If little air arebeis 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 arebeis stuck or broken.
The fan switch may arebeis 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 arebeis 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 arebeis replaced.