The air-conditioning evaporator is a small radiator inside the dashboard that provides cold air for the air-conditioning system.
It’s called the evaporator because it’s where the freezing liquid refrigerant takes on any heat from the air blown through it and changes into a gaseous state (evaporating it) before returning it to the air-conditioning condenser to shed the heat; the process is constantly repeated.
The air that emerges from the air conditioner is cold as a result.
The evaporator is typically hidden inside the vehicle’s dashboard and can be labor-intensive to replace, which then requires a full system recharge.
Unlike a ruptured heater core, which can leak engine coolant into the foot wells, a leak in the evaporator releases only refrigerant vapor.
A clogged drainage channel is a common cause of water in the front foot wells.
A/C Condenser
The air-conditioning condenser is a radiator positioned between the car’s grille and the engine-cooling radiator in which the gaseous refrigerant sheds heat and returns to a liquid state.
The liquid refrigerant flows to the evaporator inside the dashboard, where it cools the cabin.
Not cool enough for you?
It might result from a clogged air-conditioning condenser or disabled cooling fan.
A leak in the condenser will also result in a loss of refrigerant.
Cabin Air Filter
The cabin air filter serves to clean the air drawn in by your car’s ventilation system.
A car may have multiple filters to achieve different objectives, such as to limit pollen or odors, to provide sequential filtering or just for “packaging” reasons: to provide enough filtering and airflow in a tight space.
Manufacturers commonly recommend filter replacement every one to two years, but it depends on the car, filter type and how dusty your environment is; check your owner’s manual for recommendations.
Odors, inadequate airflow and disproportionately loud fan noise are signs that the filter needs replacement.
Air Conditioning Diagnosis
Your air conditioning system is really part of a larger system, known as the HVAC (heating, ventilation and air-conditioning) system.
Your A/C system includes a condensor, evaporator and the cabin air filter.
A/C Compressor
The compressor is the power unit of the air-conditioning system that puts the refrigerant under high pressure before it pumps it into the condenser, where it changes from a gas to a liquid.
A fully functioning compressor is necessary for the air-conditioning system to provide peak performance.
On most cars, A/C compressors are driven by an engine-accessory belt.
If the belt is worn and slips, the compressor won’t operate at full strength.
Compressors can also leak refrigerant, resulting in less cold air going into the interior. Internal parts can also fail, leading to no cold air.
Not all air-conditioning problems are because the system is low on refrigerant. Some are caused by issues with system parts, such as the compressor.
A/C Recharge
When your air conditioner blows only mildly cool air or no cool air at all, it’s probably low on refrigerant, the gas that many people still refer to as “Freon” but which now is a different substance, R-134, that’s less damaging to the environment.
That means it’s probably time for an A/C recharge, but there’s more to it than just filling ’er up.
Because the refrigerant operates in a closed system, the most likely cause for low levels is a leak in the air-conditioning system.
The most common practice by repair shops is for a qualified technician to inspect the system for obvious leaks, such as in hoses, pipes or the air-conditioning compressor, and make repairs as necessary.
They would then extract the remaining refrigerant into recycling equipment that removes any impurities; recharge the system by injecting the “clean” refrigerant back into the system; and top it off with fresh refrigerant as needed.
Environmental Protection Agency (EPA) regulations forbid releasing refrigerant into the atmosphere, and specialized equipment is required to extract it.
That would be followed by a performance test of the system and running an electronic leak test.
Heater Blower Motor
The blower motor is the fan that pushes heated or cooled air through dashboard vents based on the climate system settings and the fan speed selected.
Adjusting the fan speed sends a signal through a resistor to the blower motor to either pick up the pace or slow it down.
The blower motor resistor adjusts the amount of current going to the blower motor based on the selected fan speed.
When a blower motor fails, only a small amount of air will come through the interior vents based on the amount of outside air entering the climate system.
Heater Blower Motor (Part 2)
If the fan doesn’t work, before pointing the finger at the blower motor, check fuses for the motor to make sure they’re still good.
Many vehicles have two fuses for the blower motor, one in the interior fuse block and the other under the hood.
The blower motor is usually under the dashboard on the passenger side.
Blower motors that make loud squeaks or rattling noises may be worn out and on the verge of packing it in, but sometimes those noises are caused by leaves or other debris that can be cleaned out after the motor is removed from the vehicle.
Heater Blower Motor Resistor
The heater blower motor reduces or increases the amount of air blowing through the dashboard vents based on the fan speed selected or, in an automatic climate control system, the interior temperature and other factors.
But resistors, small electronic parts tucked out of sight, are what actually control the fan speed by reducing the amount of electrical current going to the blower motor.
When everything is working properly, setting the fan speed at its lowest setting, for example, will tell the resistor to restrict the amount of current to a low level.
But if the resistor burns out or wears out from corrosion, there is nothing to reduce the amount of voltage going to the blower motor for the lowest fan speed, so it will most likely get the maximum current and run at full speed.
When a resistor fails, the fan will often run only at higher speeds or the highest speed, no matter what fan speed is selected. In some vehicles, though, the fan may not work at all, and only a little may come through the vents.
On many vehicles, the blower motor resistor, which comes as a module that connects to an electrical wire and is mounted near the blower motor, is accessible by removing the glove box or checking under the dashboard.
On others it’s behind the dashboard, and part of the dashboard may have to be disassembled to reach it.
Heater Blower Motor Resistor (Part 2)
If little air is coming through the vents (hot or cold), then it could be because the blower motor for the fan or a switch or resistor that controls fan speed isn’t working. Another cause might be that the electronically controlled “blend doors” that direct air flow are stuck or broken.
The fan switch may be at fault, but a more likely reason is that a blower motor resistor that controls the voltage going to the blower has packed it in, resulting in only one speed remaining operable – usually the highest speed.
When a blower resistor fails, the highest fan speed usually is the only one that still works because it essentially bypasses the resistor and receives the maximum amount of voltage. When the resistor is working, it reduces the amount of voltage going to the lower fan speeds so the fan runs slower.
Blower resistors are small parts that can become corroded or just burn out, and a new one often costs less than $50. Because they’re usually under the dashboard on the passenger’s side or behind the glove box, near the blower motor, they can be hard to reach if they need to be replaced.
