Look at the resistor first. That seems to be the most common place for this problem, mainly because of its location.

 

I have the same issues with our 2002 F-150.It only works on high,and lately it is starting to smell like wires burning.

 

I'd also like to thank the OP. My fan speeds 1 and 2 stopped working about a month ago along with a burnt wire smell. Now today speed 3 also stopped, leaving me with only high speed. I came on here, did the search and came upon this awesome post along with pics and everything. This really is a great site! I'm going to take a look at it later today and see what I find.

 

Yup, sure enough the resistor was bad. Pulled it out in the parking lot of the auto parts store. Luckily the plug was ok. Chunks of rust were fell off when I set it on the counter. Pretty bad shape.

 

My 1st time to this site and had to thank you for the great detailed photos and instructions......a $26.00 part at Napa and 20 minutes and I now have all 4 speeds back. Bluebobbybird, the photos were some of the best I have ever seen, the detail couldn't have been better. THANKS ('99 F150 XLT 5.4)

 

Just did this repair in about 10 minuets. What a great fix and write up. My blower would only work on High also in my 2001 F150 Supercrew. This will be great to now have 4 blower settings.
Great write up BlueBobby. A real life saver.

 

Thanks Bluebird, you saved me over $250. I also repaired my connector.
The clown at the Ford dealer wanted $300 to fix mine.
Great photos!!!

 

I had the same problem as BlueBobbyBird in my 1999 F150 last week; the harness melted at the connector and the resistor was rusted but not as bad. I replaced both and the fan worked on all four speeds...for one day. Now I have no speeds. I double checked the connections which are all good. It did not melt again. I also checked the mini fuses under the dash as well as the maxi fuse in the engine compartment; none of those are blown. It seems strange that I had high speed only before replacing everything, got all four back and now nothing???

Is it possible for the switch to go bad? Can someone walk me through testing the components? Or, is it time to throw my hands in the air and take it somewhere? Gotta have the defroster already here in Michigan at night!

Thanks in advance!

 

It sounds like the resistor element itself has blown. Take the plug off, remove the screws that hold the resistor in, and inspect it closely. If there is any break in the wires, that's your problem. They're cheap, and relatively easy to replace.

 

Thanks a lot for the great thread. I had purchased a resistor, turns out it was the wrong one anyway. When I removed the existing one to make sure they ordered the correct one I noticed the burning, (mine was much worse than the pictures). The resister was corroded but still worked so I just rebuilt the connector and it works like a charm. Thanks again I would not have known which wires to pull without the pics.

PS Should Ford not be worried about lawsuits when the vehicles catch fire because of this, mine must have been very close.

 

Wonderful thread.

First, let me say that BlueBobbyBird's photos were some of the best I've seen for troubleshooting. Thanks a million.

My 1999 F150 lost all but the high speed of the blower about three weeks ago. I suppose it could have lost the lowest speed, but I can't hear that most of the time anyway, so I really can't say it was lost.

Following BlueBobbyBird's photos and my Chilton manual, I was able to find the wire harness with its three plugs, and the resistor block.

I disconnected the three plugs of the wire harness and saw that the white plug of the wire harness had its plastic scorched and melted-away around the usual receptacle.

Then I pulled the resistor block and saw its corresponding conductor blade showed signs of overheating--the black plastic of the connector was melted around the blade corresponding to the receptacle of the white plastic plug of the harness. The three resistance coils were in perfect shape, and I think the thermal limiter was OK, too. (I measured it with a volt-ohm meter and it read high resistance one way and low the other, and I hope that means it's OK.)

I fiddled around, scraping the metal of both blades and receptacles--of the block and of the white plug of the harness. After about a day of dithering, I put the block back in and then reconnected the harness. I turned on the heater blower switch, and it again works on all speeds.

I'm guessing a high resistance developed at the contact between that particular receptacle of the white plastic plug and its corresponding blade contact of the resistor block connector. The high resistance caused heat and caused the melting. Eventually the resistance (from corrosion, probably) interrupted the current for all but the high speed setting. When I disconnected the block from the white plastic plug, this might have rubbed-off some of the corrosion products and left good metal. The scraping I did while the components were out may have helped, too.

Before I found that the speed control was working again, I ordered a replacement "blower resistor kit", Dorman 973-414, from RockAuto, and it is in the mail as I type, and cost $33.80, shipping to North Dakota. The kit has the resistance block and the white plastic plug with pigtail wires, so I'll just cut the old connector off and splice the new one into place and should be "good to go." I intend to follow ExTex's good advice and smear some anticorrosion grease on the contacts between the new block and the new white plastic plug.

As for the $33.80, I suppose I should consider that money an insurance premium, because who knows how long the "fix" I did on the old connector and the block is going to last?

 

I have the same problem with the fan only working on high and will be checking this resistor momentarily but I also have another symptom that occurred at the same time. The temperature does not seem to adjust at all. It does not get to cool or hot. This started at the same time as the problem with the fan speeds.

Has anyone else had this problem?

 

I had a similar problem. Glad I checked here. I didn't know about the resistor pack. Thought it might be the switch or the motor. I had speeds 3 and 4 working so I pulled the resistor pack. The connector was in good shape so I didn't have to deal with that. After inspecting the resistors I saw the problem; the second resistor was broken off the connection. Went to Napa Auto, $19.99 + tax and put it in pretty quick.

 

Overheating and corroding connections on the blower system is not just a problem on F150s, or even on Fords. I have had exactly the same problem on a Chevy van, a Dodge minivan, and I have even fixed the same basic problem on a Mercedes sedan! Apparently, running the blower on "high" for extended periods of time (maximum current draw) is what leads to the difficulty: if one contact somewhere is making slightly less than perfect contact, it generates heat, which accelerates oxidation (corrosion), which creates more resistance, which makes more heat, etc.
How do we avoid this issue? Well, I don't know about the rest of you, but I have gone through all the connectors on the blower circuit on all (3) of my cars, cleaned the blades and sockets, and coated them with DC-4 silicone grease. I also make it a practice to limit the amount of time I run the blower on high, and have instructed my wife to do so as well, under penalty of having to fix it herself if she burns up a connector! It's been working for over a year, and I have high hopes for the future.

 

What a great thread. Can't wait until tomorrow when I can look at my 1997 F150 which only has two speed on the fan left. In the spring I will check my 1999 Ford/Winnebago Motor home which only has the high speed left.

This seems so simple but when I had the motor home into Ford the Tech said it would be too costly to fix. Can't wait to see what the real problem is.