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defrost not working well

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by schwank, Dec 7, 2001.

  1. schwank

    schwank Registered Member

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    I have a 91 K5 that I hit Mt. Hood in frequently. My only problem with this quality rig is the defroster. The fan only works in 2 speeds, even with a 4 speed switch. Given my experience with various GM autos, I definitely think the high speed is nowhere near correct, and I have some pretty serious fogging problems on the front window in cold/wet weather.

    Any feedback as to how common and/or easy this would be to repair? Just got this guy, and it is a kick-ass truck. Where is the fan located, are there high speed aftermarket replacements available, and what's the best way to go forward.

    Question 2: Computer chips. Any of you folks with newer rides reccommend a replacement. I see the Superchips model advertising +21HP for only 199 bucks. Gimme some feedback!!

    thanks

    schwank
     
  2. dyeager535

    dyeager535 1 ton status Premium Member

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    Blower motor probs. Depends if you have AC or not. HUGE difference between AC and non AC trucks in the volume of air moved. Most cars are AC, fewer trucks (comparatively) are. Of course the C42 option changes that. : ) BTW, thats the HD heater option.

    4 speed switch only working on 2 speeds can be a few things. The switch on the dash itself (not common to fail) the wiring to the fan (the single straight 12v wire melts on the cars pretty often, not sure about trucks) and the resistor assembly on the heater/AC box. I don't have a wiring manual in front of me, but the blower motor, IIRC, only has 3 speed "inputs" that vintage, no matter if AC, non AC, or HD heater. Fan is on the passenger side in the engine bay. been so long since i've had AC, I can't remember where the blower motor is, but the AC assembly is a large piece of plastic that juts out from teh passenger side fenderwell. Look for a 4 prong plug, that goes to the resistor, and two wires to the blower motor. One to the fan housing (ground) and one that plugs into it with a weather resistant connector. Non AC is easy, its the small metal box on the passenger side near where the heater hoses run. Only wires in into that box are the blower motor ones.

    If you only have two speeds, its pretty darn unlikely its the motors fault. Check the resistor assembly and the wires leading to it. Seperate harness from the heater control head to the blower assembly, only non independent wire is a brown one to the heater head assembly from the fuse panel. if that wasn't geting power, IIRC, you'd have NO heater.

    As to the chips, since the trucks still ran a fairly primitive ECM at that time which was pretty comparable to the cars (which I have more experience with) I'd bet experiences with "chips" and cars that vintage would be pretty similar. Not worth anything near what a good set of headers will do for a bit more money.

    Dorian
    My tech/links page: <a target="_blank" href=http://www.dorianyeager.com/index2.html>www.dorianyeager.com/index2.html</a>
    Why insist on counting when the ring gear has the tooth counts stamped in?<P ID="edit"><FONT class="small">Edited by dyeager535 on 12/08/01 03:33 AM.</FONT></P>
     
  3. riz

    riz 3/4 ton status

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    <font color=purple> I had the same problem with mine ......... check under the dash to see if all the routing is right then get a bigger vaccume canister to help aid the defrosters ........... that's right ..........you need more vaccum to get it to work right. Especially if you have a bigger vaccum sucking cam. I did this to mine and now the window clears in no time flat ! Good luck. Remember to check everything first to see if it all works before you do that, although it wouldn't hurt at all to put in a larger vaccum canister anyway.

    L8r,
    . Riz . <a target="_blank" href=http://www.geocities.com/rizmonkey>www.geocities.com/rizmonkey</a>

    <font color=purple> BOW CHICKA BOW WOW !
     
  4. dyeager535

    dyeager535 1 ton status Premium Member

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    He probably already knows it, but just in case, vacuum doesn't control fan speed. It can redirect air, but vacuum, or lack thereof, doesn't influence how much air the fan pushes. Top slider runs off of vacuum (air, vent, defrost), the lower slider is run by cable (hot/cold, anything in between) and the switch is electrical.

    He mentioned two speeds, so even if the defrost/heater/vent vacuum operated lever was malfunctioning, velocity of the air coming out of whatever vent it was stuck on would be higher, if thefan speed was changing.

    Dorian
    My tech/links page: <a target="_blank" href=http://www.dorianyeager.com/index2.html>www.dorianyeager.com/index2.html</a>
    Why insist on counting when the ring gear has the tooth counts stamped in?
     

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