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Blower fan fuse blows

Tiny
FRUGAL REPAIR GUY
  • MEMBER
  • 1989 CHEVROLET ASTRO
  • 6 CYL
  • 2WD
  • AUTOMATIC
  • 440,000 MILES
1989 chevy astro blower fan fuse blows but only when engine is running. Fan works fine with ignition on and engine not running.
Saturday, January 15th, 2011 AT 5:39 PM

8 Replies

Tiny
JDL
  • MECHANIC
  • 16,098 POSTS
If you have the hvac control on ac or blend, the ac compressor comes into play, engine running. Key on engine not running, the fan will run but no heat or ac.
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Saturday, January 15th, 2011 AT 6:00 PM
Tiny
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HVAC control in on heater, heat setting on high. With ignition on and engine not running, fan runs on all three settings. Start engine, turn fan on, fuse blows.
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Saturday, January 15th, 2011 AT 6:08 PM
Tiny
JDL
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I'd have to unplug blower motor and compressor, one at a time, see if fuse still blows? You can do an amp draw test on the blower motor, key on and engine running. Without doing some testing, I don't what is going on? Most people don't like testing, that is up to you.
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Saturday, January 15th, 2011 AT 6:38 PM
Tiny
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JDL, I am ok with testing. I did run run an ohm meter across the blower fuse (battery unhooked) to see what the resistance values were on the switch circuit to see if it was bad. Results of 3.5, 5 and 50 ohms were all higher than the 0.6 ohm minimum that would blow the 20 amp fuse. I=E/R I=20A, E=12v. So switch circuit seems to be ok. Will try unplugging compressor but not sure why that would be related. Will let you know. It is just strange that it only blows the fuse when engine running. Thanks.
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Saturday, January 15th, 2011 AT 6:49 PM
Tiny
JDL
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I understand your point. I don't understand either, unless your compressor is kicking on for some reason.
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Saturday, January 15th, 2011 AT 7:12 PM
Tiny
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Have tested with compressor unhooked as well as blower unhooked and fuse still blows. So it does not look like it is the blower itself so doing an amp draw test on motor would not prove anything. I am thinking is is either the resistor block or the relay or my test of the switch circuit is not correct. If you know how to test these let me know. Thanks again for your help.
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Saturday, January 15th, 2011 AT 7:22 PM
Tiny
JDL
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The diagram I posted, you click on the diagram to enlarge. You can check amp draw on any of the those circuits. You can break the components down into individual circuits and test. Something about the amp draw is changing with engine running, don't know where the problem is located, at the moment?
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Saturday, January 15th, 2011 AT 7:42 PM
Tiny
JDL
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Just a thought, maybe the engine vibration is causing a short to ground, where at key on, it doesn't ground. You could use a testlite in place of fuse, engine running, unplug hvac components one at a time, see if you can get the lite to go out. Maybe the testlite will control the load enough not to burn anything? Wiring connector or wiring itself?
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Sunday, January 16th, 2011 AT 5:04 PM

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