In September, we discussed why you should keep your original factory A/C system. But what if it’s not working?
One common issue is that a fan doesn’t reach full capacity, yet all other speeds work. Most people assume the fan switch is bad, but in reality, the cause is usually a bad blower relay. The switch doesn’t control the high speed, it controls the relay which then activates high speed.
While fan switches can eventually fail, typically they never do on their own. If a fan switch does burn out (due to a loose terminal, there are burn marks on its back, or loses any speed other than high) it’s typically the result of a deteriorating blower motor which is drawing high amperage (or a bad ground connection to the motor).
The same is the case with resistors and relays. If a resistor has a coil burn out or any terminals loose, it’s likely the blower motor. Replacing any of those components without changing or repairing the blower motor may fix the issue temporarily. However, this will only cause the newly installed parts to fail again.
So before you order any new parts for a fan that does not reach high speed, remember to check the blower motor and connections first.