| Testing the dash a/c-heater fan [message #336771] |
Wed, 05 September 2018 20:00  |
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JShot
Messages: 485
Registered: October 2006
Location: NW Ohio
Karma: 0
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Is there a quick, down and dirty way to test the dash fan HIGH speed (only) WITHOUT starting the engine? Ours works fine on low and medium, but when going to high, the fuse blows. We have NO delay relay, a new high speed relay, and have checked the wiring per Emery's great write up regarding this.
John
John Shotwell
Ridgeville Corners, OH
78 Royale Center Kitchen
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| Re: Testing the dash a/c-heater fan [message #336783 is a reply to message #336771] |
Thu, 06 September 2018 01:50  |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
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Senior Member |
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What size fuse are you blowing?
Disconnect the power wire at the fan. Now start the vehicle and select the high speed fan. If the fuse still blows, your problem is NOT the fan. It is a short or a wiring error. If the fuse does not blow, suspect the fan motor or too small of a fuse.
You do know that the power source for the high speed only goes on the center terminal of the isolator.
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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| Re: [GMCnet] Testing the dash a/c-heater fan [message #336796 is a reply to message #336795] |
Thu, 06 September 2018 19:12 |
Will Albers
Messages: 183
Registered: November 2017
Location: Detroit MI (Belleville)
Karma: 2
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Check the wire gauge to the fan. My PO installed a weaker gauge than needed
and it would get very warm. Easy fix. Same goes for the ground cable.
On Thu, Sep 6, 2018, 6:46 PM Emery Stora via Gmclist <
gmclist@list.gmcnet.org> wrote:
> As the motors get older the bearings get stiffer and dry out they
> sometimes draw more amps especially to start turning. You might try
> stepping up to a 20 amp fuse.
>
> Emery Stora
> 77 Kingsley
> Frederick, CO
>
>> On Sep 6, 2018, at 3:22 PM, John Shotwell wrote:
>>
>> Goes from the HS fan relay, through a 15a fuse, to the alt output (or
> visa versa). You're gonna tell me the fuse isn't big enough...
>> --
>> John Shotwell
>> Ridgeville Corners, OH
>> 78 Royale Center Kitchen
>> Web Site: GMCmhRegistry.com
>> Email: john at gmcmhregistry dot com
>>
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1978 Palm Beach.
Detroit Michigan
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| Re: Testing the dash a/c-heater fan [message #336797 is a reply to message #336794] |
Fri, 07 September 2018 00:23 |
roy1
Messages: 2126
Registered: July 2004
Location: Minden nevada
Karma: 6
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Senior Member |
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If the motor is dragging because of dry bearings I would replace the motor or at least add oil to the bearings .
Roy Keen
Minden,NV
76 X Glenbrook
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| Re: Testing the dash a/c-heater fan [message #336798 is a reply to message #336794] |
Fri, 07 September 2018 00:26 |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
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I just looked on the wiring diagram for a 1978 Transmode. It does not show a fuse there at all. Instead it shows a #18 green fusible link. I am not sure if it is the same for all years as I only checked this one.
A #18 fusible link will definitely carry more than 15 amps. On mine I have a 30 amp fuse inline. The heater / AC fuse which runs all of the other slower speeds is 25 amp.
I suggest that you try at least a 25 amp or better yet a 30 amp fuse.
I also just checked a 1975 wiring diagram and it showed the same fusible link.
Ken B.
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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| Re: [GMCnet] Testing the dash a/c-heater fan [message #336802 is a reply to message #336797] |
Fri, 07 September 2018 07:32 |
powwerjon
Messages: 849
Registered: March 2013
Karma: -2
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You cannot oil the bearings in the fan motors. They were a bronze oil impregnated bearing when new and adding oil will only be on the bearing surface and will not last for very long. Went thru this issue a number of year back with several coaches that we owned, the high current load caused by the increased bearing friction caused a number of the AR109 relay failures.
The replacement blower motor is available from the Big Box autoparts stores at a very reasonable price. If your going to take it out, replace it!
AutoZone:
NAPA:
O’Reilly Auto Parts:
or
http://tinyurl.com/yc3mc6wk
You might also be able to find it at a non chain local store, also available on Amazon at higher pricing.
J.R. Wright
GMC Great Laker MHC
GMCGL Tech Editor
GMC Eastern States Charter Member
GMCMI
78 GMC Buskirk 30’ Stretch
75 GMC Avion (Under Reconstruction)
Michigan
> On Sep 7, 2018, at 1:23 AM, roy keen wrote:
>
> If the motor is dragging because of dry bearings I would replace the motor or at least add oil to the bearings .
> --
> Roy Keen
> Minden,NV
> 76 X Glenbrook
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