| [GMCnet] More Blower Woes [message #279084] |
Thu, 04 June 2015 20:28  |
Daniel DeLuca
Messages: 120
Registered: June 2014
Karma: 0
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Hello,
Just when I thought I had a ‘really’ good handle on how the blower fan functioned on my ’78 it throws me another curveball. So this spring I replaced the resistor pack and the relay on my blower fan. Tested it and had all speeds. Today took the coach out for a spin, and of course once again I had no fan. Well I think I know how everything works now so I go out there with a multimeter and figure I’ll have it sorted in about ten minutes.
Nope
Now my relay is good and my resistor pack is good, but it seems like nothing is getting voltage from the dash unit. No voltage through resistor pack and no click of the relay. Of course I check the fuse and its okay. So, is it possible my control unit went south? I am really tempted just to hotwire it to some middle speed and be done with it. The only thing I noticed is that the little 5A fuse labled AUX is blown, what does that power?
Dan
78 Eleganza
NJ
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| Re: [GMCnet] More Blower Woes [message #279085 is a reply to message #279084] |
Thu, 04 June 2015 21:05  |
habbyguy
Messages: 896
Registered: May 2012
Location: Mesa, AZ
Karma: 3
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My coach had the same problem when I bought it. Turned out to be a bad connection on the back of the fusebox. I'd suggest seeing if you can just bring 12V over to the relay via a jumper wire, just to rule out any other problems.
Mark Hickey
Mesa, AZ
1978 Royale Center Kitchen
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| Re: [GMCnet] More Blower Woes [message #279087 is a reply to message #279084] |
Thu, 04 June 2015 21:28 |
JohnL455
Messages: 4447
Registered: October 2006
Location: Woodstock, IL
Karma: 12
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Senior Member |
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Double check the connections at the resistor, high relay, delay relay (or patch around it no cutting required) those connections can look good and be bad. Spray with Caig D5. Last week all speeds went out on my 98 Tahoe. Complete new GM dash control about a year ago as fan switch bad. Traced problem to some sort of coating on the fan switch pins Like an enamal on motor windings. This is a newer design but also check connector on dash fan switch.
John Lebetski
Woodstock, IL
77 Eleganza II
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| Re: [GMCnet] More Blower Woes [message #279091 is a reply to message #279084] |
Thu, 04 June 2015 22:46 |
Bob de Kruyff
Messages: 4260
Registered: January 2004
Location: Chandler, AZ
Karma: 1
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Senior Member |
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Daniel DeLuca wrote on Thu, 04 June 2015 19:28Hello,
Just when I thought I had a 'really' good handle on how the blower fan functioned on my '78 it throws me another curveball. So this spring I replaced the resistor pack and the relay on my blower fan. Tested it and had all speeds. Today took the coach out for a spin, and of course once again I had no fan. Well I think I know how everything works now so I go out there with a multimeter and figure I'll have it sorted in about ten minutes.
Nope
Now my relay is good and my resistor pack is good, but it seems like nothing is getting voltage from the dash unit. No voltage through resistor pack and no click of the relay. Of course I check the fuse and its okay. So, is it possible my control unit went south? I am really tempted just to hotwire it to some middle speed and be done with it. The only thing I noticed is that the little 5A fuse labled AUX is blown, what does that power?
Dan
78 Eleganza
NJ
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The little fuse is for the instrument panel lights. How did you check the other fuse? Many times those glass fuses are fine but not making connection in the clips. I would pop it out and then back in. It's possible that the fan switch is bad. One way to check is to put the control lever in MAX which by passes the switch and should result in high blower speed. Also the connector right at the motor is troublesome--I would unplug and plug back in.
Bob de Kruyff
78 Eleganza
Chandler, AZ
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| Re: [GMCnet] More Blower Woes [message #279092 is a reply to message #279091] |
Thu, 04 June 2015 22:56 |
Bullitthead
Messages: 1411
Registered: November 2013
Karma: 5
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Senior Member |
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Frequently my blower refuses to operate until I touch the HVAC fuse. Seems that the spring clips that hold the fuse develop a surface corrosion after 40 years. Careful scraping or using a 22 caliber rifle brush on those contacts may solve the problem for a few more years.
Terry Kelpien
ASE Master Technician
73 Glacier 260
Smithfield, Va.
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| Re: [GMCnet] More Blower Woes [message #279136 is a reply to message #279084] |
Fri, 05 June 2015 12:20 |
C Boyd
Messages: 2629
Registered: April 2006
Karma: 18
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Senior Member |
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Sir the hi speed works only with engine running. The other speeds are thru the resistor. They have separate fuses. The only thing in common is the ground wire on the fan motor and can become loose or dirty. If the screw will not tighten, use a different fan mounting screw.
http://www.gmcmhphotos.com/photos/member-galleries/p42831-dsc03822-a.html
quote title=Daniel DeLuca wrote on Thu, 04 June 2015 21:28]Hello,
Just when I thought I had a 'really' good handle on how the blower fan functioned on my '78 it throws me another curveball. So this spring I replaced the resistor pack and the relay on my blower fan. Tested it and had all speeds. Today took the coach out for a spin, and of course once again I had no fan. Well I think I know how everything works now so I go out there with a multimeter and figure I'll have it sorted in about ten minutes.
Nope
Now my relay is good and my resistor pack is good, but it seems like nothing is getting voltage from the dash unit. No voltage through resistor pack and no click of the relay. Of course I check the fuse and its okay. So, is it possible my control unit went south? I am really tempted just to hotwire it to some middle speed and be done with it. The only thing I noticed is that the little 5A fuse labled AUX is blown, what does that power?
Dan
78 Eleganza
NJ
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[/quote]
C. Boyd
76 Crestmont
East Tennessee
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| Re: [GMCnet] More Blower Woes [message #279169 is a reply to message #279084] |
Fri, 05 June 2015 19:49 |
JohnL455
Messages: 4447
Registered: October 2006
Location: Woodstock, IL
Karma: 12
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Senior Member |
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Sounds like you fixed it Dan. It's always something "stupid" causing the problem. I hate those odd fuse box layouts as well.
John Lebetski
Woodstock, IL
77 Eleganza II
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| Re: [GMCnet] More Blower Woes [message #279175 is a reply to message #279173] |
Fri, 05 June 2015 22:13 |
Ken Henderson
Messages: 8726
Registered: March 2004
Location: Americus, GA
Karma: 9
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Senior Member |
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To clarify the yellow wire comment: One of the wires to the resistor pack
at the left (driver's) side of the HVAC box under the hood is yellow.
That's the power for the "always ON" function. Cutting that wire (or more
appropriately, bending the connector contact over) disables that function
without affecting anything else. A lot of people then use that as a
readily accessible AUX power source.
Ken H.
Americus, GA
'76 X-Birchaven w/Cad500/Howell EFI & EBL,
Manny Brakes & 1-Ton, etc., etc.
www.gmcwipersetc.com
On Fri, Jun 5, 2015 at 10:45 PM, A. wrote:
> 78 models don't have "off". It came from the factory with 4 speeds. If the
> key is on, and there are no wiring/connection problems, the fan is turning.
>
Unless someone has cut the yellow wire to make the "Lo" position into "Off".
> --
>
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Ken Henderson
Americus, GA
www.gmcwipersetc.com
Large Wiring Diagrams
76 X-Birchaven
76 X-Palm Beach
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| Re: [GMCnet] More Blower Woes [message #279181 is a reply to message #279084] |
Fri, 05 June 2015 23:39 |
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John Heslinga
Messages: 632
Registered: February 2011
Location: Edmonton, Alberta, Canada
Karma: 4
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Senior Member |
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Here are some pictures of the function lever elctrical wiper switch. It is from a early model GMC, however the 78 Wiring Diagram showes it to be about the same. This particular one was badly burned due to many corroded connectors. No discriptions at this time but they will be better explained at a later date. (and more pictures) I put them here now just to show that this switch and it's connectors also need to be included in the HVAC electrical diagnostics. It is not from My Coach
http://www.gmcmhphotos.com/photos/g6797-hvac-dash-control.html
John and Cathie Heslinga
1974 Canyonlands 260
455, Manny tranny and 1 ton, 3:70 LS,
Red Seal Journeyman, DTE, BEd. MEd.
Edmonton, Alberta
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| Re: [GMCnet] More Blower Woes [message #279189 is a reply to message #279175] |
Sat, 06 June 2015 03:29 |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
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Senior Member |
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I use that disconnected yellow lead to power my Aux vacuum pump.
Ken Henderson wrote on Fri, 05 June 2015 22:13To clarify the yellow wire comment: One of the wires to the resistor pack
at the left (driver's) side of the HVAC box under the hood is yellow.
That's the power for the "always ON" function. Cutting that wire (or more
appropriately, bending the connector contact over) disables that function
without affecting anything else. A lot of people then use that as a
readily accessible AUX power source.
Ken H.
Americus, GA
'76 X-Birchaven w/Cad500/Howell EFI & EBL,
Manny Brakes & 1-Ton, etc., etc.
www.gmcwipersetc.com
On Fri, Jun 5, 2015 at 10:45 PM, A. wrote:
> 78 models don't have "off". It came from the factory with 4 speeds. If the
> key is on, and there are no wiring/connection problems, the fan is turning.
>
Unless someone has cut the yellow wire to make the "Lo" position into "Off".
> --
>
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Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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