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Automotive/84 F 150 blower motor resistor

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Expert: - 10/25/2007


Question
QUESTION: since my blower motor only works on high I beleive the resistor is bad.  the resistor on this vehicle consists of three coils of wire of varying gauge and an insulated resistor which has no identifying markings whatsoever.  I would like to find out what the ohm and watts of this this insulated  resistor is so that I can change it out.  thanks.

ANSWER: My E250 is a 78, but close enough in vintage that I likely do have the information in the manual or electrical-and-vacuum book for mine.

I shall get back to you in a day or two.  For this evening, I am staying around the office to get ahead on a stack of assignments.

Regards ... EGK

PS 20071024

The electrical/vacuum book does not give the values for the resistances involved, although the shop manual might, and I'll borrow back my copy so I can check that out.  Failing that, I can pull out my good resistor module from the blower housing, and use my Fluke 1520 (MegOhmmeter, also with a tare-able ultra low-ohms range) to do a measurement on the component resistances.  Cycling the fan as well and measuring the current through each would allow assessment of actual power dissipation, and ratings can be derived from these.  The resistors appear to be mounted in the fan housing airstream upstream of the heater core, to get some active cooling from the supply air.

I can do this if I am doing any work on my E250 this weekend, which I will be should it transpire that I cannot get away for a contemplated trip out of town.    Weather and other work load issues tend to set such trips on the sidelines more times than I like ... !

Later yet again ... EGK

---------- FOLLOW-UP ----------

QUESTION: thanks for your help..no need to pull yours apart.  i went ahead and removed the insulated resistor and jumpered in a 14 ga insulated wire in place of the bad resistor.  it works fine...maybe not the exact low and medium factory speeds but it works.  does not appear to be overheating the wire or the wire resistors.  phil

Answer
You got me curious anyway; besides, it would be worth my while to know the values of these resistors while they are presently working, in case I have to come up with a work-around at some time in the future.  Actually, I would probably work out a pulse-width modulator circuit as a replacement, so that the fan speed can be continuously variable ... and then maybe tie the PWM circuit into a thermostatic control circuit ... now, you really have me going!  Well, during my next refit perhaps.

Still, I had one thought about the insulated resistor you mentioned.  I haven't checked mine out yet, but wonder if this is one of those power resistors that is a wire-wound type in a ceramic package.  If so, it might be a common type, from which the power rating can be determined by package size.  The packages are square cross-section, and the smallest version is the 5W version, for which the package is 1 inch long and 3/8-inch across.  The 10W version is the same cross section, but 2 inches long.  The 20W version is also 2 inches long, but is either 1/2 or 9/16 inches across (sorry, I have neither one of those nor my caliper at my desk).

Whether that is the type or resistor used or not, you might consider that type of resistor as a type to use if you want to get back your low and medium speeds.  I will do the measurements anyway, just to have the info.

Regards ... EGK

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Ernest (Ernie) Kenward

Expertise

The challenges I most enjoy are thoughtful technical questions of a trouble-shooting nature in both electrical, power electronic and mechanical systems, mainly automotive but also machine control and small-machine PLC applications. Please note, however, that I am NOT a walking shop manual! I DO, however, make it a point to have those manuals and other service literature for those vehicles I DO own, and highly recommend that anyone serious about maintenance or modification of their vehicles do the same; MOST of your answers WILL be found there. For that matter, I do NOT go out of my way to acquire shop manuals for any vehicle I do NOT own! That being the case, any general query to me along the lines of "What is the meaning of this code read from the ECU of my 2015 XYZ?" or "Where is the fuse for the windshield washer pump found?" (try your car's electrical distribution panel for a start!) will not go far. What I do offer is a pretty good collection of literature, insights and hands-on experience with 1950s to 1980's Ford products (plus a developing database of information and practice with the Mercedes diesel cars), along with an engineering perspective and the ability to design and implement custom control, electrical and mechanical subsystems for vehicles. For that reason, I am happy to make my thoughts and efforts available to those who are of like mind and/or are seriously making a point of learning about their vehicles. Use the Opportunity to Learn!

Experience

A key skill in my work and hobby pursuits both is STRATEGIC TROUBLESHOOTING. I am a senior instructor in Electrical Engineering Technology at a leading Canadian polytechnic, my areas being Electrical Power and Industrial Control, electrical and electronics design and manufacturing, and AutoCAD and related CAD/CAE software - plus equipment problem-solving and new equipment design and prototyping. Hobby-wise, I have 30-plus years of experience in auto restoration, mostly in electrical and mechanical systems. Ongoing projects include a 1959 Edsel Corsair, my 1978 Ford E250 class-B motorhome conversion, and the care and upkeep of my Mercedes 300CD. My vehicles become engineering test beds for electrical and mechanical upgrades as ideas present themselves. This includes the design and production of circuit boards to restore or enhance features for which no OEM replacement parts are obtainable, or where better specifications or reliability can be had via newer concepts. Regarding the E250 RV conversion, I designed and continue to revise a custom power distribution system, managed by a Programmable Controller (PLC); this has made most revisions as easy as uploading new firmware as I develop it. The "mini" PLC is a powerful device for custom automotive control systems. One good example (there are many) would be the Moeller "Easy Relay"; these offer a wealth of control, monitoring and variable-and-status display options for such projects. A good example project which has worked well is that one for my RV noted above, which has been on the job - revised in firmware only - for a decade now. It is a load management and charging control system to avoid the sulfation-induced early failure that often befalls deep-cycle batteries used in RV power applications. The battery installed in 2003 lasted long enough to more tnan pay for the PLC that contributed to its longer life ... and the PLC will be there for the next battery as well!

Organizations
IEEE - senior member ... past WCC Student Activities; SME - senior member ... past chair, greater Vancouver chapter chair 318; Edsel Owners' Club - have served in various capacities on chapter executive during seventies; have been Power and Driveline resource on the Edsel Owners' Club "E-team" for more than a decade.

Education/Credentials
Graduate of UBC

Awards and Honors
Certificates of appreciation from IEEE and SME for work in student and chapter activities

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