blower motor/AC/heat

A

adam metzger

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Oct 12, 2016
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when I went on the ill fated maiden voyage, I had the AC on and running. In removing all sorts of jiggery pokery from the engine that the PO
installed, I'm fairly certain that I removed some crucial unknown wire that allowed the system to work, because now it's not blowing. at all. No
heat either.

The only thing I get is a thumping sound behind the passenger side of the dash when I put on the hi setting. from what i understand, the hi setting
comes from a different system than the others? How does that work?

I'm 90% certain that one of the switches that the PO installed had something to do with the hi setting on the AC, and that's the only way I had it
running because, well....Texas.

I did notice that when I had it on yesterday while running the coach just to warm it up and keep things moving, the AC compressor got cold. so
something is working, perhaps just the blower motor?

--
1976 Palm Beach
Austin, TX
 
> when I went on the ill fated maiden voyage, I had the AC on and running. In removing all sorts of jiggery pokery from the engine that the PO
> installed, I'm fairly certain that I removed some crucial unknown wire that allowed the system to work, because now it's not blowing. at all. No
> heat either.
>
> The only thing I get is a thumping sound behind the passenger side of the dash when I put on the hi setting. from what i understand, the hi
> setting comes from a different system than the others? How does that work?
>
> I'm 90% certain that one of the switches that the PO installed had something to do with the hi setting on the AC, and that's the only way I had it
> running because, well....Texas.
>
> I did notice that when I had it on yesterday while running the coach just to warm it up and keep things moving, the AC compressor got cold. so
> something is working, perhaps just the blower motor is not?
Seems to me the only thing that can thump is the fan.

My guess is there is not enough power getting to the blower motor on any setting except high, and when it gets enough power, it beats against a rodent
nest. If the compressor is getting cold, the blower motor fuse is OK. You will probably need to take the motor out/off anyway to untangle the fodder
in the blower box.

And check the wiring diagrams at http://www.gmcmhphotos.com/photos/hvac-dash-and-blower-control/p58076-78-hvac-control.html or at
http://www.gmcmhphotos.com/photos/electrical/p50601-high-speed-dash-fan-circuit-path.html depending on which dash fan control you have
(low/medlow/med/hi or off/lo/med/high).
--
73 23' Sequoia 4 Sale
73 23' CanyonLands Parts Unit 4 Sale
Upper Alabama
"Highest price does not guarantee highest quality."
 
> > when I went on the ill fated maiden voyage, I had the AC on and running. In removing all sorts of jiggery pokery from the engine that the PO
> > installed, I'm fairly certain that I removed some crucial unknown wire that allowed the system to work, because now it's not blowing. at all. No
> > heat either.
> >
> > The only thing I get is a thumping sound behind the passenger side of the dash when I put on the hi setting. from what i understand, the hi
> > setting comes from a different system than the others? How does that work?
> >
> > I'm 90% certain that one of the switches that the PO installed had something to do with the hi setting on the AC, and that's the only way I
> > had it running because, well....Texas.
> >
> > I did notice that when I had it on yesterday while running the coach just to warm it up and keep things moving, the AC compressor got cold.
> > so something is working, perhaps just the blower motor is not?
> Seems to me the only thing that can thump is the fan.
>
> My guess is there is not enough power getting to the blower motor on any setting except high, and when it gets enough power, it beats against a
> rodent nest. If the compressor is getting cold, the blower motor fuse is OK. You will probably need to take the motor out/off anyway to untangle the
> fodder in the blower box.
>
> And check the wiring diagrams at http://www.gmcmhphotos.com/photos/hvac-dash-and-blower-control/p58076-78-hvac-control.html or at
> http://www.gmcmhphotos.com/photos/electrical/p50601-high-speed-dash-fan-circuit-path.html depending on which dash fan control you have
> (low/medlow/med/hi or off/lo/med/high).

Rodents nest? Really? That seems odd. You think it's that and not the wiring?
--
1976 Palm Beach
Austin, TX
 
> when I went on the ill fated maiden voyage, I had the AC on and running. In removing all sorts of jiggery pokery wiring from the engine that the
> PO installed, I'm fairly certain that I removed some crucial unknown wire that allowed the system to work, because now it's not blowing. at all.
> No heat either.
>
> The only thing I get is a thumping sound behind the passenger side of the dash when I put on the hi setting. from what i understand, the hi
> setting comes from a different system than the others? How does that work?
>
> I'm 90% certain that one of the switches that the PO installed had something to do with the hi setting on the AC, and that's the only way I had it
> running because, well....Texas.
>
> I did notice that when I had it on yesterday while running the coach just to warm it up and keep things moving, the AC compressor got cold. so
> something is working, perhaps just the blower motor is not?

--
1976 Palm Beach
Austin, TX
 
>

I think he is trying to catch up with JimK. :)
Matt

Answers to the post that has writing in it.

There are only three things that can "thump" in and about the right side dashboard. The fan would be my first guess, too. If the compressor is
running and you aren't getting any cool air out, then the fan would be a good place to start. It is not hard to remove and yes, little animals like
to make a home in GMCs. (I think they know that they will be around longer than Winyboxos.) If the thumps was real regular, that is almost a given.
If the thump was slow and irregular, then it might be one of the HVAC doors opening and closing as it tried to do what the control wanted and there is
a vacuum leak so it sets up an oscillation.

Good luck

Matt

--
Matt & Mary Colie - Members GMCMI, GMCGL, GMCES
'73 Glacier 23 - Still Loving OE Rear Drum Brake with Applied Control Arms
Now with both true Keyless and remote entry
SE Michigan - Twixt A2 and Detroit
 
> >
>
> I think he is trying to catch up with JimK. :)
> Matt
>
> Answers to the post that has writing in it.
>
> There are only three things that can "thump" in and about the right side dashboard. The fan would be my first guess, too. If the compressor is
> running and you aren't getting any cool air out, then the fan would be a good place to start. It is not hard to remove and yes, little animals like
> to make a home in GMCs. (I think they know that they will be around longer than Winyboxos.) If the thumps was real regular, that is almost a given.
> If the thump was slow and irregular, then it might be one of the HVAC doors opening and closing as it tried to do what the control wanted and there
> is a vacuum leak so it sets up an oscillation.
>
> Good luck
>
> Matt


The thump is a single sound, as a reaction to setting the switch to the hi setting.

--
1976 Palm Beach
Austin, TX
 
High speed position trips a relay that allows the fan to draw power directly from the alternator output. The relay is the top one on the passenger
side of the a/c - heater box.
Tom, MS II
--
1975 GMC Avion
KA4CSG
 
Adam, is your Climate Control Fan switch connected?

http://www.gmcmotorhome.com/tech/heatfan/index.html

From the 75-76 manual manual page 1-46

BLOWER SWITCH, RELAY & RESISTOR
The blower switch, blower relay and the blower
resistor must be discussed together because of their
interrelations with each other. The blower switch
located on the instrument panel regulates low,
medium and high blower speeds through a blower
resistor system. This resistor (figure 15) regulates the
amount of current fed to the blower thereby regulating
the blower speed. The blower relay (figure 20)
provides the proper connections for the low and
medium speeds through the resistor assembly and
direct battery current to the blower for high speed..

> > >
> >
> > I think he is trying to catch up with JimK. :)
> > Matt
> >
> > Answers to the post that has writing in it.
> >
> > There are only three things that can "thump" in and about the right side
> dashboard. The fan would be my first guess, too. If the compressor is
> > running and you aren't getting any cool air out, then the fan would be a
> good place to start. It is not hard to remove and yes, little animals like
> > to make a home in GMCs. (I think they know that they will be around
> longer than Winyboxos.) If the thumps was real regular, that is almost a
> given.
> > If the thump was slow and irregular, then it might be one of the HVAC
> doors opening and closing as it tried to do what the control wanted and
> there
> > is a vacuum leak so it sets up an oscillation.
> >
> > Good luck
> >
> > Matt
>
>
> The thump is a single sound, as a reaction to setting the switch to the hi
> setting.
>
> --
> 1976 Palm Beach
> Austin, TX
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>

--
Bruce Hart
1976 Palm Beach
Milliken, Co
GMC=Got More Class
 
I think the thump that you are hearing is the Fan relay that is mounted on the fire wall. The fan relay is only energized on the high setting.
--
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
 
Adam, if you hear a clunk when you turn the fan on HIGH speed, that is the
relay pulling in. Normal sound. If the engine is running, and alternator is
charging, the fan will run. If the engine is not running, but the key is
on, you will hear the relay pull in, but no fan will run.
Jim Hupy
Salem, Or
78 GMC ROYALE 403

> I think the thump that you are hearing is the Fan relay that is mounted on
> the fire wall. The fan relay is only energized on the high setting.
> --
> Ken Burton - N9KB
> 76 Palm Beach
> Hebron, Indiana
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
 
So what if the engine is running, hi setting makes the sound, but no air moves? I'll check out the blower tomorrow.
Speaking of blower, there is a small wire that looks like a ground wire, but it runs out brought a cylinder. Is this a resistor or some other sort of
connection?
--
1976 Palm Beach
Austin, TX
 
Capacitor. Dampens radio interference. If open, no fan. But, does fan run
in lower speed settings?
Jim Hupy

> So what if the engine is running, hi setting makes the sound, but no air
> moves? I'll check out the blower tomorrow.
> Speaking of blower, there is a small wire that looks like a ground wire,
> but it runs out brought a cylinder. Is this a resistor or some other sort of
> connection?
> --
> 1976 Palm Beach
> Austin, TX
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
 
> The thump is a single sound, as a reaction to setting the switch to the hi setting.
That would be the blower relay switching to high.

If no air is moving, either your fan is not turning or is clogged, or the actuators are not routing air like they are supposed to. I said if your
compressor is getting cold, the fuse has not blown. But check it anyway.

The fan/blower box can be clogged with rodent nests. http://www.gmcmhphotos.com/photos/misc/p18033.html

If none of the actuators are working, probably a vacuum clog or leak.

Here's the vacuum actuator drawing:
http://www.gmcmhphotos.com/photos/color-hvac-troubleshooting-charts/p22990-hvac-diagram-color-comp.html
--
73 23' Sequoia 4 Sale
73 23' CanyonLands Parts Unit 4 Sale
Upper Alabama
"Highest price does not guarantee highest quality."
 
The blower is grounded with a single black wire under one of its mounting
screws. That screw is threaded into the fiberglass housing. If even
slightly loose, it will disable the fan.

Put a star washer and anti-corrosion compound on it and tighten it securely
-- with a larger screen if necessary.

Ken H

> So what if the engine is running, hi setting makes the sound, but no air
> moves? I'll check out the blower tomorrow.
> Speaking of blower, there is a small wire that looks like a ground wire,
> but it runs out brought a cylinder. Is this a resistor or some other sort of
> connection?
> --
> 1976 Palm Beach
> Austin, TX
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
 
> The blower is grounded with a single black wire under one of its mounting
> screws. That screw is threaded into the fiberglass housing. If even
> slightly loose, it will disable the fan.
>
> Put a star washer and anti-corrosion compound on it and tighten it securely
> -- with a larger screen if necessary.
>
> Ken H

Colonel Sir, You beat me to that suggestion.
--
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
 
So why didn't you suggest fastening it with something besides a "screen"?

Ken H

>

> > The blower is grounded with a single black wire under one of its
mounting
> > screws. That screw is threaded into the fiberglass housing. If even
> > slightly loose, it will disable the fan.
> >
> > Put a star washer and anti-corrosion compound on it and tighten it
securely
> > -- with a larger screen if necessary.
> >
> > Ken H
>
>
>
> Colonel Sir, You beat me to that suggestion.
> --
 
> So why didn't you suggest fastening it with something besides a "screen"?
>
> Ken H

Because I thought that might be the Georgia way of spelling "screw". The Britts and Aussies spell windshield as "windscreen". So I thought maybe
something like that was going on here.

Actually, I have no room to speak when it comes to typing. I really assumed that it was a typographic error or your spell checker changed it to
"screen" for you.
--
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
 
I don't understand how anybody is successful in grounding anything to fiberglass.
--
Terry Kelpien

ASE Master Technician

73 Glacier 260

Smithfield, Va.
 
You better have another wire under the screw to the negative side of the battery or engine block or chassis or there is no ground path.
--
Terry Kelpien

ASE Master Technician

73 Glacier 260

Smithfield, Va.
 
Thanks y'all. I went out this morning and started poking around. I discovered the capacitor, and what it's for, through the schematics. I also
discovered that The capacitor ground was really loose and corroded.

Disconnected it, cleaned up the ground and the capacitor bracket with some sandpaper, screwed in tight, and it fired up!

It's ALWAYS the ground.

I did notice that the wire jacket on the capacitor wire is broken. Would it be wise to replace the whole assembly (plug, capacitor, wire)

Is this a place where good old electrical tape is acceptable?

Thank you Kens-colonel and otherwise. 😀

--
1976 Palm Beach
Austin, TX
 
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