Here's a general procedure. The specifics might vary slightly depending on the year and model of your Chevy truck, so consulting your vehicle's repair manual is highly recommended.
1. Locate the Blower Motor Relay:
* Under the Hood: This is the most common location. The relay is often found in a fuse box or relay center, usually located under the hood near the battery. Your owner's manual or a quick online search (e.g., "[your Chevy truck year and model] blower motor relay location") will help pinpoint the exact location. The relay itself may be labeled, or you might need to consult a fuse box diagram.
* Inside the Cab: Less common, but some models might have the relay inside the cab, often near the fuse panel under the dashboard.
2. Identify the Blower Motor Relay:
* Visual Inspection: Relays are usually small, square or rectangular components with multiple terminals. They may be labeled (look for "blower motor," "HVAC," or similar). If unsure, use your owner's manual's fuse box diagram.
* Testing with a Multimeter (Preferred): Even if you think you've found the right relay, a multimeter is the surest way to confirm. *This is described in step 3.*
3. Test the Blower Motor Relay:
You'll need a multimeter set to ohms (Ω) to test the relay's continuity.
* Remove the Relay: Carefully remove the relay from its socket.
* Continuity Test: Most blower motor relays are simple switching relays. They have four terminals:
* 85 & 86: These are the coil terminals. There should be continuity (a low resistance reading, close to 0 ohms) between these two terminals.
* 30 & 87: These are the contacts. *There should be NO continuity between these two terminals when the relay is unpowered.* With the coil energized (see next section), there *should be* continuity.
* Check for Open or Shorted Contacts: If you find no continuity between 85 and 86, or continuity between 30 and 87 when the relay *should not* be conducting, the relay is likely faulty. If you find continuity between 85 and 86, and no continuity between 30 and 87 when it *should* be conducting, try energizing the coil (next step).
4. Energizing the Relay Coil (Optional, requires power source):
This step will require you to apply power to the coil terminals.
* Caution: Be careful not to short anything and potentially damage your truck's electrical system.
* Use a Test Light or 12V Power Source: Connect one lead of a test light or a 12V power source to terminal 85 (or 86). Connect the other lead to terminal 86 (or 85) – this should momentarily energize the relay's coil.
* Check Continuity: While the coil is energized, test for continuity between terminals 30 and 87. If you now have continuity, the relay is likely working correctly. If not, the relay is likely faulty.
5. Replace the Relay:
If your tests indicate a faulty relay, replace it with a new one of the same rating. You can find replacement relays at most auto parts stores. Make sure to get the correct amperage relay for your system.
Important Considerations:
* Always refer to your owner's manual: It contains specific diagrams and information for your particular truck model.
* Fuse Check: Before blaming the relay, check the related fuses for your blower motor. A blown fuse could be the actual problem.
* Blower Motor Itself: If the relay tests good, the problem might lie with the blower motor itself or its wiring.
If you're uncomfortable working with car electrical systems, it's always best to take your truck to a qualified mechanic. Improper electrical work can cause damage or injury.
