is clogged, consider flushing it to remove any obstructions. This can restore the heater core’s functionality and ensure even heating across the air conditioning unit.

Reason #4: Flapper Door Issues

Why Is It Hot On One Side And Cold On The Other

The flapper door (aka the ‘blend door actuator’), similar to the blend door, is used to control the direction of the airflow within your car’s air conditioning system. Therefore, it’s a crucial part of the AC unit.

If the flapper door is malfunctioning due to a bad motor, obstruction, or maybe other issues, it can lead to improper mixing of hot and cold air. Thus, your AC blows hot air on one side, and cold air on the other.

FIX: Check the flapper door (blend door actuator) and all the associated components for any obstructions or malfunctions. Ensure that the stepper motor, which controls the door, is functioning correctly.

Reason #5: Airbag Recall and Dashboard Removal

Why Is It Hot On One Side And Cold On The Other

This is a bit unconventional, but if your car has undergone an airbag recall or repair, the dashboard might have been removed during the repair process, which is typical of any airbag-related servicing or repairs.

If your dashboard hasn’t been reattached properly, it can affect the AC’s ducts and performance. The best way to tell is if your AC may not feel as efficient as before the recall. Or, if there are other heating and cooling issues.

FIX: Disassembling your car’s entire dashboard isn’t something that I’d recommend for most folks to do. So, for this, I’d highly recommend that you consult with a professional mechanic or automotive AC specialist.

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