73-87chevytrucks.com
73-87 Chevy _ GMC Trucks => Electrical => Topic started by: pholliday1 on December 21, 2012, 11:44:25 am
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I have yet to trouble shoot this issue, fan only works on hi, if i remember fan speed is controlled by resistor "Three prong" and is mounted with close proximity to fan motor. However upon inspecting my firewall area opposite where the fan motor is,more closer to the distributor (right below the fuel relay for tbi trucks on the heater box) i've found another male three prong plug similar to the other one with no wires going to it.So my question is does anyone know the ohms reading for a good resistor and what the heck is this other plug? Truck ia a 1990 crewcab with 1990 suburban interior.
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Blower resistors are pretty simple. Don't bother trying to measure it - the resistance values are pretty low. Instead, take it out and look at it. If it appears burned - replace it. If it doesn't - it's okay. But, if the resistor is burned there are other issues that need to be addressed, such as poor air flow within the ducts or a faulty blower motor that pulls excessive current. Blower resistors don't fail nearly as often as the blower switches.
On the extra plug - can you post a pic?
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Copy..on the idea there's more to it,probably fan motor good info thanks give me a few and ill get pic
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mine was doing the same problem. now i know i cleaned out the leaves in the air duck maybe that caused the extra work on the resistor. but replaced the resistor about 2-3 years ago and no problems
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Found resistor very clean (spring portion) however the long metal pieces that connect prongs to the springs are extremely rusty ordered new resistor from napa 17 bucks replacing it in am. I wrongly called it a three prong connector it's actually has 4. Will get pic on mysterious extra 3 prong soon .
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The resistor coils are just crimped to the terminal stands . . . so corrosion in the 'crimps' . . . could really "crimp" the motor's style (result in excessive voltage drop). :o
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Using a test light with the resistor unplugged and ignition switched ON, cycle the blower switch through the various fan speeds. In each switch position probe the resistor wire connector. Brown/white is low fan and should be hot whenever ignition is switched ON. Tan should be hot only on medium-low fan. Light blue should be hot only on medium-high fan. Dark blue is the jumper wire between the relay and the resistor, so will never be hot as long as the resistor is unplugged. Orange connecting to the blower relay is high speed and you already know it works.
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Installed new resistor all is well. Thank you BD for responding I've read several threads that you have given insight on and I want to say thank you for sharing the knowledge you have, you are defiantly a big asset to this forum
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Thanks
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YIKES! Fan motor back to just working on hi. Followed BD's steps to the letter found voltage at the correct spots plugged everything tested purple wire(fan motor wire) with test light and found that the test light lit on all speeds ,reconfirmed fan motor ground to be good. Does all this mean my fan motor is faulty?
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With everything connected and your voltmeter negative lead attached directly to battery negative, measure the voltage at the blower motor for each fan speed. Post your measurements.
Also, probe blower motor case to battery negative with blower on high - should measure 0 volt.
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Copy will do! Also found blower motor very "free wheeling" with little to no resistance. Just want to make sure I do proper trouble shooting.
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Your interest in troubleshooting is commendable... and, when you have the time, less costly. When you're done, you'll be an expert at troubleshooting blower circuits. 8)
The more you describe the more it sounds like a worn out blower motor. If you wind up replacing the motor, consider purchasing for a 1994 C/K1500. It pushes considerably more air. Just make sure the hole for the motor vent is the same size.
IIR, the newer motor went into production with or shortly following the advent of modular A/C, which supplanted cables and vacuum motors in the subsequent generation.
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Curious. Did you figure out the extra plug? ???
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"Hole for motor vent same size"? Are you referring to rough opening the fan motor fits at the fire wall? And do I purchase a new squirrel cage? I like the tip about moving more air.
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The squirrel cage should come with the motor (http://www.napaonline.com/Catalog/CatalogItemDetail.aspx?R=BK_6551744_0365920569). A rubber elbow attaches between the motor housing and the air box. Make sure the opening in the motor housing is the same diameter as your original.
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Took voltage readings as follows... 11.68v on high and 11.62v at the other settings. Very confused, Is the speed controlled by reduced voltage or reduced amps? or both? Will post picture of three prong plug still not certain on its function
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Sorry for the delay, been under the weather.
Just to be clear: The blower only runs on high speed; and only when the blower switch is set to high. It doesn't run at high speed on all switch positions. True?
Unplug the blower relay. Temporarily jumper the blue wire to the purple wire. If the voltage measurements are the same, replace the blower motor. If the voltage measurements change or the blower starts working, replace the bower motor and the relay.
Took voltage readings as follows... 11.68v on high and 11.62v at the other settings. Very confused. Is the speed controlled by reduced voltage or reduced amps? or both?
Voltage, current and resistance are related in a very exact way, represented by Ohm's Law: Voltage = Current X Resistance (Volts = Amps X Ohms). If resistance is fixed at a constant value, then a decrease in voltage will cause a decrease in current. Similarly, an increase in voltage will cause an increase in current. The resistor uses some of the voltage across the blower circuit, wasting it as heat, hence causes a decrease in voltage available to the motor.
With regard to an electric motor there are other considerations, because of the magnetic field - the interaction between the magnetic field and current flowing through the motor windings that causes the effective resistance (reactance) of the motor to vary from its measured resistance. But, even with the added complexity, it still boils down to the mathematical relationship represented by Ohm's Law.
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Correct motor only works when switch is on hi and it will not work at all in any other position. Here is a picture of the three prong plug sorry its sideways.
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Looks like pictures shows up correct when i opened it. I for got to add that I could "hear" the blower motor relay sound like it was working when I changed fan speeds.
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The only concern with the blower relay is whether the low speed points are burned (usually, this isn't a problem). Burned low speed points will produce lower voltage readings at the motor than when the relay is temporarily bypassed using a jumper. Hence, that extra step. Bottom line, I think, is a bad blower motor, but now you have a way of checking the relay, too. Let me know how it turns out.
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How about my mystery plug?
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I tried resizing the image to get a closer view of the housing, but there's not sufficient resolution to see details. The housing hints at being cobbled to add a 2-speed resistor. I don't recognize its intended purpose or recall ever seeing that configuration. Perhaps one of the other fellas can offer some insight. Open a pole: 1) Factory, 2) Aftermarket.
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I think I figured it out I believe it's for a suburban rear air setup.
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That could be - strictly for use with rear heater, not A/C. Driver had control over the rear heater fan through an accessory switch mounted next to the ashtray.
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Your correct extra plug is for rear heat. Problem turns out that the blower motor relay was bad. Thanks for the help BD