Why Does My Car Air Conditioner Blow Cold Then Warm?

  • May 28,2018
Why Does My Car Air Conditioner Blow Cold Then Warm? Why Does My Car Air Conditioner Blow Cold Then Warm?

There’s nothing quite like cranking your car's air conditioning up on a hot summer day. Few things feel better than that cool blast of air! But what if your car air conditioner blows cold and then warm air? 

If it feels like your A/C is playing tricks on you and doesn't blow cold air for long, it could be time to bring your A/C problems to your local Firestone Complete Auto Care. Any number of culprits could be causing your car A/C to blow cold then warm air, including: 

A Leak in the A/C System

A small refrigerant leak is the most common reason a car's A/C gradually loses its cool. A leak is typically caused by a mixture of moisture and refrigerant that, when combined, creates a corrosive acid that eats away at seals, valves, and hoses in the A/C system. A leak in your A/C system could be causing the unit to blow warm air, since there isn't enough refrigerant in the system to cool things down. 

Even worse, the acid can corrode the inside of your compressor, spreading metal fragments throughout your A/C system and causing widespread damage, blockage, and component failure.

A Faulty Compressor Clutch

Your A/C compressor clutch is one of the most important parts of a vehicle's air conditioning system. It allows the pulley to engage and disengage from engine power so the compressor is only working when needed. Since it continuously cycles on and off, it's subject to wear and tear every time you use your A/C. 

When there's a problem with the compressor clutch, your air conditioner won't blow cool air for long. A damaged, failing, or worn compressor can't properly compress refrigerant in the A/C system to deliver the cool air you crave. 

A Failing Expansion Valve

If your A/C flip-flops from hot to cold and back again, your expansion valve could be failing. The expansion valve removes pressure from liquid refrigerant to allow expansion from a liquid to a vapor state in the evaporator. If the valve is blocked, the refrigerant flow could be restricted or could be too unrestricted. 

A slight restriction of refrigerant flow can cause that mechanical part/hardware to get very cold. So cold, in fact, that frost or ice can build on the outside of that part/hardware. A buildup of frost or ice can make the operation even worse inside the system. The result? Your A/C blows warm air. A large restriction of refrigerant will also result in your A/C blowing warm air. 

Contrary to what you might think, too much refrigerant flowing into the evaporator doesn't lead to cooler air. This is sometimes called a "flooded" evaporator, a problem that will also leave you with warm air. 

As the system continues to try to modulate the expansion valve or cycle the compressor, the flow rate of the refrigerant can normalize, which is when you might notice the air temperature start to cool again. 

Make note of puddles of water under your car – this could be a sign of a freezing problem and can help your technician diagnose the problem.

A Blown Fuse or Electrical Issue

Your car's A/C system is made up of a jungle of wires, switches, relays, and fuses. Under normal operating conditions, these pieces and parts work together to deliver power to the A/C unit, giving you cool air – on demand. 

If just one of these parts fails, your A/C could shut down and start blowing warm air. While this helps prevent dangerous electrical fires, it also means that a simple, single blown fuse could cause your entire A/C system to shut down. 

Help Us Diagnose Your Car's A/C Problem

Help our technicians diagnose the culprit that's causing your A/C to blow cold then warm by taking note of the following:

  • Are all of the vents getting warm, or just one?
  • How long were you driving before the A/C started blowing warm air?
  • Has this happened before and if so, how many times? Under what driving conditions?
  • Does the A/C start blowing warm air on the highway? In stop-and-go traffic?

When your car A/C blows cold then warm, head to your nearest Firestone Complete Auto Care. An A/C performance check is the easiest way to start uncovering what's plaguing your car air conditioner. Schedule an appointment online or stop by your nearest location today!

Up Next

Find Store

Find a Different Location

Stores Near You

Do you want to change your Preferred Store?