Testing the dash a/c-heater fan

[JShot]

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
Web Site: GMCmhRegistry.com
Email: john at gmcmhregistry dot com

 

[john r. lebetski]

Put an Ammeter in series with a hot patch wire from battery.
--
John Lebetski
Woodstock, IL
77 Eleganza II

 

[Ken B]

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

 

[JShot]

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

 

[emerystora]

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

>
> 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
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org

 

[Will Albers]

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 <

> 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
>

> >
> > 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
> >
> > _______________________________________________
> > GMCnet mailing list
> > Unsubscribe or Change List Options:
> > http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>

 

[roy keen]

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

 

[Ken B]

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

 

[powwerjon]

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: https://www.autozone.com/cooling-heating-and-climate-control/a-c-heater-blower-motor/vdo-a-c-heater-blower-motor/141515_434469_6648_6774?&searchText=PM102

NAPA: https://www.napaonline.com/en/p/BK_6551039?interchange=1

O’Reilly Auto Parts: https://www.oreillyauto.com/detail/b/murray-climate-control-5217/lighting---electrical-16777/motors---actuators-25143/blower-motor-12457/0da7cd2eedaa/murray-climate-control-blower-motor/pm102/4781787?q=pm102&pos=0
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

>
> 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