How to Test a Blower Motor Relay with a Multimeter: Step-by-Step Guide

Your car's AC or heater suddenly stops blowing air, and you're stuck sweating or shivering behind the wheel. Before you rush to a mechanic and spend money you might not need to, there's a quick diagnostic check you can do yourself with a basic multimeter. Knowing how to test a blower motor relay with a multimeter step by step can save you time, money, and the frustration of replacing the wrong part. The blower motor relay is a small, inexpensive component, but when it fails, it cuts power to your entire climate control fan. Testing it properly takes about 15 minutes and requires no advanced skills just the right approach and a multimeter set to the correct mode.

What Does a Blower Motor Relay Actually Do?

The blower motor relay is an electrically controlled switch. It sits in your vehicle's fuse box and acts as a gatekeeper between your car's battery and the blower motor the fan that pushes air through your vents for heating, cooling, and defrosting. When you turn the fan dial or press the climate control button, a small current energizes the relay's coil, which closes a heavier internal contact and sends full battery voltage to the blower motor.

This design matters because the blower motor draws too much current for a dashboard switch to handle directly. The relay does the heavy lifting. If the relay's internal coil burns out or the contacts corrode and stick, the blower motor gets no power even though the motor itself might be perfectly fine. Understanding this distinction helps you avoid confusing the relay with the blower motor resistor, which is a different part that controls fan speed, not on/off power.

What Tools and Preparation Do You Need?

Gather these items before you start:

A digital multimeter one that can measure resistance (ohms, Ω) and continuity. Most affordable meters handle this fine.
Your vehicle's owner's manual or a fuse box diagram to locate the relay position.
A relay puller or needle-nose pliers to remove the relay without damaging surrounding sockets.
Clean, dry hands and a well-lit workspace moisture or poor visibility leads to wrong readings.

Turn off the ignition and, for extra safety, disconnect the negative battery terminal before pulling any relay from the fuse box. This prevents short circuits or blown fuses while you work.

Where Is the Blower Motor Relay Located?

Most vehicles have the blower motor relay in one of two places:

Under-hood fuse box typically on the driver's side near the battery or firewall. This is the most common location in sedans, trucks, and SUVs.
Interior fuse panel under the dashboard near the steering column or on the side of the dash (accessible when the driver's door is open).

Check the diagram printed on the fuse box cover or in your owner's manual. Look for a label like "BLOWER," "HVAC," "BLOWER RELAY," or "HEATER FAN." The relay is usually a small rectangular cube, either a standard 4-pin or 5-pin automotive relay, plugged into a socket in the fuse box. If you're unsure which relay type your car uses, the pin count affects how you test it but the core process is similar for both.

How Do You Test a Blower Motor Relay With a Multimeter Step by Step?

Step 1: Remove the Relay From the Fuse Box

With the ignition off and the battery disconnected, use a relay puller or pliers to gently pull the relay straight out of its socket. Avoid rocking it side to side, which can bend the pins. Once removed, inspect the pins for visible corrosion, burn marks, or bent contacts. Heavy corrosion alone can cause a failure.

Step 2: Identify the Relay Pin Layout

Most blower motor relays follow a standard layout. Look at the bottom of the relay the pins are numbered (usually 85, 86, 87, and 87a for a 4-pin relay, or 85, 86, 87, 87a, and 30 for a 5-pin relay). Here's what each pin does:

Pin 85 and 86 the coil circuit (control side). When voltage is applied across these pins, the relay activates.
Pin 30 the common terminal (power input from the battery).
Pin 87 the normally open (NO) contact. This is where power flows to the blower motor when the relay is energized.
Pin 87a the normally closed (NC) contact. Power flows here when the relay is not energized (used in some designs, not all).

Check the relay's printed diagram or datasheet for your specific vehicle if the layout differs.

Step 3: Test the Coil for Continuity (Pins 85 and 86)

Set your multimeter to the resistance (ohms/Ω) mode, ideally on the 200Ω or auto-ranging setting. Place one probe on pin 85 and the other on pin 86. A good relay coil should read between 50 and 120 ohms (exact range varies by relay manufacturer). If the meter reads "OL" (open loop/infinite resistance) or shows zero, the coil is broken or shorted and the relay is bad.

Step 4: Test the Normally Open Contacts (Pins 30 and 87)

Keep the multimeter on resistance/continuity. With the relay not energized (no power applied), place one probe on pin 30 and the other on pin 87. You should get "OL" or infinite resistance meaning the circuit is open, which is correct for normally open contacts. If you get a low resistance reading, the contacts are stuck closed, and the relay is faulty.

Step 5: Test the Normally Closed Contact (Pins 30 and 87a) If Applicable

If your relay has pin 87a, test between pin 30 and 87a with the relay de-energized. Here, you should see very low resistance (close to 0 ohms) or a continuity beep. This means the normally closed path is working. No continuity here indicates worn or corroded internal contacts.

Step 6: Energize the Relay to Confirm Full Operation

This optional but helpful step confirms the relay works under power. Reconnect the battery temporarily. Apply 12V from the battery (using jumper wires) across pins 85 and 86 pin 85 to ground, pin 86 to positive, or vice versa depending on your relay. You should hear or feel a click. While the coil is energized, test between pins 30 and 87 with your multimeter it should now show near-zero resistance or continuity, meaning the relay successfully closed the power circuit.

If you hear the click but get no continuity between 30 and 87, the contacts are burned or corroded inside the sealed relay housing. The relay needs replacement.

How Do You Know If the Blower Motor Relay Is Bad?

A bad relay usually shows one or more of these symptoms:

No air from vents at any fan speed the most common sign. The blower motor is completely dead even though the rest of the climate system works.
Intermittent fan operation the blower works sometimes, then cuts out randomly. This can indicate a relay with worn contacts that make and break connection unpredictably.
Fan only works on one speed this is more commonly a resistor issue (learn more about the difference between the relay and resistor), but in some circuits the relay plays a role in high-speed operation.
Relay clicks but the motor doesn't spin the coil works, but the internal power contacts aren't making a connection.
Burnt smell or visible melting near the fuse box severe relay failure can cause heat damage to the socket.

What Common Mistakes Should You Avoid?

Testing a relay is straightforward, but a few errors can send you down the wrong path:

Testing with the relay still plugged in you need it removed from the circuit for accurate resistance readings.
Using the wrong multimeter setting testing continuity with the meter on DC volts gives meaningless numbers. Make sure you're on the ohms/resistance or continuity function.
Skipping the coil test many people only check the contacts. A bad coil means the relay never activates at all.
Confusing the relay with the resistor both sit in the blower circuit, but they fail differently. If your fan works on high but not on lower speeds, the resistor is the likely culprit, not the relay.
Not checking the relay socket sometimes the relay is fine, but the socket contacts are corroded or loose. Inspect the socket terminals for green corrosion or widened contact points.
Assuming a clicking relay is a good relay a click means the coil works, but burned contacts can still prevent power from reaching the blower motor.

What Should You Do After Testing?

If your multimeter tests confirm the relay is faulty, replacement is simple and affordable. Most blower motor relays cost between $5 and $30 at an auto parts store. You can see a detailed breakdown of parts and labor in this relay replacement cost and parts guide. Just press the new relay into the socket no tools needed beyond what you already used to remove the old one.

If the relay tests good, move on to checking the blower motor itself with the multimeter (test for resistance across the motor terminals), inspect the fuse for the blower circuit, and verify the ground connection. The relay is only one link in the chain.

Quick-Reference Testing Checklist

Turn off ignition and disconnect the negative battery cable.
Locate the blower motor relay using your fuse box diagram.
Remove the relay carefully with a puller or pliers.
Set multimeter to ohms (Ω).
Test coil resistance between pins 85 and 86 expect 50–120Ω.
Test NO contacts between pins 30 and 87 expect OL (open) when de-energized.
Test NC contacts between pins 30 and 87a expect near 0Ω when de-energized.
Optionally energize the relay with 12V and re-check pins 30–87 for continuity.
Compare all readings to decide: replace the relay, or investigate other components.

Pro tip: If you buy a replacement relay and it doesn't fix the problem, keep the receipt but also check the relay socket under a flashlight. Corroded or melted socket terminals are a hidden cause that mimic a bad relay. Cleaning the socket contacts with electrical contact cleaner and a small pick can sometimes restore a connection without any part replacement.