Home » Public Forums » GMCnet » [GMCnet] No hot air from dash heat vents
| [GMCnet] No hot air from dash heat vents [message #147831] |
Wed, 26 October 2011 05:56  |
kincaid76royale
Messages: 71
Registered: February 2005
Karma: 0
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Member |
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Hi All:
We have a 76 Royale RB. I have replaced the heater core and since then I cannot get any heat in the cabin.
At first I wasn't getting any hot water circulation through the heater core, then following the suggestion of Jim Kanomata's mechanic, Alonzo, I added a shut off valve in the hose to the hot water heater heat exchanger. Now I have 190* hot water through the heater core. The fan runs and I can hear/see the vacuum actuators work as I move the control levers BUT only cold air comes out of the dash vents. Is there a combination of settings that I am missing?
Jack Kincaid, Castro Valley, CA
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| Re: [GMCnet] No hot air from dash heat vents [message #147833 is a reply to message #147831] |
Wed, 26 October 2011 07:17  |
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Matt Colie
Messages: 8547
Registered: March 2007
Location: S.E. Michigan
Karma: 7
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Senior Member |
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| kincaid76royale wrote on Wed, 26 October 2011 06:56 |
Hi All:
We have a 76 Royale RB. I have replaced the heater core and since then I cannot get any heat in the cabin.
At first I wasn't getting any hot water circulation through the heater core, then following the suggestion of Jim Kanomata's mechanic, Alonzo, I added a shut off valve in the hose to the hot water heater heat exchanger. Now I have 190* hot water through the heater core. The fan runs and I can hear/see the vacuum actuators work as I move the control levers BUT only cold air comes out of the dash vents. Is there a combination of settings that I am missing?
Jack Kincaid, Castro Valley, CA
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Jack,
If it ever worked, start looking for where a little vacuum hose fell off a door control. It any one becomes disconnected, cracked or even just too loose, the operating vacuum won't pull the doors where they need to go.
I had the diaphragm go bad in the heater control valve, and that leak was bad enough that nothing else worked at all.
I would love to tell you more, but GMC HVACs are so strange and perverse that I have no idea how mine worked until KenH. took the stage in DuQuoin. Now, I know that it makes less sense that I thought it might.
Matt
Matt & Mary Colie - Chaumière -'73 Glacier 23 - Members GMCMI, GMCGL, GMCES
Electronically Controlled Quiet Engine Cooling Fan with OE Rear Drum Brakes with Applied Control Arms
SE Michigan - Near DTW - Twixt A2 and Detroit
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| Re: [GMCnet] No hot air from dash heat vents [message #147834 is a reply to message #147831] |
Wed, 26 October 2011 07:33 |
Ken Henderson
Messages: 8726
Registered: March 2004
Location: Americus, GA
Karma: 9
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Senior Member |
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Jack,
If you haven't studied "Separating Hot from Cold", by Zay Brand, available
at http://gmcws.org/Tech/air_conditioning/air_conditing.html, you need to do
so.
In that document you'll see that if the heat door, operated by the
temperature control cable, connected at the driver's side of the under-hood
HVAC box, is in the COOL position, NO heat will be produced because there's
no airflow through the heater core.
Ken H.
Americus, GA
'76 X-Birchaven w/Cad500/Howell EFI+ & EBL
www.gmcwipersetc.com
On Wed, Oct 26, 2011 at 6:56 AM, Jack Kincaid Castro valley, CA <
kincaid76royale@comcast.net> wrote:
> Hi All:
>
> We have a 76 Royale RB. I have replaced the heater core and since then I
> cannot get any heat in the cabin.
>
> At first I wasn't getting any hot water circulation through the heater
> core, then following the suggestion of Jim Kanomata's mechanic, Alonzo, I
> added a shut off valve in the hose to the hot water heater heat exchanger.
> Now I have 190* hot water through the heater core. The fan runs and I can
> hear/see the vacuum actuators work as I move the control levers BUT only
> cold air comes out of the dash vents. Is there a combination of settings
> that I am missing?
>
>
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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] No hot air from dash heat vents [message #147846 is a reply to message #147834] |
Wed, 26 October 2011 09:49 |
James Hupy
Messages: 6806
Registered: May 2010
Karma: -62
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Senior Member |
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The heat/defrost/cooling non system in the earlier GMCs is well known to
function poorly particularly in the cooling mode. There is however, one
vacuum motor, located inside the dash which has two small rigid vacuum lines
attatched on opposite sides of the diaphram. It is supposed to be operated
by the proportional heat/cool slide control cable, ant it works when the
cable rotates a multi layer rotary vacuum distributor. Those things are
known to leak and the vacuum does not get to the diaphram in the vacuum
motor. The cable moves, the rotary valve moves, but the air door in the
heater does not. I chased one of those non functioning vacuum motors for a
couple of years one day until I realized that there are two vacuum lines
going to the vacuum motor, not one. You can kinda see it if you take out the
four screws that hold your ride height valves to the dash and pull the whole
module out far enough to look behind it. Getting your hand on it is a
challenge, but it can be done. Makes me so impatient that I am tempted to
take a sawsall to that lousy plastic dash and cut me a hole. Then when guys
would ask, "Why is that big hole in your dash? I can answer, "The Da$% thing
made me mad!. If you have the dash bezel, heater controls, and radio out,
you can access it that way also. And people wonder why there is conflicts
between engineers and technicians. One huge example.
Jim Hupy
Salem, OR
78 GMC Royale 403
On Wed, Oct 26, 2011 at 5:33 AM, Ken Henderson <hend4800@bellsouth.net>wrote:
> Jack,
>
> If you haven't studied "Separating Hot from Cold", by Zay Brand, available
> at http://gmcws.org/Tech/air_conditioning/air_conditing.html, you need to
> do
> so.
>
> In that document you'll see that if the heat door, operated by the
> temperature control cable, connected at the driver's side of the under-hood
> HVAC box, is in the COOL position, NO heat will be produced because there's
> no airflow through the heater core.
>
> Ken H.
> Americus, GA
> '76 X-Birchaven w/Cad500/Howell EFI+ & EBL
> www.gmcwipersetc.com
>
>
>
> On Wed, Oct 26, 2011 at 6:56 AM, Jack Kincaid Castro valley, CA <
> kincaid76royale@comcast.net> wrote:
>
> > Hi All:
> >
> > We have a 76 Royale RB. I have replaced the heater core and since then I
> > cannot get any heat in the cabin.
> >
> > At first I wasn't getting any hot water circulation through the heater
> > core, then following the suggestion of Jim Kanomata's mechanic, Alonzo, I
> > added a shut off valve in the hose to the hot water heater heat
> exchanger.
> > Now I have 190* hot water through the heater core. The fan runs and I can
> > hear/see the vacuum actuators work as I move the control levers BUT only
> > cold air comes out of the dash vents. Is there a combination of settings
> > that I am missing?
> >
> >
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
>
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| Re: [GMCnet] No hot air from dash heat vents [message #147910 is a reply to message #147846] |
Thu, 27 October 2011 05:49 |
kincaid76royale
Messages: 71
Registered: February 2005
Karma: 0
|
Member |
|
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Hi All:
Thanks for your replies. This thing is driving me crazy.
Zay's booklet has almost nothing about 1976's. nor does the original
Maintenance Manuals (2).
There seem to be only two doors in the heater/air conditioner "box". The
upper one, operated by a cable on the drivers side, appears to move freely
(Kroil) and the vacuum actuator for the lower one appears to work only when
the fan is in the HI position.
I'll look under the dash for the "secret" vacuum motor with two lines.
Thanks again,
Jack Kincaid
Castro Valley, CA
----- Original Message -----
From: "James Hupy" <jamesh1296@gmail.com>
To: <gmclist@temp.gmcnet.org>
Sent: Wednesday, October 26, 2011 7:49 AM
Subject: Re: [GMCnet] No hot air from dash heat vents
> The heat/defrost/cooling non system in the earlier GMCs is well known to
> function poorly particularly in the cooling mode. There is however, one
> vacuum motor, located inside the dash which has two small rigid vacuum
> lines
> attatched on opposite sides of the diaphram. It is supposed to be operated
> by the proportional heat/cool slide control cable, ant it works when the
> cable rotates a multi layer rotary vacuum distributor. Those things are
> known to leak and the vacuum does not get to the diaphram in the vacuum
> motor. The cable moves, the rotary valve moves, but the air door in the
> heater does not. I chased one of those non functioning vacuum motors for a
> couple of years one day until I realized that there are two vacuum lines
> going to the vacuum motor, not one. You can kinda see it if you take out
> the
> four screws that hold your ride height valves to the dash and pull the
> whole
> module out far enough to look behind it. Getting your hand on it is a
> challenge, but it can be done. Makes me so impatient that I am tempted to
> take a sawsall to that lousy plastic dash and cut me a hole. Then when
> guys
> would ask, "Why is that big hole in your dash? I can answer, "The Da$%
> thing
> made me mad!. If you have the dash bezel, heater controls, and radio out,
> you can access it that way also. And people wonder why there is conflicts
> between engineers and technicians. One huge example.
> Jim Hupy
> Salem, OR
> 78 GMC Royale 403
>
> On Wed, Oct 26, 2011 at 5:33 AM, Ken Henderson
> <hend4800@bellsouth.net>wrote:
>
>> Jack,
>>
>> If you haven't studied "Separating Hot from Cold", by Zay Brand,
>> available
>> at http://gmcws.org/Tech/air_conditioning/air_conditing.html, you need to
>> do
>> so.
>>
>> In that document you'll see that if the heat door, operated by the
>> temperature control cable, connected at the driver's side of the
>> under-hood
>> HVAC box, is in the COOL position, NO heat will be produced because
>> there's
>> no airflow through the heater core.
>>
>> Ken H.
>> Americus, GA
>> '76 X-Birchaven w/Cad500/Howell EFI+ & EBL
>> www.gmcwipersetc.com
>>
>>
>>
>> On Wed, Oct 26, 2011 at 6:56 AM, Jack Kincaid Castro valley, CA <
>> kincaid76royale@comcast.net> wrote:
>>
>> > Hi All:
>> >
>> > We have a 76 Royale RB. I have replaced the heater core and since then
>> > I
>> > cannot get any heat in the cabin.
>> >
>> > At first I wasn't getting any hot water circulation through the heater
>> > core, then following the suggestion of Jim Kanomata's mechanic, Alonzo,
>> > I
>> > added a shut off valve in the hose to the hot water heater heat
>> exchanger.
>> > Now I have 190* hot water through the heater core. The fan runs and I
>> > can
>> > hear/see the vacuum actuators work as I move the control levers BUT
>> > only
>> > cold air comes out of the dash vents. Is there a combination of
>> > settings
>> > that I am missing?
>> >
>> >
>> _______________________________________________
>> GMCnet mailing list
>> Unsubscribe or Change List Options:
>> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
>>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
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| Re: [GMCnet] No hot air from dash heat vents [message #147925 is a reply to message #147910] |
Thu, 27 October 2011 09:50 |
Mr ERFisher
Messages: 7117
Registered: August 2005
Karma: 2
|
Senior Member |
|
|
Hi Jack
did you read through these ?
http://gmcmotorhome.info/heat.html#CONFIG
is your fan running?
gene
On Thu, Oct 27, 2011 at 3:49 AM, Jack Kincaid Castro valley, CA <
kincaid76royale@comcast.net> wrote:
> Hi All:
>
> Thanks for your replies. This thing is driving me crazy.
>
> Zay's booklet has almost nothing about 1976's. nor does the original
> Maintenance Manuals (2).
>
> There seem to be only two doors in the heater/air conditioner "box". The
> upper one, operated by a cable on the drivers side, appears to move freely
> (Kroil) and the vacuum actuator for the lower one appears to work only when
> the fan is in the HI position.
>
> I'll look under the dash for the "secret" vacuum motor with two lines.
>
> Thanks again,
>
> Jack Kincaid
> Castro Valley, CA
>
> ----- Original Message -----
> From: "James Hupy" <jamesh1296@gmail.com>
> To: <gmclist@temp.gmcnet.org>
> Sent: Wednesday, October 26, 2011 7:49 AM
> Subject: Re: [GMCnet] No hot air from dash heat vents
>
>
> > The heat/defrost/cooling non system in the earlier GMCs is well known to
> > function poorly particularly in the cooling mode. There is however, one
> > vacuum motor, located inside the dash which has two small rigid vacuum
> > lines
> > attatched on opposite sides of the diaphram. It is supposed to be
> operated
> > by the proportional heat/cool slide control cable, ant it works when the
> > cable rotates a multi layer rotary vacuum distributor. Those things are
> > known to leak and the vacuum does not get to the diaphram in the vacuum
> > motor. The cable moves, the rotary valve moves, but the air door in the
> > heater does not. I chased one of those non functioning vacuum motors for
> a
> > couple of years one day until I realized that there are two vacuum lines
> > going to the vacuum motor, not one. You can kinda see it if you take out
> > the
> > four screws that hold your ride height valves to the dash and pull the
> > whole
> > module out far enough to look behind it. Getting your hand on it is a
> > challenge, but it can be done. Makes me so impatient that I am tempted to
> > take a sawsall to that lousy plastic dash and cut me a hole. Then when
> > guys
> > would ask, "Why is that big hole in your dash? I can answer, "The Da$%
> > thing
> > made me mad!. If you have the dash bezel, heater controls, and radio out,
> > you can access it that way also. And people wonder why there is conflicts
> > between engineers and technicians. One huge example.
> > Jim Hupy
> > Salem, OR
> > 78 GMC Royale 403
> >
> > On Wed, Oct 26, 2011 at 5:33 AM, Ken Henderson
> > <hend4800@bellsouth.net>wrote:
> >
> >> Jack,
> >>
> >> If you haven't studied "Separating Hot from Cold", by Zay Brand,
> >> available
> >> at http://gmcws.org/Tech/air_conditioning/air_conditing.html, you need
> to
> >> do
> >> so.
> >>
> >> In that document you'll see that if the heat door, operated by the
> >> temperature control cable, connected at the driver's side of the
> >> under-hood
> >> HVAC box, is in the COOL position, NO heat will be produced because
> >> there's
> >> no airflow through the heater core.
> >>
> >> Ken H.
> >> Americus, GA
> >> '76 X-Birchaven w/Cad500/Howell EFI+ & EBL
> >> www.gmcwipersetc.com
> >>
> >>
> >>
> >> On Wed, Oct 26, 2011 at 6:56 AM, Jack Kincaid Castro valley, CA <
> >> kincaid76royale@comcast.net> wrote:
> >>
> >> > Hi All:
> >> >
> >> > We have a 76 Royale RB. I have replaced the heater core and since then
> >> > I
> >> > cannot get any heat in the cabin.
> >> >
> >> > At first I wasn't getting any hot water circulation through the heater
> >> > core, then following the suggestion of Jim Kanomata's mechanic,
> Alonzo,
> >> > I
> >> > added a shut off valve in the hose to the hot water heater heat
> >> exchanger.
> >> > Now I have 190* hot water through the heater core. The fan runs and I
> >> > can
> >> > hear/see the vacuum actuators work as I move the control levers BUT
> >> > only
> >> > cold air comes out of the dash vents. Is there a combination of
> >> > settings
> >> > that I am missing?
> >> >
> >> >
> >> _______________________________________________
> >> GMCnet mailing list
> >> Unsubscribe or Change List Options:
> >> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
> >>
> > _______________________________________________
> > GMCnet mailing list
> > Unsubscribe or Change List Options:
> > http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://temp.gmcnet.org/cgi-bin/mailman/listinfo/gmclist
>
--
Gene Fisher -- 74-23,77PB/ore/ca
“Give a man a fish; you have fed him for today --- give him a URL and
-------
http://gmcmotorhome.info/
Alternator Protection Cable
http://gmcmotorhome.info/APC.html
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