HVAC Doors

G

Greg C.

Active member
Oct 11, 2019
256
23
28
If I remove the radiator overflow tank and the windshield washer fluid tank, can I take the front off the HVAC box and access the flapper doors?

None of mine work, probably due to the vacuum leak at the control, and it blows out the dash vents in Heat, Vent, and AC positions.

I've read that the system defaults to defrost, but mine does not, so it makes me think the door is stuck.

If I can get the doors to work, I'm thinking about trashing the original HVAC controls and doing this:

https://sites.google.com/site/darbyselky/home/electronic-hvac-controls?authuser=0

--
Greg Crawford
KM4ZCR
Knoxville, TN

"Ruby Sue"
1977 Royale
Rear Bath
403 Engine
American Eagle Wheels
Early Version Alex Sirum Quad bags
 
Greg,

The doors undoubtedly need new seals, and the evaporator probably needs
cleaning, so removing the front as you suggest is a good idea. But, you'll
gain access only to the doors themselves -- not the actuators. Those are,
unfortunately, quite well hidden behind the dash. You CAN get to them, but
not as easily as you're hoping -- so what else is new? :-)

Ken H.

On Sun, Feb 28, 2021 at 4:58 PM Greg Crawford via Gmclist <

> If I remove the radiator overflow tank and the windshield washer fluid
> tank, can I take the front off the HVAC box and access the flapper doors?
>
> None of mine work, probably due to the vacuum leak at the control, and it
> blows out the dash vents in Heat, Vent, and AC positions.
>
> I've read that the system defaults to defrost, but mine does not, so it
> makes me think the door is stuck.
>
> If I can get the doors to work, I'm thinking about trashing the original
> HVAC controls and doing this:
>
>
> https://sites.google.com/site/darbyselky/home/electronic-hvac-controls?authuser=0
>
>
> --
> Greg Crawford
> KM4ZCR
> Knoxville, TN
>
> "Ruby Sue"
> 1977 Royale
> Rear Bath
> 403 Engine
> American Eagle Wheels
> Early Version Alex Sirum Quad bags
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
 
Greg,

Another thought: You may find this chart, a color coded version of the
original in the service manual, useful. Since I completely replaced my
HVAC system years ago, I don't remember the operation of the original.
But, from this chart, it appears to me that your belief that the default
position is DEFROST may be incorrect:
bit.ly/3aZNZq7
or
http://www.gmcmhphotos.com/photos/type-ii-dash-air-condition-modification/p19227.html
Ken H.

On Sun, Feb 28, 2021 at 5:31 PM Ken Henderson
wrote:

> Greg,
>
> The doors undoubtedly need new seals, and the evaporator probably needs
> cleaning, so removing the front as you suggest is a good idea. But, you'll
> gain access only to the doors themselves -- not the actuators. Those are,
> unfortunately, quite well hidden behind the dash. You CAN get to them, but
> not as easily as you're hoping -- so what else is new? :-)
>
> Ken H.
>
>
> On Sun, Feb 28, 2021 at 4:58 PM Greg Crawford via Gmclist <

>
>> If I remove the radiator overflow tank and the windshield washer fluid
>> tank, can I take the front off the HVAC box and access the flapper doors?
>>
>> None of mine work, probably due to the vacuum leak at the control, and it
>> blows out the dash vents in Heat, Vent, and AC positions.
>>
>> I've read that the system defaults to defrost, but mine does not, so it
>> makes me think the door is stuck.
>>
>> If I can get the doors to work, I'm thinking about trashing the original
>> HVAC controls and doing this:
>>
>>
>> https://sites.google.com/site/darbyselky/home/electronic-hvac-controls?authuser=0
>>
>>
>> --
>> Greg Crawford
>> KM4ZCR
>> Knoxville, TN
>>
>> "Ruby Sue"
>> 1977 Royale
>> Rear Bath
>> 403 Engine
>> American Eagle Wheels
>> Early Version Alex Sirum Quad bags
>>
>> _______________________________________________
>> GMCnet mailing list
>> Unsubscribe or Change List Options:
>> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>>
>
 
Greg
The only damper inside the airbox on a 77 is for the defrost. If your only getting hot air, check to see if the water control on the front of the air
box is operating. Most coaches have had the original control replaced with a valve that you have to manually shut the hot water from the radiator off.
I have a 77 Royal also and I replaced my entire system with an aftermarket system that is electrically controlled. I love it! No more vacuum B/S. If
you want to talk 757-406-3233
--
Tom McManus
1977 Royale

Chesapeake VA
 
That would be a sweet set up when it is done. That is a pretty complete write up so any mods you do would be easy to figure out I would think. Sorry
I can not answer your original question. I am curious about how all the doors and vacuum controls work. I have not gotten into that part yet.

Melbo
--
Albuquerque NM Bus Conversion 1978 MCI 1973 GMC
 
Ken:

Thank you for the response. I had taken the blower motor out and then the fiberglass housing and plastic extension that holds the blower and directs
the air into the AC evaporator. There was quite a pile of Texas acorn caps and sticks in there, along with some hair. A lot of this was stuck in the
evaporator fins. I hope to be able to spray some coil cleaner from the front into the fins and clean out whatever may be left in there.

I can see one vacuum actuator from the glove box. I can see the top one by looking up under the hood and peering into the fresh air intake. Do you
know if its possible to get to the one on the drivers side of the HVAC box without removing the dash? I'd like to connect my Mity Vac to each one and
confirm operation before working on or replacing the dash control head. I definitely want to replace the foam gasketing on the doors.

I've looked at your photos of the removal and installation of your custom system several times. I'm not averse to tearing out the whole dash and
building a new one from scratch as you have done, I just don't want to do it this year if I can avoid it.

I didn't arrive at the defrost default idea on my own, I just read it somewhere on the forum.
--
Greg Crawford
KM4ZCR
Knoxville, TN

"Ruby Sue"
1977 Royale
Rear Bath
403 Engine
American Eagle Wheels
Early Version Alex Sirum Quad bags
 
Mea culpa!!! I really blew this one: My computer was very slow recovering
the first of Tom's photos -- the Old Air flyer. Seeing the 1940's
under-dash looking "thing", I somehow ignored "A/C" in the description and
only read "Heat and Defrost". After reviewing the rest of the album, I
scratched my head (easy to so with no hair up there) and wondered "Why in
the world would anyone build a system with ONLY heat???" The obvious
answer, to my Georgia boy brain, was "Gotta be a Far-North Yankee or a
Canuck". So I forgot about Tom being from Virginia and sent my email
implying, "you won't like our temperatures" email.

Tom, please accept my apologies for momentarily making you a Canuck. :-)

It's a NICE system; I'd probably have been a lot better off doing that or
something similar. I gained a little better air flow than original, but
with the OEM evaporator, no more cooling capacity.

Ken H.

On Mon, Mar 1, 2021 at 6:19 PM Tom McManus via Gmclist <

> Ken, When I do, it will be a cool ride.
> --
> Tom McManus
> 1977 Royale
>
> Chesapeake VA
>
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
 
Is there a general consensus that the evaporator is undersized in
comparison to the rest of the system and the airflow is even worse?

On Mon, Mar 1, 2021 at 4:05 PM Ken Henderson via Gmclist <

> Mea culpa!!! I really blew this one: My computer was very slow recovering
> the first of Tom's photos -- the Old Air flyer. Seeing the 1940's
> under-dash looking "thing", I somehow ignored "A/C" in the description and
> only read "Heat and Defrost". After reviewing the rest of the album, I
> scratched my head (easy to so with no hair up there) and wondered "Why in
> the world would anyone build a system with ONLY heat???" The obvious
> answer, to my Georgia boy brain, was "Gotta be a Far-North Yankee or a
> Canuck". So I forgot about Tom being from Virginia and sent my email
> implying, "you won't like our temperatures" email.
>
> Tom, please accept my apologies for momentarily making you a Canuck. :-)
>
> It's a NICE system; I'd probably have been a lot better off doing that or
> something similar. I gained a little better air flow than original, but
> with the OEM evaporator, no more cooling capacity.
>
> Ken H.
>
>
> On Mon, Mar 1, 2021 at 6:19 PM Tom McManus via Gmclist <

>
> > Ken, When I do, it will be a cool ride.
> > --
> > Tom McManus
> > 1977 Royale
> >
> > Chesapeake VA
> >
> > _______________________________________________
> > 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
>

--

*John Phillips*
 
This thread got me to thinking about HVAC air flow again, and the effective
mods some people have done to improve it. I neither indorse nor condemn
any of those, except for one aspect: DO NOT use combustible materials in
modifications, the following extract from another email, which I sent to
someone seems appropriate; it refers to a flexible plastic duct routed from
the HVAC box to the passenger side foot heater duct.:

"When John Richardson's coach had a battery fire a couple of years ago, the
flames immediately burned through a duct in that area. The fire, rather
than burning through the hood, immediately came into the cockpit, via the
melted duct, and "flowed" overhead all the way to the rear of the coach.
They were only a few yards from a fire truck so the flame was quickly
extinguished -- but the interior of the coach was destroyed -- and they
were lucky to not be burned themselves. Without that meltable/flammable
duct, there would probably have been little or no interior damage."

Whatever you do, DO NOT use combustible materials under the hood!

Ken H.

On Mon, Mar 1, 2021 at 7:17 PM John Phillips via Gmclist <

> Is there a general consensus that the evaporator is undersized in
> comparison to the rest of the system and the airflow is even worse?
>
> On Mon, Mar 1, 2021 at 4:05 PM Ken Henderson via Gmclist <

>
> > Mea culpa!!! I really blew this one: My computer was very slow
> recovering
> > the first of Tom's photos -- the Old Air flyer. Seeing the 1940's
> > under-dash looking "thing", I somehow ignored "A/C" in the description
> and
> > only read "Heat and Defrost". After reviewing the rest of the album, I
> > scratched my head (easy to so with no hair up there) and wondered "Why in
> > the world would anyone build a system with ONLY heat???" The obvious
> > answer, to my Georgia boy brain, was "Gotta be a Far-North Yankee or a
> > Canuck". So I forgot about Tom being from Virginia and sent my email
> > implying, "you won't like our temperatures" email.
> >
> > Tom, please accept my apologies for momentarily making you a Canuck. :-)
> >
> > It's a NICE system; I'd probably have been a lot better off doing that or
> > something similar. I gained a little better air flow than original, but
> > with the OEM evaporator, no more cooling capacity.
> >
> > Ken H.
> >
> >
> > On Mon, Mar 1, 2021 at 6:19 PM Tom McManus via Gmclist <

> >
> > > Ken, When I do, it will be a cool ride.
> > > --
> > > Tom McManus
> > > 1977 Royale
> > >
> > > Chesapeake VA
> > >
> > > _______________________________________________
> > > 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
> >
>
>
> --
>
> *John Phillips*
> _______________________________________________
> GMCnet mailing list
> Unsubscribe or Change List Options:
> http://list.gmcnet.org/mailman/listinfo/gmclist_list.gmcnet.org
>
 
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