A blower relay acts as an electrical switch in your HVAC or automotive climate control system. Its main purpose is to turn the blower fan on and off and control its operational speeds.
When a blower motor relay goes bad, it fails to act as the electrical switch that directs power to your heating or cooling system's fan. This typically results in complete loss of airflow, the fan getting stuck on a single speed, or the fan refusing to turn off.
Contact wear and corrosion are two of the most common. Relays can develop wear and arcing damage from the repeated operation, and it can also result in circuit failure. Contact wear and arcing damage can lead to high contact resistance and short-circuiting.
Blower motor control: The main role of the blower motor relay is to control the operation of the blower motor. It receives signals from the thermostat or HVAC control system to start or stop the blower motor as needed. Speed control: Blower motor relay also controls the speed of blower motor.
A bad fan relay fails to send electrical signals from the control module to the fan motor. The most common symptoms include an engine that overheats while idling, poor A/C performance at low speeds, a radiator fan that fails to turn on, or a fan that runs constantly and won't turn off.
Testing a blower motor relay involves a quick "swap test," an audible click test using a 12V battery, and a continuity check using a multimeter. This helps determine if your HVAC issues stem from a faulty relay, a blown fuse, or the blower motor itself.
Nearly all of the relays on a car, including the blower motor relay are built to last for as long as the car does.
To determine if a relay is blown, you can perform a simple swap, a click test using a battery, or a thorough diagnostic with a multimeter. A blown relay usually causes a component to stop working entirely or operate intermittently.
The blower motor relay is typically located in either the under-hood power distribution box (next to the battery) or the interior fuse box usually positioned beneath the driver's side dashboard. In some vehicles, it is built directly into the blower motor resistor or mounted behind the glove box.
Resetting a blower motor typically involves cycling the power, checking for tripped thermal switches, or adjusting your thermostat. These methods apply to residential HVAC systems, though the exact steps vary depending on whether you are working on a furnace, an AC unit, or a car's blower motor.
Common indicators that a relay is malfunctioning include unusual clicking noises, failure to activate, and intermittent operation. These symptoms can signal underlying electrical relay problems that require attention.
A relay's lifespan depends on its type, the electrical load it handles, and its environment. In general, mechanical relays last 1 to 5 years (or 100,000 to 1,000,000 cycles), while solid-state relays (SSRs) can last 10 to 15-plus years.
Excessive Heat
Just as cold weather and moisture can damage relays, excessive heat can also shorten their lifespan. In vehicles, for example, high engine temperatures or a poorly ventilated fuse box can cause relays to overheat, triggering electrical malfunctions.
The average cost for a Blower Motor Relay Replacement is between $109 and $133. Labor costs are estimated between $50 and $73 while parts are priced between $59 and $60. This range does not include taxes and fees, and does not factor in your unique location.
To quickly tell if your car's HVAC issue is the blower motor or the resistor, look at your fan speed settings. If the fan works only on the highest setting, the resistor is usually the culprit. If the fan fails completely on all speeds, or struggles and stutters, the blower motor is likely failing.
Symptoms of a Bad HVAC Fan Relay
It doesn't always fail outright — it can stick, misfire, or stop responding. Here's what to watch for: Blower fan won't start. Fan keeps running even when the system is off.
A bad blower motor relay acts as a faulty switch, preventing electrical current from reaching the fan. Common symptoms include a blower fan that does not turn on at all, a fan that stays running even when the vehicle is off, weak or inconsistent airflow, or clicking sounds from the dashboard.
The blower motor resistor can be removed after the bolts have been removed. The wire should be linked to the blower motor's positive terminal, and the negative terminal should be attached to the blower motor's negative terminal. This will turn off the resistor and allow the blower motor to run at full speed.
The blower motor fuse is typically a 20-amp to 40-amp fuse. Because fuse locations and sizes are highly specific to your vehicle, you'll need to check the exact year, make, and model's owner's manual or fuse box diagram. Common locations include the engine bay or under the dashboard.
Set your multimeter to resistance mode and probe the two coil terminals (pins 85 and 86 on a standard five-pin relay). A healthy coil reads between 50 and 120 ohms on most relays. A reading of zero indicates a short, and an open-loop reading (OL) means the coil is broken and the relay needs replacement.
The method to reset a relay depends entirely on the type of relay you are using:
Yes, a bad relay can still click.
Knowing the common causes of blower motor failure and how to fix them can save much time and money.
The blower relay has an important function and role in automobiles. It controls the starting and stopping of the blower and its speed to ensure proper air circulation and temperature inside the car.
The heat exchanger is often considered the most costly part of a furnace to repair or replace. It is a critical component that transfers heat from the combustion process to the air that circulates throughout your home. Over time, heat exchangers can crack due to the constant heating and cooling cycles they undergo.