Dash Heat

andrew

New member
Apr 28, 2011
217
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Let's take a poll: how many of you have coaches with the original dash heat in working order? Bought mine without it and haven't missed it but seeing
if it's even worth getting it working again. Super involved or easy?
--
1978 Kingsley -
Kansas City, MO
 
Like many other coaches, mine had a manual shut off valve under the hood. People install the manual shut off to make sure no heat can get to the
cabin during the summer months when you need air conditioning, not heat. I would search for a possible shut off valve. I had my coach out yesterday
and the heat was kind of nice.
--
1978 GMC Royal
Eastern Pennslyvania
1968 Chevrolet C20 396 Camper Special
1969 Chevrolet C20 Camper Special
1985 Buick Electra Park Avenue
1992 Camaro 25th Anniversary Heretage Edition Black
 
GMC's have a vacuum operated valve in the hot water line to the heater. Being 40 years old, it may have failed. Most have placed a manual valve in
this line to keep the hot water out of the heater body to assist in actually getting cooler air when using the A/C.

This is the first place to look.

Om
--
2012 Phoenix Cruiser model 2552
KA4CSG
 
> Let's take a poll: how many of you have coaches with the original dash heat in working order? Bought mine without it and haven't missed it but
> seeing if it's even worth getting it working again. Super involved or easy?

Kingsley,

As a 78, you are supposed to have the final and best HVAC. My 73 is adequate for the situations we have been exposed to, but I added a valve in the
heater line anyway. My heater valve had died long before, but I found a replacement. If you replace that valve, be sure that you know what you are
doing because, at least in my 73, that valve was vacuum to CLOSE.

One of the reasons I am sure that it opened as we crossed the Bighorn. It kind of had to, there was no vacuum left.

Matt
--
Matt & Mary Colie - '73 Glacier 23 - Members GMCMI, GMCGL, GMCES
Electronically Controlled Quiet Engine Cooling Fan
OE Rear Drum Brakes with Applied Control Arms
SE Michigan - Twixt A2 and Detroit
 
Working.

Easy to fix.

Yes, I use it.

Dolph

DE AD0LF

Wheeling, West Virginia

1977 26’ ex-PalmBeach
Howell EFI & EBL, Reaction Arms, Sullybilt Bags, Manny Transmission

“The Aluminum and Fiberglass Mistress"

>
> Let's take a poll: how many of you have coaches with the original dash heat in working order? Bought mine without it and haven't missed it but seeing
> if it's even worth getting it working again. Super involved or easy?
> --
> 1978 Kingsley -
> Kansas City, MO
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
 
My 73 Canyonlands heater, like Matt's 73, is adequate. The main thing is the defroster works. The AC though is worthless. I took the box apart,
cleaned everything, put new foam on the flap, and sealed the seams. I'm going to have work on the ducting but that's way down on the list.
--
Patti & Jerry Burt Fresno, CA.
73 Gmc 26' Canyon Lands -
77 Palm Beach
Members: FMCA - GMCMI - GMCWS - 49ers
A truly happy person is one who can enjoy the scenery on a detour.
 
My 74 Glacier was and hand me down from 3 other po's.
some one along the line disconnected all the vacuum lines to the dash controls, they sealed them by melting them closed.
This stopped any air flow through the dash vent system.
My fix was to prop the vent doors open to allow air flow.

I didn't have heat, neither did the PO before me.

The fix was to replace the cable from the dash control box to the heat/ac box under the hood where it attaches to a vent handle on the right side.

What made mine fail was the heat/ac box vent door was closed to heat, that is air could not flow through to the heat core to heat the air.
The cable attaches by a screw to the heat control in the dash. This attachment is plastic, and mine was broken.
With this broken, you could move the lever to the heat side of the control and only the entire cable moves, not the wire inside which would have moved
the lever to move the door on the heat/ac box under the hood.

Once this cable was replaced, the dash blew out hot air.

I have one of those valves under the hood to shut down the hot water to the heater but it turns out with the dash control to from heat to cool, the
door closes and there is no hot air infiltration. I never use it.

If it is your cable in trouble, look at how it is attached to the dash heater control, it can be put in back wards and will not work as it will slip
and be in operable. It sort of snaps in but if itis broken, itis hard to see this.

--
GatsbysCruise. \
74GMC260 Former Glacier Model style. \
Waukegan, Illinois \ Keep those MiniDiscs Spinning \ MY GREYHOUND IS FASTER THAN YOUR HONOR ROLL STUDENT \ WindowsXP-Win7-Win8.1-UBUNTU STUDIO -
UBUNTU VOYAGER - Berzin Auto Center
 
78. AC works well since I put a new Sanden compressor in from Applied GMC. Heat also works well. I did block off the outside air intake. Thus I only heat/cool inside air. But. I'm having some issues with the vacuum controlled air doors. At a 7 on the happy scale. Bob Dunahugh 78 Royale
 
Mine works, at least to the extent that the air-handling system...handles
air. I replaced the vacuum valve, but in my view they are unreliable. I
bought an electric valve that was mentioned here about a year ago, but have
not yet installed it.

Rick “usually not in the coach when needing heat while driving” Denney

> Let's take a poll: how many of you have coaches with the original dash
> heat in working order? Bought mine without it and haven't missed it but
> seeing
> if it's even worth getting it working again. Super involved or easy?
> --
> 1978 Kingsley -
> Kansas City, MO
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
--
Rick Denney
73 x-Glacier 230 "Jaws"
Off-list email to rick at rickdenney dot com
 
I've only owned 78 GMC. And plead ignorance on the 73-76 AC/heat systems. From what I understand. The earlier units only heated/cooled outside air. And using a hole saw on the rear of the heater box. From inside the coach. Allows inside air to get to the heater/A/C box. I've made a block off plate that doesn't allow outside air in the box. On nice temp days. To get fresh outside air in. Use the wind wings. And turn on the rear MAXXfan to 100% I've been told that it's not much effort to improve the 73 to 76 units. Bob Dunahugh 78 Royale
 
My 77 works great in all modes. Earlier, heat was not great but I have attributed that to air up high in the heater core which has resolved itself.
As Matt said water valve on GM is "vacuum to close". This default assures heat, same as loss of vacuum to selector defaults to DEF for safety reasons
I use heat position if feet cold but otherwise use VENT to throw warm air further back into the coach. Mine is stock with 100% outside air except on
max AC. If you have water flow and a correct 195 stat and your heat temp door works you should have enough heat to satisfy down to zero deg F in
cockpit.
--
John Lebetski
Woodstock, IL
77 Eleganza II
 
The dash heat/AC works in my '75. At one point, I broke the plastic pivot pin in the dash heater control, but replaced it with the machined aluminum
pin from Alex Sirum (actually purchased from Applied). In the process of replacing that pin, I cleaned and lubricated the control and it has worked
properly ever since.

A few years ago, we were heading south from Las Vegas in January on a particularly cold and wet day, and the heat would not work at all, no matter
what I did. I have since back-flushed the heater core with a garden hose, and the last time I needed the heat it was working again.

A word of caution about manual ball valves in the heater hose, if left closed all the time, the stagnant coolant will eventually rot out your heater
core. I'm guessing that is why the original heat control valve was closed under vacuum, so that it didn't sit in a closed position while not in use.

There are many vacuum lines in that system and any one of them can have small leaks which will prevent proper operation of the system. Check them
all.
--
Carl Stouffer
'75 ex Palm Beach
Tucson, AZ.
Chuck Aulgur Reaction Arm Disc Brakes, Quadrabags, 3.70 LSD final drive, Lenzi knuckles/hubs, Dodge Truck 16" X 8" front wheels, Rear American Eagles,
Solar battery charging. GMCSJ and GMCMI member
 
When we purchased our 77 Eleganza II in 1998 we went thru and completely=
refurbished the HVAC system (type 2). The type 2 system was the upgraded =
and redesigned system to fix all the past evils of the past HVAC systems us=
ed in the GMC. We replaced the following items, compressor, AC hoses, all =
heater hoses and misc parts of the AC side of the system and charged the sy=
stem with R12 which was still available. The radiator was recored with he H=
D core and the evaporator and condenser were flushed before reassembly vacu=
um checked before being charged. The HVAC would frost my knees and legs wi=
th its output and would cool the entire coach even on a HOT day. The syste=
m was rated at 3 tons cool capacity which was the same as the capacity of m=
y home that I had in Louisiana. That system worked great until we sold the=
coach in 2011. Will be rebuilding the stretch HVAC also a type 2 system, t=
his coming spring to try an achieve the same level of performance. We will=
be using Duracool as the refrigerant. JR Wright Michigan On locat=
ion in Tucson > On Dec 4, 2018, at 8:15 AM, Carl Stouffer wrote: > > The dash heat/AC works in my '75. At one point, I br=
oke the plastic pivot pin in the dash heater control, but replaced it with =
the machined aluminum > pin from Alex Sirum (actually purchased from Appl=
ied). In the process of replacing that pin, I cleaned and lubricated the c=
ontrol and it has worked > properly ever since. > > A few years ag=
o, we were heading south from Las Vegas in January on a particularly cold a=
nd wet day, and the heat would not work at all, no matter > what I did. =
I have since back-flushed the heater core with a garden hose, and the last=
time I needed the heat it was working again. > > A word of caution ab=
out manual ball valves in the heater hose, if left closed all the time, the=
stagnant coolant will eventually rot out your heater > core. I'm guessi=
ng that is why the original heat control valve was closed under vacuum, so =
that it didn't sit in a closed position while not in use. > > There ar=
e many vacuum lines in that system and any one of them can have small leaks=
which will prevent proper operation of the system. Check them > all. =
> -- > Carl Stouffer > '75 ex Palm Beach > Tucson, AZ. > Chuck =
Aulgur Reaction Arm Disc Brakes, Quadrabags, 3.70 LSD final drive, Lenzi kn=
uckles/hubs, Dodge Truck 16" X 8" front wheels, Rear American Eagles, > S=
olar battery charging. GMCSJ and GMCMI member > > ___________________=
____________________________ > GMCnet mailing list > Unsubscribe or Cha=
nge List Options: > http://list.gmcnet.org/mailman/listinfo/gmclist_list.=
gmcnet.org
 
For the dash and house water heater, the flow is restricted. Anyone know what size hole is in the in-line plug going to the dash heater and the house
water heater?
TIA
--
Larry
78 Royale w/500 Caddy
Menomonie, WI.
 
Larry,
There was a picture on the photosite somewhere, but I have not been able to find it. Vaguely remember it being a 5/16” hole. Didn’t bring my tech books this year.

JR Wright
GMC GreatLaker
GMCMI
GMC Eastern States
Michigan
On Location inTucson

>
> For the dash and house water heater, the flow is restricted. Anyone know what size hole is in the in-line plug going to the dash heater and the house
> water heater?
> TIA
> --
> Larry
> 78 Royale w/500 Caddy
> Menomonie, WI.
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
 
There is a 15/64" restrictor hole in the fitting going back into the top right rear of the intake manifold. This is where the 5/8" hoses from the heater core and the hot water heater loop lead.

Emery Stora
77 Kingsley
Frederick, CO

>
> For the dash and house water heater, the flow is restricted. Anyone know what size hole is in the in-line plug going to the dash heater and the house
> water heater?
> TIA
> --
> Larry
> 78 Royale w/500 Caddy
> Menomonie, WI.
>
 
The restriction was put there to keep the heater coil from making noise as
fluid flows.

On Tue, Dec 4, 2018 at 11:41 AM Emery Stora via Gmclist <

> There is a 15/64" restrictor hole in the fitting going back into the top
> right rear of the intake manifold. This is where the 5/8" hoses from the
> heater core and the hot water heater loop lead.
>
> Emery Stora
> 77 Kingsley
> Frederick, CO
>

> >
> > For the dash and house water heater, the flow is restricted. Anyone know
> what size hole is in the in-line plug going to the dash heater and the house
> > water heater?
> > TIA
> > --
> > Larry
> > 78 Royale w/500 Caddy
> > Menomonie, WI.
> >
>
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>

--
Jim Kanomata
Applied/GMC, Newark,CA
jimk
http://www.appliedgmc.com
1-800-752-7502
 
Hey all, thank you very much for the replies they were super helpful. Turns out there was a bypass installed but it was junk so I replaced it with a
new one from home depot. Next I noticed the PO removed the heater temperature valve that is immediately after the HVAC box. Ordered a new one should
be able to put it on this weekend.

Next question... When I turn on the valve and try and run the heat, am I going to screw something up? I'm not at all sure the condition of the heater
core or how much decades old coolant is hanging out in there. Risky move or no?
--
1978 Kingsley -
Kansas City, MO
 
Should the core leak, just disconnect the hoses and get an reducer and
connect the two hoses.

> Hey all, thank you very much for the replies they were super helpful.
> Turns out there was a bypass installed but it was junk so I replaced it
> with a
> new one from home depot. Next I noticed the PO removed the heater
> temperature valve that is immediately after the HVAC box. Ordered a new one
> should
> be able to put it on this weekend.
>
> Next question... When I turn on the valve and try and run the heat, am I
> going to screw something up? I'm not at all sure the condition of the heater
> core or how much decades old coolant is hanging out in there. Risky move
> or no?
> --
> 1978 Kingsley -
> Kansas City, MO
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>

--
Jim Kanomata
Applied/GMC, Newark,CA
jimk
http://www.appliedgmc.com
1-800-752-7502
 
We are finding several people needing to re core the heater due to leakage.

> Should the core leak, just disconnect the hoses and get an reducer and
> connect the two hoses.
>

>
>> Hey all, thank you very much for the replies they were super helpful.
>> Turns out there was a bypass installed but it was junk so I replaced it
>> with a
>> new one from home depot. Next I noticed the PO removed the heater
>> temperature valve that is immediately after the HVAC box. Ordered a new one
>> should
>> be able to put it on this weekend.
>>
>> Next question... When I turn on the valve and try and run the heat, am I
>> going to screw something up? I'm not at all sure the condition of the heater
>> core or how much decades old coolant is hanging out in there. Risky move
>> or no?
>> --
>> 1978 Kingsley -
>> Kansas City, MO
>>
>> _______________________________________________
>> GMCnet mailing list
>> Unsubscribe or Change List Options:
>> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>>
>
>
> --
> Jim Kanomata
> Applied/GMC, Newark,CA
> jimk
> http://www.appliedgmc.com
> 1-800-752-7502
>

--
Jim Kanomata
Applied/GMC, Newark,CA
jimk
http://www.appliedgmc.com
1-800-752-7502