I know the feeling all too well – rushing on a frosty morning only to find that the rear defroster in my F150 has stopped working. It’s happened to me before, and let me tell you, it’s not a pleasant surprise.

Turning to forums and talking with other F150 owners, I realized I wasn’t the only one facing this issue. After exploring various reasons behind this problem, I finally cracked the code and found solutions. In this article, I’ll be sharing those fixes with you.

Why Is My Ford F150 Rear Defrost Not Working?

If your Ford F150’s rear defroster isn’t working, it could be caused by a blown fuse, a delay in window closure, or faulty connectors. To solve this problem, inspect and replace any blown fuses, adjust the window, or ensure all electrical connectors are clean and secure. For more complex problems, refer to the F150 Factory Service Manual or get help from the dealer.

As usual, I’ll start by going through all the root causes I’ve come across that can cause this issue:

1. Blown Fuse

A blown fuse can break the electrical path for the rear defrost system, preventing the defrost elements on the rear window from turning on.

2. Defrost Contact Points Not Closing Properly

When your rear window goes a bit too far when closing, it doesn’t connect to the defrost contact points.

This can happen because of wear and tear or a mechanical glitch.

3. Faulty Connectors

Worn-out or burnt-out internal connectors in the defrost system increase electrical resistance.

This resistance hampers the power flow to the defrost elements, causing a noticeable drop in effectiveness or complete failure of the rear defrost.

4. Sensor Disruption in Sliding Window Models

Sliding window models feature sensors along the frame with fingers that detect the window’s position.

As the window closes, these fingers push against internal contact points, signaling the system to activate the defogger.

If these sensors or connections get dirty, it can cause increased resistance or misreporting, hampering the defrost system.

5. Faulty Blend Door Actuator

A malfunctioning blend door actuator messes with the temperature control in the climate system.

This results in insufficient warm air circulating for effective defrosting, making it harder for the defrost elements to clear frost or condensation on the rear window.

The defective blend door actuator can also make your truck’s heater blow cold air.

6. Faulty Rear Sliding Window (2011-2013 F150s)

Sometimes, the rear sliding window might just be broken, causing sensors to trip and show it as open, preventing the rear defogger from working.

This is a common scene across 2011–2013 F150s.

How To Repair F150 Rear Window Defogger?

Now, let’s go through everything you can do to get your defogger back in working order:

Solutions For F150 Rear Defrost Not Working

1. Check And Replace The Fuse

  • Peek into the fuse box for the rear defrost fuse.
  • Use the fuse diagram to spot the right fuse.
  • Swap out any blown fuse with a new one of the same amperage.
  • Give the rear defrost a whirl to check if it works again.

2. Fix Improper Window Closing Issue

  • Close the rear window completely.
  • Find the controls for adjusting the rear window’s position.
  • Use the controls to move the window slightly downward.
  • Lower the window by about 1/16″ or less.
  • Check if the window now closes without going too far.
  • Test the rear window defrost function to ensure it’s working.
  • If issues persist, repeat the process in smaller increments.
  • Open and close the window, ensuring proper movement and defrosting.

3. Fix The Connectors Of Defrost System

  • Use a multimeter to check the voltage at the rear defroster grid.
  • Refer to the wiring diagram to identify key components in the rear defroster circuit.
  • Probe the purple wire at the rear defroster switch to check power output.
  • Identify excessive resistance if there’s a significant voltage drop.
  • Trace the circuit using the wiring diagram to find potential points of resistance.
  • Inspect connectors for damage or burning; in most F150s, the issue is usually with connector 220.
  • Unplug each connector and check for voltage irregularities on the purple wire.
  • Replace damaged connectors, ensuring proper soldering.
  • Verify power output at the rear defroster grid after replacing the connector.
  • Reassemble dashboard components carefully.
  • Test the rear defroster and HVAC controls for proper operation.
  • Start the car and check for warning lights or issues after the repair.

If you’re having trouble and need help, you can check out these two videos. Here’s part 1:

Here’s part 2:

4. Fix Sensors Of Sliding Window Models

  • Find the contact casing at the bottom right of the sliding window and take it off.
  • Inspect the connectors for dirt or debris.
  • Gently clean connectors with a soft brush or cloth.
  • Check for bent pins or corrosion on the connectors or fingers.
  • Securely put the contact casing back in place.
  • Operate the sliding window to check for proper movement.
  • Run the defrost system to see if the issue is fixed.

5. Replace Blend Door Actuator

Now, this one is a rare cause when it comes to the issue, but it can help sometimes and also get rid of other glitches plaguing your HVAC system such as AC not blowing cold air.

  • Remove the side panels and trim around the radio.
  • Lift the top trim and use a 7-mm socket to remove the hidden bolts.
  • Pull out the radio panel, disconnect the top connectors, and remove four screws with a 7mm socket.
  • Pull out the radio and disconnect all connectors.
  • Locate and remove screws on the black actuator behind the radio.
  • Lift the actuator, disconnect wiring, ensure gear alignment, and insert a new actuator.
  • Reconnect all radio connectors, slide it back in, and secure with four screws.
  • Reattach trim panels and bolts.
  • Reset the new blend door actuator by removing the HVAC fuse.
  • Test to see if the rear defogger works.

6. Replace The Faulty Window

This is a complex fix. It’s usually covered under warranty, so consider taking the truck to the dealer.

Use these steps as a simplified reference; consult your own F150 Factory Service Manual for details about your specific model.

Below is a summary of steps for a 2017 Ford F-150 Platinum.

  • Open the rear sliding window fully.
  • Use long-nosed pliers to remove the carrier guide.
  • Detach right and left stops, release cable tension, and remove stop screws.
  • Disconnect the electrical snap tab from the right side and pry it from the glass.
  • Remove the rear sliding window.
  • Use an interior trim remover to press cable nuts and springs.
  • Install the new rear sliding window, connecting the electrical snap tab.
  • Install the carrier guide.
  • Attach left and right stops and cables, securing them with lifted cables.

Follow torque specifications and use specified adhesive (in this case, 3M™ Super-Fast Repair Adhesive) during installation.

FAQs

Has there been a Ford F150 rear window defroster recall?

Unfortunately, there hasn’t been a Ford F150 rear window defroster recall, despite reports of windows exploding. Recalls usually involve cases of severe injury or death.

How to bypass rear defrost in F150?

Unplug the wire from the rear defrost connector at the window and give it a little tape job. Don’t worry if the mirror defrost button doesn’t light up; it’ll still work. You can also pull out relay #4 near the back center of the fuse block under the hood. Just a heads-up, though your heated mirrors will lose power too.

Final Thoughts

Try these fixes and bring back your F150’s rear defrost in shape. You won’t have to fret about obscured visibility or safety concerns anymore. 

Now, as you hit the road, enjoy the peace of mind that comes with a crystal-clear rear window.

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