Symptoms of a Bad or Faulty Blower Motor Relay

Symptoms of a Bad or Faulty Blower Motor Relay

The blower motor relay is an electrical switch used to power a vehicle's blower motor. The blower motor is the component responsible for delivering air to the vents of the vehicle's heating and air conditioning systems. Without it, the AC system cannot circulate heated or cooled air. The blower motor relay controls the current used to power the blower motor and is subject to constant on/off switching. Over time, it eventually wears out. When the blower motor relay starts to fail, the vehicle usually displays several symptoms that alert the driver to a potential problem that should be serviced.

The blower motor is powered by a fused-like device called a relay. If your heater or air conditioner won't blow through the ducts, this could indicate that the blower motor fuse may be blowing. Although it is simple to replace, the exact location of the blower motor fuse may vary from vehicle to vehicle.

1. blower motor not working

One of the first symptoms of a blower motor relay problem is a blower motor that does not work at all. Since the relay is the switch that supplies current to the blower motor, if there is an internal fault, the power will be cut off from the blower motor circuit, causing the motor to stop working or blow air out of the vent.


One of the first symptoms of a bad or faulty AC blower motor relay is an AC blower motor relay circuit fuse. If the blower motor relay develops a problem that interferes with its ability to properly limit and distribute power, the blower motor fuse may break. Excessive current from an electrical spike or bad relay of any kind will cut power to disconnect the fuse and protect the system.


Another serious symptom of a blower motor relay problem is a burned or melted relay. Relays are exposed to high current loads and can get hot if problems occur. In critical cases, the relay may even damage the fuse box and panels, as the internal parts of the relay and the plastic housing begin to melt and burn out.
The blower motor relay is essentially a switch that directly controls the power to the blower motor, so if the relay fails, the entire AC system will not be able to distribute cooled or heated air. For this reason, if you suspect a problem with the blower motor relay, have a Vermin-Club expert technician diagnose your vehicle's AC system. They can determine if the blower motor relay needs replacement or another repair in the car to return full functionality to your AC system.

How do you test a blower motor relay?

If so, try to start the motor and see if the relay picks up when the motor is first started. If it picks up and the motor doesn’t start, it could be the contact isn’t making it. Quickly turn it off before it destroys itself sitting there on the locked rotor... Put a continuity test on the contact to see if it closes when it is picked up.

If the relay doesn’t pick up, quickly turn the motor off. See if there’s a starting capacitor on the motor... It should be in series with the starting relay contact. If so, capacitive reactance = 1000,000 over 2pi F C, where F = frequency and C = capacity in microfarads... This will give you the capacitive reactance of the capacitor in ohms. Now ohm's law... I = E over X sub-C... (Capacitive reactance). Use 120 volts for E in the formula as well as the voltage when testing.

What are the signs of a bad blower motor relay?

Simply jumper the terminals in the relay’s socket with power applied. If the blower turns on, the relay is bad. If it doesn’t, either the motor, its grounding, or the feed from power to the motor is bad.

What can cause a blower motor relay to go bad?

When a relay opens, the magnetic field holding it shut collapses. This collapsing field generates a large voltage spike (1000v) in a direction to slow the opening of the relay and thus prolong the arcing between the contacts.

The arc damages the contacts (and can even weld them shut!). There are many solutions to this. One is to provide components to limit the voltage rise and shorten the opening time.