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Old 09-08-2010, 07:28 PM
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heater fan only blows on low

I have an 86 chevy 4door and slowly replacing everything in it and now on the inside i have found that when you turn the selector to anything but off the fan kicks on but only on low and i cant chage it at all. Everything works goin from defrost to floor to ac to heat but no fan speed adjustment. I have searched for this before posting a new thread but all i have found is if its stuck on high then its the resistor under the hood. What causes it to be stuck on low? Thanks for the help. Oh by the way its a new motor and resistor the guy before me tried those things and claims its a new heat/ac control panel all together and cables from lmc with a new reostat i think he called it on the fan speed adjuster but still dont work. Thanks again.
Matt

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Old 09-08-2010, 10:47 PM
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I think it has to be either the fan switch itself, or it's wire incorrectly. If it was anything else, it would run only on high.
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Old 09-09-2010, 12:27 PM
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Follow the fan wires out to the firewall, on it you will find a small relay type box, change this fan control resistor and your fan problems are over.

You can pickup from Rock Auto for about $8 - 10 bucks.

First picture is W/O air, second is With air.

Called a blower fan resistor.
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Old 09-09-2010, 01:40 PM
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"Oh by the way its a new motor and resistor the guy before me tried those things and claims its a new heat/ac control panel all together and cables from lmc with a new reostat i think he called it on the fan speed "

If everythings new, is must be how it's wired or the resistor is defective.
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Old 09-12-2010, 06:32 PM
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okay ive changed the resister on the engine side of the firewall and the switch and ran a hot wire to the fan and it fired up fine but still no different speed setings. How hard would it be to run wires from the switch to the resistor outside the truck back to the fan? I do metal fabricating and barely know how to change a lightbulb much less run wires haha. Thanks.
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Old 09-12-2010, 07:59 PM
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I think it must be wired wrong. Can you pull the connector off the back of the switch and try running power to the orange wire (full on), the lt. blue wire (medium I think), and the yellow wire (low I think) 1 at a time and see what happens. The brown at the switch is should be power with ignition on.
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Old 09-13-2010, 05:14 AM
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The idea of pulling the connector off the switch and manually connecting wires will determine if the switch is bad. If you can't get enough slack to reach thje connector from under the dash, you might have to pull the outer bezel off the instrument panel. There are a lot of screws holding it on (about 12-14), but once you take them out, and also take off the radio knobs, it just pulls off. With that removed you can see the heater controls, including the plug on the back of the fan switch. The fan switch can be replaced separately from the rest of the heater controls.

If the truck has A/C you will find at least one extra orange wire on the switch. That wire is used to put the fan on high when the A/C control is to max/recirculate. With A/C there is also a separate 30 amp inline fuse under the hood. That fuse only affects high speed.

Bruce
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Old 11-08-2010, 04:57 PM
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Found the problem......ground wire near the resistor thing in the engine compartment wasnt bolted to the firewall. I know this thread is old but might help someone else.
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Old 11-08-2010, 10:53 PM
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Thanks for the clue - I should have thought about the ground wire myself. The resister shown looks identical to the one in my Volvo, but I am supposed to have 4 speeds, not three (Delco-style one-wire fan motor). 2 and 3 work, 1 and 4 do not. I have tried both a different switch and two different resisters, but did not think of the ground. Is it possible I'm getting a false ground through one of the non-working positions? I sort of remember that 1 (Low) used to work, but 4 (High) never has.
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Old 11-09-2010, 05:30 AM
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I hope someone can help you it was just my lucky day to see a wire dangling and so i had a buddy of mine put a meter on it and when i went to high fan speed the wire made the tester light up......we grounded it and bam it worked. I have no electrical background and dont have any clue what im doin with it except car stereos so im really sorry i cant help you any but maybe someone is still keeping an eye on this thread. Goodluck.
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