the car was moving but not at idle. Or worse yet, you come out to start the car one day, turn on the AC and it’s blowing barely cold air when it was fine just yesterday. What happened?
How Car AC Works
The AC in your car works in the exact same fashion as your AC at home or your refrigerator. Both systems circulate refrigerant through a closed circuit, compressing it to a liquid state and then evaporating it to provide cooling. Both systems include a compressor, condenser, evaporator, and receiver/drier. Your refrigerator, however, isn’t subjected to the extremes of heat and vibration that go on under a car hood. The system in your car has several failure points—O-rings, seals, rubberized lines—all of which can crack, dry out, and shrink, leading to a loss of refrigerant. Car AC designs are far more robust than they once were, but even a late-model vehicle can lose as much as 10 percent of its refrigerant over a year’s time.
Why is your Car AC Blowing Hot Air?
In most cases, it’s due to a loss of refrigerant in the system. Your car AC is actually a heat exchanger that recirculates warm air from inside the cabin and replaces it with cold air. What happens is this: Refrigerant that’s in a liquid state makes its way to the evaporator, where it “boils” as warm air from the cabin flows across it. When the system is low on refrigerant, though, this liquid refrigerant lingers in the evaporator and is exposed to more hot air from the cabin. The refrigerant near the exit of the evaporator is superheated, but the moisture in the refrigerant entering this component starts to form ice crystals, freezing up the system. Sometimes, freeze-ups can occur due to poor air circulation through the condenser. The condenser is located near your radiator and looks like a smaller version of the radiator, with loops of coils and fins that disperse heat and allow the refrigerant to return to a liquid state. Since it’s right up front with the radiator, it’s easy for the condenser to pick up bugs, leaves, plastic bags, and other trash and debris from the road. Free Car AC Diagnostic Near Me
How To Diagnose Your Car’s AC Problem?
3 Common AC Problems
- COOL BUT NOT COLD.
- AC Compressor.
1. AC Cool But Not Cold?
If the air conditioning is set to max cool and fans on high but is only blowing moderately cool air:
- Check to see that the cooling fans on the condenser or radiator are running when the air conditioning is on.
- Look for any restrictions like leaves, bugs or dirt that would keep air from passing over the condenser.
- Check the cabin air filter to ensure that it is not clogged.
Check the pressures in the system using a manifold gauge set. The recommended high-side and low-side pressures can be found in the repair manual.
2. AC Compressor
Speaking of the compressor—your A/C compressor clutch is one of the most important parts of a vehicle’s air conditioning system. It pressurizes the A/C system and keeps the refrigerant flowing so that everything works properly. 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 regulate the flow of refrigerant in the A/C system to deliver the cool air you crave. When diagnosing an air conditioning issue, it’s easiest to begin at the compressor:
- With the engine running turn the A/C on max cool, set fans high, and make sure that the clutch is engaging on the compressor. Note: this is not the pulley, but the centerpiece that engages the pulley to the compressor shaft. If the clutch is engaging and disengaging rapidly, the refrigerant may be low.
- If the clutch is not engaging, use a voltmeter to check for voltage getting to the compressor.
- If there is voltage – the clutch may be bad.
If there is no voltage – a cycling switch may be bad, a fuse may be blown, and the system may not have enough refrigerant pressure to trip the low-pressure cutoff switch that cycles the compressor.
3. Car AC System Leaks
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. Leaks are the most common problem associated with the air conditioning system. If the pressure is low, then there may be a leak:
- Using a UV A/C leak detection kit is the easiest way to find a leak. Follow the instructions on the packaging to introduce UV dye to the system and UV light to find the leak.
- Check around all fittings to verify that they are all secure.
- Check hose manifolds on the compressor.
- Check the front seal and the o-rings sealing the pressure switches on the back of some compressors.
- Check where the hoses are crimped onto the fittings.
- Check the Schrader Valves.
- Check for pinholes in the condenser.
- Check where the evaporator drains condensation with UV light. Sometimes oil or dye can be seen.
Note: The dye check will not work if the system is too low and the compressor is not cycling.
Car AC 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 distributes the proper amount of refrigerant to your 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 starts 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.
Car AC 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 will 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. Free Car AC Diagnostic Near Me
Car AC 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 uncover what’s plaguing your car air conditioner. Schedule an appointment online or stop by your nearest location today!
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